Nervous System Flashcards

Question

# reverse.prompt Memory on a cellular level Long Term Potentiation

Answer 1

* for curing mental disorders: important understanding memory on the cellular level * After synapses have been used intensively for a short time, they release more neurotransmitters than before. * This phenomenon, called long-term potentiation, may be involved in memory storage.

Answer 2

i * Though the majority of each cerebral hemisphere is composed of tracts, there are **masses of gray matter deep within the white matter.** * *integrate motor commands to ensure that the proper muscle groups are stimulated or inhibited.* * Integration ensures that movements are **coordinated and smooth.** * is believed to be caused by degeneration of specific neurons in the basal nuclei.

Answer 3

Limbic System

Answer 4

These are the primary Motor and Sensory Areas of the Cortex

Answer 5

Resting Potential * Think of all the devices, such as your cell phone and laptop, that are battery-powered. Every battery is an energy source manufactured by separating positively charged ions across a membrane from negative ions. The battery’s potential energy can be used to perform work—for example, using your phone or lighting a flashlight. A resting neuron also has potential energy, much like a fully charged battery. This energy, called the resting potential, Page 283exists because the plasma membrane is polarized: Positively charged ions are stashed outside the cell, with negatively charged ions inside. * As Figure 14.4a shows, the outside of the cell is positive because positively charged sodium ions (Na+) gather around the outside of the plasma membrane. At rest, the neuron’s plasma membrane is permeable to potassium, but not to sodium. Thus, positively charged potassium ions (K+) contribute to the positive charge by diffusing out of the cell to join the sodium ions. The inside of the cell is negative in relation to the exterior of the cell because of the presence of large, negatively charged proteins and other molecules that remain inside the cell because of their size. * Figure 14.4 Generation of an action potential. a. Resting potential occurs when a neuron is not conducting a nerve impulse. During an action potential, (b) the stimulus causes the cell to reach its threshold. c. Depolarization is followed by (d) repolarization. e. A graph depicting the generation of an action potential. * Tutorial: Neuron Action Potentials * Like a battery, the neuron’s resting potential energy can be measured in volts. Whereas a D-size flashlight battery has 1.5 volts, a nerve cell typically has 0.070 volt, or 70 millivolts (mV), of stored energy (Fig. 14.4a). By convention, the voltage measurement is always a negative number. This is because scientists compare the inside of the cell—where negatively charged proteins and other large molecules are clustered—to the outside of the cell—where positively charged sodium and potassium ions are gathered. * Just like rechargeable batteries, neurons must maintain their resting potential to be able to work. To do so, neurons actively transport sodium ions out of the cell and return potassium ions to Page 284the cytoplasm. A protein carrier in the membrane, called the sodium–potassium pump, pumps sodium ions (Na+) out of the neuron and potassium ions (K+) into the neuron (see Section 3.3). This action effectively “recharges” the cell so that, like a fresh battery, it can perform work.

Answer 6

Nervous tissue

Answer 7

14.4 The Peripheral Nervous System LEARNING OUTCOMES Upon completion of this section you should be able to Describe the series of events during a spinal reflex. Distinguish between the somatic and autonomic divisions of the peripheral nervous system. Distinguish between the sympathetic and parasympathetic divisions of the autonomic division. The peripheral nervous system (PNS), which lies outside the central nervous system, contains the nerves. Nerves are designated as cranial nerves when they arise from the brain and are termed spinal nerves when they arise from the spinal cord. In any case, all nerves carry signals to and from the CNS. So right now, your eyes are sending messages by way of a cranial nerve to the brain, allowing you to read this text. When you’re finished, your brain will direct the muscles in your fingers, by way of the spinal cord and a spinal nerve, to proceed to the next chapter. Figure 14.15 illustrates the anatomy of a nerve. The cell body and the dendrites of neurons are in either the CNS or the ganglia. Ganglia (sing., ganglion) are collections of nerve cell bodies outside the CNS. The axons of neurons project from the CNS and form the spinal cord. In other words, nerves, whether cranial or spinal, are composed of axons, the long part of neurons. Figure 14.15 The structure of a nerve. The peripheral nervous system consists of the cranial nerves and the spinal nerves. A nerve is composed of bundles of axons separated from one another by connective tissue. (photo): ©Pasieka/Science Photo Library/Science Source Humans have 12 pairs of cranial nerves attached to the brain. By convention, the pairs of cranial nerves are referred to by Roman numerals (Fig. 14.16). Some cranial nerves are sensory nerves—they contain only sensory fibers; some are motor nerves that contain only motor fibers; others are mixed nerves that contain both sensory and motor fibers. Cranial nerves are largely concerned with the head, neck, and facial regions of the body. However, the vagus nerve (X) has branches not only to the pharynx and larynx but also to most of the internal organs. It arises from the brain stem—specifically, the medulla oblongata, which communicates with the hypothalamus. These two parts of the brain control the internal organs. Figure 14.16 The cranial nerves. Overall, cranial nerves receive sensory input from, and send motor outputs to, the head region. The spinal nerves receive sensory input from, and send motor outputs to, the rest of the body. Two important exceptions are the vagus nerve, X, which communicates with internal organs, and the spinal accessory nerve, XI, which controls neck and back muscles. The spinal nerves of humans emerge from either side of the spinal cord (see Fig. 14.8). There are 31 pairs of spinal nerves. The roots of a spinal nerve physically separate the axons of sensory neurons from the axons of motor neurons, forming an arrangement resembling a letter Y. The posterior root of a spinal nerve contains sensory fibers that direct sensory receptor information inward (toward the spinal cord). The cell body of a sensory neuron is in a posterior-root ganglion (also termed a dorsal-root ganglion). The anterior (also termed ventral) root of a spinal nerve contains motor fibers that conduct impulses outward (away from the cord) to the effectors. Observe in Figure 14.8 that the anterior and posterior roots join to form a spinal nerve. All spinal nerves are called mixed nerves, because they contain both sensory and motor fibers. Each spinal nerve serves the particular region of the body in which it is located. For example, the intercostal muscles of the rib cage are innervated by thoracic nerves. The Somatic System The PNS has divisions: the somatic system and the autonomic system. The nerves in the somatic system serve the skin, skeletal muscles, and tendons (see Fig. 14.2). The somatic system sensory nerves take sensory information from external sensory receptors to the CNS. Motor commands leaving the CNS travel to skeletal muscles via somatic motor nerves. Not all somatic motor actions are voluntary. Some are automatic. Automatic responses to a stimulus in the somatic system are called reflexes. A reflex occurs quickly, without your even having to think about it. For example, a reflex may cause you to blink your eyes in response to a flash of light, without your willing it. We will study the path of a reflex, because it allows us to study in detail the path of nerve signals to and from the CNS.Page 296 The Reflex Arc Figure 14.17 illustrates the path of a reflex that involves only the spinal cord. If your hand touches a sharp pin, sensory receptors in the skin generate nerve signals that move along sensory fibers through the posterior (dorsal) root ganglia toward the spinal cord. Sensory neurons that enter the cord posteriorly pass signals on to many interneurons. Some of these interneurons synapse with motor neurons whose short dendrites and cell bodies are in the spinal cord. Nerve signals travel along these motor fibers to an effector, which brings about a response to the stimulus. In this case, the effector is a muscle, which contracts so that you withdraw your hand from the pin. Various other reactions are also possible—you will most likely look at the pin, wince, and cry out in pain. This whole series of responses occurs because some of the interneurons involved carry nerve signals to the brain. The brain makes you aware of the stimulus and directs these other reactions to it. In other words, you don’t feel pain until the brain receives the information and interprets it. Figure 14.17 A spinal reflex arc. A stimulus (e.g., a sharp pin) causes sensory receptors in the skin to generate nerve signals that travel in sensory axons to the spinal cord. Interneurons integrate data from sensory neurons and then relay signals to motor neurons, causing contraction of a skeletal muscle and movement of the hand away from the stimulus. SCIENCE IN YOUR LIFE How does aspirin work? Aspirin is made of a chemical called acetylsalicylic acid (ASA). Damaged tissue produces large amounts of a type of fatty acid called prostaglandin. Prostaglandin acts as a signal to the peripheral nervous system that tissue damage has occurred, which the brain interprets as pain. Prostaglandins are manufactured in the cell by an enzyme called COX (cyclooxygenase). ASA reduces the capabilities of this enzyme, thus lowering the amount of prostaglandin produced and the perception of pain. The Autonomic System The autonomic system is also in the PNS (see Fig. 14.2). The autonomic system regulates the activity of cardiac and smooth muscles, organs, and glands. The system is divided into the sympathetic and parasympathetic divisions (Fig. 14.18). Activation of these two systems generally causes opposite responses. Figure 14.18 The two divisions of the autonomic nervous system. Sympathetic preganglionic fibers (left) arise from the thoracic and lumbar portions of the spinal cord; parasympathetic preganglionic fibers (right) arise from the cranial and sacral portions of the spinal cord. Each system innervates the same organs but has contrary effects. Although their functions are different, the two divisions share some features: (1) They usually function in an involuntary manner; (2) they innervate all internal organs; and (3) they use two neurons and one ganglion for each impulse. The first neuron has a cell body within the CNS and a preganglionic fiber that enters the ganglion. The second neuron has a cell body within a ganglion and a postganglionic fiber that leaves the ganglion. Reflex actions, such as those that regulate blood pressure and breathing rate, are especially important to the maintenance of homeostasis. These reflexes begin when the sensory neurons in contact with internal organs send messages to the CNS. They are completed by motor neurons within the autonomic system. Sympathetic Division Most preganglionic fibers of the sympathetic division arise from the middle portion of the spinal cord. They terminate almost immediately in ganglia that lie near the cord. The sympathetic division is especially important during emergency situations when you might be required to fight or take flight. It accelerates the heartbeat and dilates the bronchi—active muscles, after all, require a ready supply of glucose and oxygen. Page 297Sympathetic neurons inhibit the digestive organs, as well as the kidneys and urinary bladder; the activities of these organs—digestion, defecation, and urination—are not immediately necessary if you’re under attack. The neurotransmitter released by the postganglionic axon is primarily norepinephrine (NE). The structure of NE is like that of epinephrine (adrenaline), an adrenal medulla hormone that usually increases heart rate and contractility. Parasympathetic Division The parasympathetic division includes a few cranial nerves (e.g., the vagus nerve), as well as fibers that arise from the sacral (bottom) portion of the spinal cord. Therefore, this division is often referred to as the craniosacral portion of the autonomic system. In the parasympathetic division, the preganglionic fiber is long, and the postganglionic fiber is short because the ganglia lie near or within the organ. The parasympathetic division, sometimes called the housekeeper division, promotes all the internal responses we associate with a relaxed state. For example, it causes the pupil of the eye to contract, promotes digestion of food, and slows heart rate. It has been suggested that the parasympathetic system could be called the rest-and-digest system. The neurotransmitter used by the parasympathetic division is acetylcholine (ACh). The Somatic Versus the Autonomic Systems Recall that the PNS includes the somatic system and the autonomic system. Table 14.1 compares the features and functions of the somatic motor pathway with the motor pathways of the autonomic system. Table 14.1Comparison of Somatic Motor and Autonomic Motor Pathways Table Summary: Columns are for somatic motor pathway and autonomic motor pathways. Rows are for different points of comparison. Autonomic motor pathways are grouped into sympathetic and parasympathetic, as the other column-headers. Autonomic Motor Pathways Somatic Motor PathwaySympatheticParasympathetic Type of controlVoluntary/involuntaryInvoluntaryInvoluntary Number of neurons per messageOneTwo (preganglionic shorter than postganglionic)Two (preganglionic longer than postganglionic) Location of motor fiberMost cranial nerves and all spinal nervesThoracolumbar spinal nervesCranial (e.g., vagus) and sacral spinal nerves NeurotransmitterAcetylcholineNorepinephrineAcetylcholine EffectorsSkeletal musclesSmooth and cardiac muscle, glands, and organsSmooth and cardiac muscle, glands, and organs CHECK YOUR PROGRESS 14.4 Contrast cranial and spinal nerves. Answer The 12 pairs of cranial nerves receive sensory input from and send motor outputs primarily to the head region. The 31 pairs of spinal nerves receive sensory input from and send motor outputs to the rest of the body. Detail the fastest way for you to react to a stimulus. Answer A reflex action is fastest when it involves just the reflex arc that passes only through the spinal cord, not the brain. Predict what could happen to homeostasis if the autonomic nervous system failed. Answer Without the autonomic nervous system, activities of the cardiac muscles, smooth muscles, and glands would have to be regulated voluntarily. Maintaining homeostasis would be an overwhelming task. CONNECTING THE CONCEPTS For more on the interaction of the PNS with the other systems of the body, refer to the following discussions: Section 5.3 explores how the divisions of the autonomic system regulate the heart rate and help maintain homeostasis. Section 10.5 examines how signals between the brain and the diaphragm control the rate of breathing. Section 15.1 provides an overview of the types of sensory inputs processed by the peripheral nervous system.

Answer 8

neurotransmitters

Answer 9

Basal Nuclei Though the majority of each cerebral hemisphere is composed of tracts, there are masses of gray matter deep within the white matter. These basal nuclei integrate motor commands to ensure that the proper muscle groups are stimulated or inhibited. Integration ensures that movements are coordinated and smooth. Parkinson disease (see Section 18.5) is believed to be caused by degeneration of specific neurons in the basal nuclei.

Answer 10

* cerebral cortex: thin, outer layer of gray matter 1. Primary motor area – voluntary control of skeletal muscle • 2. Primary somatosensory area – for sensory information from skeletal muscle and skin 3. Association areas – integration occurs here 4. Processing centers – perform higher level analytical functions including Wernicke’s and Broca’s areas, both involved in speech.

Answer 11

Synaptic Integration

Answer 12

The Spinal Cord

Answer 13

Action Potential - Polarization

Answer 14

1. The brain coordinates the _voluntary control of our limbs_. 2. Motor signals originating in the brain pass down **descending tracts** to the ***_spinal cord and out to our muscles by way of motor fibers_*** (see Fig. 14.2b, black arrows). * Therefore, if the spinal cord is severed, we suffers 1. a loss of sensation and a 2. loss of voluntary control—paralysis. 3. If the cut occurs in the thoracic region, the lower body and legs are paralyzed, a condition known as **paraplegia.** If the injury is in the neck region, all four limbs are usually affected, a condition called quadriplegia. 3.

Answer 15

14.2 The Central Nervous System LEARNING OUTCOMES Upon completion of this section, you should be able to Identify the structures of the spinal cord and provide a function for each. Identify the structures of the brain and provide a function for each. Identify the lobes and major areas of the human brain. Distinguish between the functions of the primary motor and the primary somatosensory areas of the brain.

Answer 16

The nervous system receives sensory input.

Answer 17

Physiology of a Neuron

Answer 18

The Spinal Cord Download, attach image and study it, 14.8 a Figure 14.8b Figure 14.8 (Fig. 14.8a–c). The organization of white and gray matter in the spinal cord and the spinal nerves. a. Cross-section of the spinal cord, showing arrangements of white and gray matter. b. Spinal nerves originating from the spinal cord. c. The spinal cord is protected by vertebrae. d. Spinal nerves emerging from the cord.

Answer 19

Functions of the Spinal Cord The spinal cord provides a means of communication between the brain and the peripheral nerves that leave the cord. When someone touches your hand, sensory receptors generate nerve signals that pass through sensory fibers to the spinal cord and up ascending tracts to the brain (see Fig. 14.2b, red arrows). The gate control theory of pain proposes that the tracts in the spinal cord have “gates” and that these gates control the flow of pain messages from the peripheral nerves to the brain. Depending on how the gates process a pain signal, the pain message can be allowed to pass directly to the brain or can be prevented from reaching the brain. Pain messages may also be blocked by other inputs, such as those received from touch receptors or endorphins. The brain coordinates the voluntary control of our limbs. Motor signals originating in the brain pass down descending tracts to the spinal cord and out to our muscles by way of motor fibers (see Fig. 14.2b, black arrows). Therefore, if the spinal cord is severed, we suffer a loss of sensation and a loss of voluntary control—paralysis. If the cut occurs in the thoracic region, the lower body and legs are paralyzed, a condition known as paraplegia. If the injury is in the neck region, all four limbs are usually affected, a condition called quadriplegia.

Answer 20

1. , which lies outside the central nervous system, contains the nerves. 2. Nerves are designated as cranial nerves when they arise from the brain and are termed spinal nerves when they arise from the spinal cord. In any case, all nerves carry signals to and from the CNS. So right now, your eyes are sending messages by way of a cranial nerve to the brain, allowing you to read this text. When you’re finished, your brain will direct the muscles in your fingers, by way of the spinal cord and a spinal nerve, to proceed to the next chapter. 3. Figure 14.15 illustrates the anatomy of a nerve. The cell body and the dendrites of neurons are in either the CNS or the ganglia. Ganglia (sing., ganglion) are collections of nerve cell bodies outside the CNS. The axons of neurons project from the CNS and form the spinal cord. In other words, nerves, whether cranial or spinal, are composed of axons, the long part of neurons.

Answer 21

Basal Nuclei What is integration? What is Parkinson's disease?

Answer 22

Structure of the Spinal Cord A cross-section of the spinal cord (Fig. 14.8a) shows a central canal, gray matter, and white matter. Figure 14.8b shows how an individual vertebra protects the spinal cord. The spinal nerves project from the cord through small openings called intervertebral foramina. Fibrocartilage intervertebral discs separate the vertebrae. If a disc ruptures or herniates, it may compress a spinal nerve, resulting in pain and a loss of mobility. Figure 14.8 The organization of white and gray matter in the spinal cord and the spinal nerves. a. Cross-section of the spinal cord, showing arrangements of white and gray matter. b. Spinal nerves originating from the spinal cord. c. The spinal cord is protected by vertebrae. d. Spinal nerves emerging from the cord. (a): ©Scientifica/Corbis Documentary/Getty Images; (d): ©McGraw-Hill Education/Rebecca Gray, photographer & Don Kincaid, dissections The central canal of the spinal cord contains cerebrospinal fluid, as do the meninges that protect the spinal cord. The gray matter is centrally located and shaped like the letter H (Fig. 14.8a–c). Portions of sensory neurons and motor neurons are found in gray matter, as are interneurons that communicate with these two types of neurons. The dorsal root of a spinal nerve contains sensory fibers entering the gray matter. The ventral root of a spinal nerve contains motor fibers exiting the gray matter. The dorsal and ventral roots join before the spinal nerve leaves the vertebral canal (Fig. 14.8c, d), forming a mixed nerve. Spinal nerves are a part of the PNS. The white matter of the spinal cord occurs in areas around the gray matter. The white matter contains ascending tracts taking information to the brain (primarily located posteriorly) and descending tracts taking information from the brain (primarily located anteriorly). Many tracts cross just after they enter and exit the brain, so the left side of the brain controls the right side of the body. Likewise, the right side of the brain controls the left side of the body.

Answer 23

SCIENCE IN YOUR LIFE How does aspirin work? Aspirin is made of a chemical called acetylsalicylic acid (ASA). Damaged tissue produces large amounts of a type of fatty acid called prostaglandin. Prostaglandin acts as a signal to the peripheral nervous system that tissue damage has occurred, which the brain interprets as pain. Prostaglandins are manufactured in the cell by an enzyme called COX (cyclooxygenase). ASA reduces the capabilities of this enzyme, thus lowering the amount of prostaglandin produced and the perception of pain.

Answer 24

* 14.2 The Central Nervous System 23 3. The brain: Cerebellum • Receives and integrates sensory input from the eyes, ears, joints, and muscles about the current position of the body • Functions • Maintains posture • Coordinates voluntary movement • Allows learning of new motor skills (i.e., playing the piano or hitting a baseball) 1

Answer 25

A lipid covering on long axons that acts to increase the speed of nerve impulse conduction, insulation for both CNS and PNS, and regeneration in the PNS • Schwann cells – neuroglia that make up the myelin sheath in the PNS • Oligodendrocytes- neuroglia that make up the myelin sheath in the CNS • Nodes of Ranvier – gaps between myelination on the axons • Saltatory conduction – conduction of the nerve impulse from node to node

Answer 26

Table 14.2Drug Influence on the CNS Table Summary: Table lists the names of different substances in column 1. Other information related to these substances appears in columns 2 and 3. SubstanceEffectMode of Transmission AlcoholDepressantDrink NicotineStimulantSmoked or smokeless tobacco CocaineStimulantSniffed/snorted, injected, or smoked Methamphetamine/EcstasyStimulantSmoked or pill form HeroinDepressantSniffed/snorted, injected, or smoked Marijuana/K2PsychoactiveSmoked or consumed Beginning in about 2005, several manufacturers began selling alcoholic energy drinks. With names like Four Loko, JOOSE, and Sparks, these drinks combine fairly high levels of alcohol with caffeine and other ingredients. Although interactions between drugs can be complex, the stimulant effects of caffeine can counteract some of the depressant effects of alcohol, so users feel able to drink more. Because caffeine does not reduce the intoxicating effects of alcohol, many state legislatures are banning these products, and in November 2010 the U.S. Food and Drug Administration warned several manufacturers that they would no longer be allowed to mix caffeine with alcohol in their products. Nicotine Although the numbers have been decreasing since 2011 according to the CDC, in 2015, 25.3% of high school students and 7.4% of middle school students reported using a tobacco product. When tobacco is smoked or chewed, nicotine is rapidly delivered throughout the body. It causes a release of epinephrine from the adrenal glands, increasing blood sugar and causing the initial feeling of stimulation. As blood sugar falls, depression and fatigue set in, causing the user to seek more nicotine. In the CNS, nicotine stimulates neurons to release dopamine, a neurotransmitter that promotes a temporary sense of pleasure, and reinforces dependence on the drug. About 70% of people who try smoking become addicted. As mentioned in earlier chapters, smoking is strongly associated with serious diseases of the cardiovascular and respiratory systems. Once addicted, however, only 10–20% of smokers are able to quit. Most medical approaches to quitting smoking involve the administration of nicotine in safer forms, such as skin patches, gum, or a newly developed nicotine inhaler, so that withdrawal symptoms can be minimized while dependence is gradually reduced. Several antinicotine vaccines (such as NicVAX) are currently in development or in early clinical trials. These vaccines stimulate the production of antibodies that prevent nicotine from entering the brain. Cocaine and Crack Cocaine is an alkaloid derived from the shrub Erythroxylon coca. Approximately 35 million Americans have used cocaine by sniffing/snorting, injecting, or smoking. Cocaine is a powerful stimulant in the CNS that interferes with the reuptake of dopamine at synapses, increasing overall brain activity. The result is a rush of a sense of well-being that lasts from 5 to 30 minutes. However, long-term use of cocaine causes a loss of metabolic functions in the brain (Fig. 14.19). Figure 14.19 Cocaine use. Brain activity before and after the use of cocaine. (both photos): ©Science Source “Crack” is the street name given to cocaine that is processed to a free-base form for smoking. The term crack refers to the crackling sound heard when the drug is smoked. Smoking allows high doses of the drug to reach the brain rapidly, providing an intense and immediate high, or “rush.” Approximately 8 million Americans use crack. A cocaine binge is a period in which a user takes the drug at ever-higher doses. The user is hyperactive, with little desire for food or sleep, but has an increased sex drive. This is followed by a crash period, characterized by fatigue, depression, irritability, and a lack of interest in sex. In fact, men who use cocaine often become impotent. Cocaine is highly addictive; with continued use, the brain makes less dopamine to compensate for a seemingly endless supply. The user experiences withdrawal symptoms and an intense craving for cocaine. Overdosing on cocaine can cause cardiac and/or respiratory arrest.Page 301 Methamphetamine and Ecstasy Methamphetamine and ecstasy are considered club, or party, drugs. Methamphetamine (commonly called meth or crank) is a powerful CNS stimulant. Meth is often produced in makeshift home laboratories, usually starting with ephedrine or pseudoephedrine, common ingredients in many cold and asthma medicines. As a result, many states have passed laws making these medications more difficult to purchase. The number of toxic chemicals used to prepare the drug makes a former meth lab site hazardous to humans and to the environment. Over 9 million people in the United States have used methamphetamine at least once. It is available as a powder that can be snorted or as crystals (crystal meth or ice) that can be smoked. The structure of methamphetamine is similar to that of dopamine, and the most immediate effect of taking meth is a rush of euphoria, energy, alertness, and elevated mood. However, this is typically followed by a state of agitation that, in some individuals, leads to violent behavior. Chronic use can result in what is called an amphetamine psychosis, characterized by paranoia, hallucinations, irritability, and aggressive, erratic behavior. Ecstasy is the street name for MDMA (methylenedioxymethamphetamine), which is chemically similar to methamphetamine. Many users say that “X,” taken as a pill that looks like an aspirin or candy, increases their feelings of well-being and love for other people. However, it has many of the same side effects as other stimulants, plus it can interfere with temperature regulation, leading to hyperthermia, high blood pressure, and seizures. Although deaths from alcohol abuse are more common, ecstasy is identified as a cause of accidental death in young adults each year. Drugs with sedative effects, known as date rape or predatory drugs, include flunitrazepam (Rohypnol, or roofies), gamma-hydroxybutyric acid (GHB), and ketamine (special K). Ketamine is actually a drug that veterinarians sometimes use to perform surgery on animals. Any of these drugs can be given to an unsuspecting person, who may fall into a dreamlike state in which he or she is unable to move and thus is vulnerable to sexual assault. Heroin Heroin is derived from the resin or sap of the opium poppy plant, which is widely grown in a region from Turkey to Southeast Asia and in parts of Latin America. Drugs derived from opium are called opiates, or more commonly, opioids. This class also includes morphine and codeine. After heroin is injected, snorted, or smoked, a feeling of euphoria, along with relief of any pain, occurs within a few minutes. It is estimated that 4 million Americans have used heroin sometime in their lives, and over 300,000 people use heroin annually. As with other drugs of abuse, addiction is common. Heroin and opioids bind to receptors meant for the endorphins, naturally occurring neurotransmitters that kill pain and produce feelings of tranquility. With repeated use, the body’s production of endorphins decreases. Tolerance develops, so the user needs to take more of the drug just to prevent withdrawal symptoms (tremors, restlessness, cramps, vomiting), and the original euphoria is no longer felt. In the case of heroin, long-term users commonly acquire hepatitis, HIV/AIDS, and various bacterial infections due to the use of shared needles, and heavy users may experience convulsions and death by respiratory arrest. Heroin addiction can be treated with synthetic opiate compounds, such as methadone or buprenorphine and naloxone (Suboxone), that decrease withdrawal symptoms and block heroin’s effects. However, methadone itself can be addictive, and methadone-related deaths are on the rise. Marijuana and K2 Marijuana is the most commonly used illegal drug in the United States. Surveys vary, but in 2015, about 52% of young adults reported using marijuana in their lifetime, and 46% of the U.S. population had tried it at least once. It is derived from the dried flowering tops, leaves, and stems of the marijuana plant, Cannabis sativa, which contain and are covered by a resin that is rich in THC (tetrahydrocannabinol). The names cannabis and marijuana apply to either the plant or THC. Marijuana can be ingested, but usually it is smoked in a cigarette called a “joint.” Beginning with California in 1996, several states have legalized its use for medical purposes, such as in treating cancer, AIDS, and glaucoma. In 2012, Colorado became the first state to legalize recreational use. As of 2018, 8 states had joined Colorado in legalizing recreational use, and 22 additional states had authorized the use of marijuana for medicinal purposes. However, in 2005, the Supreme Court ruled that patients prescribed medical marijuana can still be prosecuted by federal agencies. Page 302Researchers have found that THC binds to a receptor for anandamide, a naturally occurring neurotransmitter that is important for short-term memory processing, and perhaps for feelings of contentment. The occasional marijuana user experiences mild euphoria, along with alterations in vision and judgment. Heavy use can cause hallucinations, anxiety, depression, paranoia, and psychotic symptoms. Research is underway to identify the effects of long-term marijuana use on the brain, as well as on the effects of secondhand marijuana smoke on the respiratory system. In recent years, awareness has been increasing about a synthetic compound called K2, or spice. Originally synthesized by an organic chemist at Clemson University, K2 is about ten times as potent as THC. The chemical is typically sprayed onto a mixture of other herbal products and smoked. However, because there is no regulation of how it is produced, the amount of K2 itself, or contaminants, can vary greatly. This may account for the several reports of serious medical problems and even deaths among K2 users. CHECK YOUR PROGRESS 14.5 Contrast drug therapy and drug abuse. Answer Drug therapy is used to treat a disease or disorder. Drug abuse is using drugs without symptoms of disease or disorder. List how the abuse of drugs, including alcohol and nicotine, affects the nervous system. Answer Alcohol and heroin are depressants; nicotine, cocaine, and methamphetamines are stimulants; marijuana produces euphoria. Detail several modes of action of pharmaceutical and illegal drugs. Answer Alcohol increases the action of GABA and increases the release of endorphins in the hypothalamus. Nicotine stimulates dopamine release. Cocaine inhibits dopamine reuptake. Methamphetamine mimics the action of cocaine. Heroin is converted to morphine in the brain and binds to opioid receptors. Marijuana stimulates anandamide receptors. CONNECTING THE CONCEPTS For more on the long-term effects of drug use on the systems of the body, refer to the following discussions: Section 5.7 explores the negative long-term effects of smoking on the cardiovascular system. Section 11.4 provides information on how alcohol acts as a diuretic in the urinary system. Section 20.2 examines the relationship between smoking and alcohol use and the increased risk of cancer. CONCLUSION The cause of multiple sclerosis (MS) is still unknown, but most researchers agree that there are most likely many contributing factors, including environmental influences, genetics, and a faulty immune system. Many individuals with MS are able to control their symptoms by using immunosuppressive medications, such as beta interferons. The fact that this treatment works suggests that, in many cases, MS is caused by the immune system incorrectly identifying the myelin sheaths as foreign material. The breakdown of the myelin can be detected using both MRI and SSEP tests (discussed in the chapter opener). However, environmental conditions are also suspected to cause MS. Studies have shown that the risk of contracting MS is influenced in part by where in the world you live, although the specific environmental factor or pollutant has not yet been identified. Genetics is also believed to play a role in some cases. But most researchers believe that a defect in a single gene is unlikely. Rather, it is more likely that a certain combination of genetic factors places an individual at a higher risk of contracting MS. Though there is no cure for MS, researchers have been very successful in developing disease-modifying drugs that reduce the symptoms and allow the individual to lead a normal life.

Answer 27

This is the human brain

Answer 28

Central White Matter

Answer 29

The cerebellum lies under the occipital lobe of the cerebrum and is separated from the brain stem by the fourth ventricle. The cerebellum has two portions joined by a narrow median portion. Each portion is primarily composed of white matter. In a longitudinal section, the white matter has a treelike pattern called arbor vitae. Overlying the white matter is a thin layer of gray matter that forms a series of complex folds. The cerebellum receives sensory input from the eyes, ears, joints, and muscles about the present position of body parts. It also receives motor output from the cerebral cortex about where these parts should be located. After integrating this information, the cerebellum sends motor signals by way of the brain stem to the skeletal muscles. In this way, the cerebellum maintains posture and balance. It also ensures that all the muscles work together to produce smooth, coordinated, voluntary movements. The cerebellum assists in the learning of new motor skills, such as playing the piano or hitting a baseball.

Answer 30

• 2 divisions – Central nervous system (CNS): –Brain and spinal cord –Peripheral nervous system (PNS): Nerves and ganglia (collections of cell bodies)

Answer 31

1. Language: * semantic memory; * Seeing and hearing words depends on sensory centers in the **occipital and temporal lobes**, respectively. 1. Damage to Wernicke’s area: the inability to comprehend speech. 2. Damage to Broca’s area: the inability to speak and write. 3. * 4. re: language & speech: left brain and the right brain may have different functions. * Recall that the **left hemisphere** contains **_both Broca’s area and Wernicke’s area_** (see Section 14.2). * As you might expect, it appears that the left hemisphere plays a role of great importance in language functions. * The role of the isolated left hemisphere can be studied in patients after surgery to sever the **corpus callosum.** This procedure is used for seizure control in patients with **epilepsy.** After surgery, the patient is termed “split brain,” because there is no longer direct communication between the two cerebral hemispheres. If a **_split-brain individual v_**iews an object with only the right eye, its image will be sent only to the right hemisphere. This person will be able to choose the proper object for a particular use—scissors to cut paper, for example—but will be unable to name that object. * * Researchers now believe that the hemispheres process the same information differently. **The left hemisphere is more global, whereas the right hemisphere is more specific in its approach**. However, research also indicates that the classification of “right-brained” versus “left-brained” for individuals is probably not an accurate indication of an individual’s brain activity

Answer 32

lies entirely within the CNS. Interneurons can receive input from sensory neurons and from other interneurons in the CNS. Thereafter, they sum up all the information received from other neurons before they communicate with motor neurons.

Answer 33

* naturally occurring molecules that block the release of a neurotransmitter or modify a neuron’s response to a neurotransmitter. * _Two well-known neuromodulators are :_ 1. **Substance P**: neuropeptide that is released by sensory neurons when pain is present. 2. **Endorphins.** *

Answer 34

Brain **_Brain Stem_** 14.2 Lecture notes

Answer 35

See, download, review and study the following diagrams: **Figure 14.3** **The structure of sensory neurons, interneurons, and motor neurons.**

Answer 36

Action potential animation

Answer 37

Time to download all photographs, review slides, do PLQ again and review adaptive learning along with flash cards and making study guide for Chapter Nervous System!

Answer 38

(Fig. 14.8c, d)

Answer 39

Propagation of an Action Potential If an axon is unmyelinated, an action potential at one locale stimulates an adjacent part of the axon membrane to produce an action potential. Conduction along the entire axon in this fashion can be rather slow—approximately 1 meter/second (1 m/s) in thin axons—because each section of the axon must be stimulated. Action Potential Propagation In myelinated fibers, an action potential at one node of Ranvier causes an action potential at the next node, jumping over the entire myelin-coated portion of the axon. This type of conduction is called saltatory conduction (saltatio is a Latin word that means “to jump”) and is much faster. In thick, myelinated fibers, the rate of transmission is more than 100 m/s. Regardless of whether an axon is myelinated or not, its action potentials are self-propagating. Each action potential generates another, along the entire length of the axon. Like the action potential itself, conduction of an action potential is an all-or-none event—either an axon conducts its action potential or it does not. The intensity of a message is determined by how many action potentials are generated within a given time. An axon can conduct a volley of action potentials very quickly, because only a small number of ions are exchanged with each action potential. Once the action potential is complete, the ions are rapidly restored to their proper place through the action of the sodium–potassium pump. Neural Transmission: Action Potential Propagation As soon as the action potential has passed by each successive portion of an axon, that portion undergoes a short refractory period, during which it is unable to conduct an action potential. This ensures the one-way direction of a signal from the cell body down the length of the axon to the axon terminal. It is interesting to note that all functions of the nervous system, from our deepest emotions to our highest reasoning abilities, are dependent on the conduction of nerve signals.

Answer 40

A group of brain structures that blends primitive emotions and higher mental functions into a united whole.

Answer 41

CNS Autonomic Nervous System Sympathic Nervous System and Parasympathetic Nervous System

Answer 42

14.4 The Peripheral Nervous System LEARNING OUTCOMES Upon completion of this section you should be able to Describe the series of events during a spinal reflex. Distinguish between the somatic and autonomic divisions of the peripheral nervous system. Distinguish between the sympathetic and parasympathetic divisions of the autonomic division.

Answer 43

**_This is action potential of a neuron._** **_Another word for action potential is:_** List the steps in the process of action potential: See, Download and Study Figure 14.4b

Answer 44

1. Cerebrum • * * The cerebrum is the largest portion of the brain • * Divided into 4 lobes: * 1. **Frontal lobe**: primary motor area and conscious thought * **2. Temporal lobe**: primary auditory, smell, and speech area * 3**. Parietal lobe:** primary somatosensory and taste area * 4. **Occipital lobe:** primary visual area * * 14.2 The Central Nervous System 16 1. * 2. Cerebral hemispheres • 3. Cerebral cortex • 4. Primary motor and sensory areas of the cortex • 5. Association areas • 6. Processing centers • 7. Central white matter 8.

Answer 45

* 1. receive information from the other association areas 2. and perform **higher-level analytical functions**. * The **_prefrontal area,_** * **__** frontal lobe, receives information from the other association areas and uses to **_reason and plan our actions._** * **_Integration_** in this area accounts for our most cherished human abilities. *Reasoning, critical thinking, and formulating appropriate behaviors* are possible because of integration carried out in the prefrontal area. * The unique ability of humans to **speak** is partially dependent on **_two processing centers_** found only in the **_left cerebral cortex_**. 1. **_Wernicke’s area_** is located in the posterior part of the left **temporal lobe:** helps us **understand** both the written and the spoken word and sends the information to Broca’s area. 2. **_Broca’s area_** is located in the **left frontal lobe.** * anterior to the portion of the primary motor area for speech **musculatur**e (lips, tongue, larynx, and so forth) * adds grammatical refinements * and directs the primary motor area to stimulate the appropriate muscles for speaking and writing. 1.

Answer 46

Peripheral Nervous System (PNS) * Figure 14.15 illustrates the anatomy of a nerve. The cell body and the dendrites of neurons are in either the CNS or the ganglia. Ganglia (sing., ganglion) are collections of nerve cell bodies outside the CNS. The axons of neurons project from the CNS and form the spinal cord. In other words, nerves, whether cranial or spinal, are composed of axons, the long part of neurons. Figure 14.15 The structure of a nerve. The peripheral nervous system consists of the cranial nerves and the spinal nerves. A nerve is composed of bundles of axons separated from one another by connective tissue. \*\* Download, review and look

Answer 47

Limbic System (14.2) Function Structurally (Fig. 14.13) Page 293 The regions of the brain associated with the limbic system. In the limbic system (purple), structures deep within each cerebral hemisphere and surrounding the diencephalon join higher mental functions, such as reasoning, with more primitive feelings, such as fear and pleasure. Therefore, primitive feelings can influence our behavior, but reason can also keep them in check.

Answer 48

Functions of the Spinal Cord (see Fig. 14.2b, red arrows).

Answer 49

1. contains motor areas and sensory areas 2. association areas * The primary motor area is in the 1. frontal lobe just anterior to (before) the central sulcus 1. **Voluntary commands** to skeletal muscles begin in the primary motor area, and each part of the body is controlled by a certain section 2. (Fig. 14.11a). In this illustration, notice that large areas of the cerebral cortex are devoted to **controlling structures** that carry out very **fine, precise movements.** 1. ****Thus, the muscles that control facial movements—swallowing, salivation, expression—take up an especially large portion of the primary motor area. Likewise, hand movements require tremendous accuracy. Together, these two structures command nearly two-thirds of the primary motor area. **Figure 14.11** The primary motor and primary somatosensory areas of the brain. a. The primary motor area (blue) is located in the frontal lobe, adjacent to (b) the primary somatosensory area in the parietal lobe. The primary taste area is colored pink. The size of each body region shown indicates the relative amount of cortex devoted to control of that body region.

Answer 50

* axon branches into many fine endings, each tipped by a small swelling called an **_axon terminal._** * Each terminal lies very close to either the dendrite or the cell body of another neuron, area called **_synapse_** (Fig. 14.5). At a synapse, a small gap called the **_synaptic cleft_** 1. separates the sending neuron from the receiving neuron. The nerve signal is unable to jump the cleft. Therefore: 2. The nerve signal is unable to jump the cleft. Therefore, another means is needed to pass the nerve signal from the sending neuron to the receiving neuron.

Answer 51

The peripheral nervous system (PNS) consists of nerves. Nerves lie outside the CNS. The division between the CNS and the PNS is arbitrary. The two systems work together and are connected to each other (Fig. 14.2).

Answer 52

Cerebrum—largest part of the brain, integrates sensory inputs and coordinates the activities of the other parts of the brain; diencephalon—contains the hypothalamus and thalamus, maintains homeostasis, receives sensory input; cerebellum—sends out motor impulses by way of the brain stem to the skeletal muscles, produces smooth, coordinated voluntary movements; brain stem—contains the midbrain, pons, and medulla oblongata, acts as a relay station, and the medulla has reflex centers.

Answer 53

Spinal Cord

Answer 54

Neurotransmitter Molecules More than 100 substances are known or suspected to be neurotransmitters. Some of the more common ones in humans are acetylcholine, norepinephrine, dopamine, serotonin, glutamate, and GABA (gamma aminobutyric acid). Neurotransmitters transmit signals between nerves. Nerve-muscle, nerve-organ, and nerve-gland synapses also communicate using neurotransmitters. Acetylcholine (ACh) and norepinephrine are active in both the CNS and PNS. In the PNS, these neurotransmitters act at synapses called neuromuscular junctions. We will explore the structure of the neuromuscular junctions in Section 13.2. In the PNS, ACh excites skeletal muscle but inhibits cardiac muscle. It has either an excitatory or inhibitory effect on smooth muscle or glands, depending on their location. Norepinephrine generally excites smooth muscle. In the CNS, norepinephrine is important to dreaming, waking, and mood. Serotonin is involved in thermoregulation, sleeping, emotions, and perception. Many drugs that affect the nervous system act at the synapse. Some interfere with the actions of neurotransmitters, and other drugs prolong the effects of neurotransmitters (see Section 14.5).

Answer 55

1. In interneurons and motor neurons * multiple dendrites take signals to the cell body, and then an * axon conducts nerve signals away from the cell body. 2. In sensory neurons, * a very long axon carries nerve signals from the dendrites associated with a sensory receptor to the CNS, and this * axon is interrupted by the cell body.

Answer 56

1. integrates our emotions (fear, joy, sadness) 2. with our higher mental functions (reason, memory). 3. Because of the limbic system, activities such as sexual behavior and eating seem pleasurable, and mental stress can cause high blood pressure.

Answer 57

This neuron takes nerve impulses away from the CNS to an effector (muscle fiber, organ, or gland). Effectors carry out our responses to environmental changes, whether these are external or internal.

Answer 58

1. generates an action potential * that moves along the length of an axon. 1. An action potential in one location * stimulates the production of an action potential in an adjacent part of the axon membrane. * If the nerve is myelinated, the action potential moves more quickly, “jumping” from one node of Ranvier to the next.

Answer 59

This part of the brain is the largest and this is what it's function is

Answer 60

The Spinal Cord has these functions: These can result from severed spinal cords

Answer 61

14.3 The Limbic System and Higher Mental Functions LEARNING OUTCOMES Upon completion of this section, you should be able to Identify the structures of the limbic system. Explain how the limbic system is involved in memory, language, and speech. Summarize the types of memory associated with the limbic system. The limbic system integrates our emotions (fear, joy, sadness) with our higher mental functions (reason, memory). Because of the limbic system, activities such as sexual behavior and eating seem pleasurable, and mental stress can cause high blood pressure. Limbic System The limbic system is an evolutionary ancient group of linked structures deep within the cerebrum. It is a functional grouping rather than an anatomical one (Fig. 14.13). The limbic system blends primitive emotions and higher mental functions into a united whole. As already noted, it accounts for why activities such as sexual behavior and eating seem pleasurable. Conversely, unpleasant sensations or emotions (pain, frustration, hatred, despair) are translated by the limbic system into a stress response. Figure 14.13 The regions of the brain associated with the limbic system. In the limbic system (purple), structures deep within each cerebral hemisphere and surrounding the diencephalon join higher mental functions, such as reasoning, with more primitive feelings, such as fear and pleasure. Therefore, primitive feelings can influence our behavior, but reason can also keep them in check. Two significant structures in the limbic system are the amygdala and the hippocampus. The amygdala, in particular, can cause experiences to have emotional overtones, and it creates the sensation Page 293of fear. This center can use past knowledge fed to it by association areas to assess a current situation. If necessary, the amygdala can trigger the fight-or-flight reaction. So if you are out late at night and you turn to see someone in a ski mask following you, the amygdala may immediately cause you to start running. The frontal cortex can override the limbic system, cause you to rethink the situation, and prevent you from acting out strong reactions. The hippocampus is believed to play a crucial role in learning and memory. The hippocampal region acts as an information gateway during the learning process. It determines what information about the world is to be sent to memory and how this information is to be encoded and stored by other regions in the brain. Most likely, the hippocampus can communicate with the frontal cortex, because we know that memories are an important part of our decision-making processes. Higher Mental Functions As in other areas of biological research, brain research has progressed due to technological breakthroughs. Neuroscientists now have a wide range of techniques at their disposal for studying the human brain, including modern technologies that allow us to record its functioning. Memory and Learning Just as the connecting tracts of the corpus callosum are evidence that the two cerebral hemispheres work together, so the limbic system indicates that cortical areas may work with lower centers to produce learning and memory. Memory is the ability to hold a thought in mind or to recall events from the past, ranging from a word we learned only yesterday to an early emotional experience that has shaped our lives. Learning takes place when we retain and use past memories. Types of Memory We have all tried to remember a seven-digit telephone number for a short time. If we say we are trying to keep it in the forefront of our brain, we are exactly correct. The prefrontal area, active during short-term memory, lies just posterior to our forehead! There are some telephone numbers that we have memorized. In other words, they have gone into long-term memory. Think of a telephone number you know by heart, and try to bring it to mind without also thinking about the place or person associated with that number. Most likely you cannot. Typically, long-term memory is a mixture of what is called semantic memory (numbers, words, etc.) and episodic memory (persons, events, etc.). Skill memory is another type of memory that can exist independent of episodic memory. Skill memory is involved in performing motor activities such as riding a bike or playing ice hockey. When a person first learns a skill, more areas of the cerebral cortex are involved than after the skill is perfected. In other words, you have to think about what you are doing when you learn a skill, but later the actions become automatic. Skill memory involves all the motor areas of the cerebrum below the level of consciousness. Long-Term Memory Storage and Retrieval Our long-term memories are apparently stored in bits and pieces throughout the sensory association areas of the cerebral cortex. Visual perceptions are stored in the vision association area, sounds are stored in the auditory association area, and so forth. As previously mentioned, the hippocampus serves as a bridge between the sensory association areas (where memories are stored) and the prefrontal area (where memories are used). The prefrontal area communicates with the hippocampus when memories are stored and when these memories are brought to mind. Some memories are emotionally charged, because the amygdala seems to be responsible for fear conditioning and associating danger with sensory stimuli received from various parts of the brain.Page 294 SCIENCE IN YOUR LIFE What is amnesia? Amnesia results from disruption of the memory pathways and can be temporary or permanent. In anterograde amnesia, injury to the limbic system separates long-term memories of events that occurred prior to the injury from events that occur in the here and now. An affected person might carry on a conversation about past events (memories of a long-ago birthday) but be unable to recall a breakfast menu from that morning. In retrograde amnesia, a blow to the head or similar injury abolishes all memories for a variable time before the injury. For example, a head injury occurring during a car accident may abolish all memories from hours to days prior to the accident. Long-Term Potentiation Though it is helpful to know the memory functions of various portions of the brain, an important step toward curing mental disorders is understanding memory on the cellular level. After synapses have been used intensively for a short time, they release more neurotransmitters than before. This phenomenon, called long-term potentiation, may be involved in memory storage. Language and Speech Language depends on semantic memory. Therefore, we would expect some of the same areas in the brain to be involved in both memory and language. Any disruption of these pathways could contribute to an inability to comprehend our environment and use speech correctly. Seeing and hearing words depends on sensory centers in the occipital and temporal lobes, respectively. Damage to Wernicke’s area (see Section 14.2) results in the inability to comprehend speech. Damage to Broca’s area, on the other hand, results in the inability to speak and write. The functions of the visual cortex, Wernicke’s area, and Broca’s area are shown in Figure 14.14. Figure 14.14 The areas of the brain involved in reading. These functional images were captured by a high-speed computer during a PET (positron-emission tomography) scan of the brain. A radioactively labeled solution is injected into the subject, and then the subject is asked to perform certain activities. Cross-sectional images of the brain generated by the computer reveal where activity is occurring because the solution is preferentially taken up by active brain tissue and not by inactive brain tissue. These PET images show the cortical pathway for reading words and then speaking them. Red indicates the most active areas of the brain, and blue indicates the least active areas. (all): ©Marcus Raichle One interesting aside pertaining to language and speech is the recognition that the left brain and the right brain may have different functions. Recall that the left hemisphere contains both Broca’s area and Wernicke’s area (see Section 14.2). As you might expect, it appears that the left hemisphere plays a role of great importance in language functions. The role of the isolated left hemisphere can be studied in patients after surgery to sever the corpus callosum. This procedure is used for seizure control in patients with epilepsy. After surgery, the patient is termed “split brain,” because there is no longer direct communication between the two cerebral hemispheres. If a split-brain individual views an object with only the right eye, its image will be sent only to the right hemisphere. This person will be able to choose the proper object for a particular use—scissors to cut paper, for example—but will be unable to name that object. Researchers now believe that the hemispheres process the same information differently. The left hemisphere is more global, whereas the right hemisphere is more specific in its approach. However, research also indicates that the classification of “right-brained” versus “left-brained” for individuals is probably not an accurate indication of an individual’s brain activity. CHECK YOUR PROGRESS 14.3 Summarize the function of the limbic system. Answer A group of brain structures that blends primitive emotions and higher mental functions into a united whole. List what limbic system structures are involved in the fight-or-flight reaction, learning, and long-term memory. Answer Amygdala—fight-or-flight; hippocampus—learning and memory. The hippocampus acts as a bridge between the sensory association areas of the cerebral cortex where memories are stored long term and the prefrontal areas of the cortex where memories are used. Describe the relationship between the left and right sides of the brain and language and speech. Answer Wernicke’s area and Broca’s area in the left hemisphere are related to speech, comprehension, and writing. The right hemisphere is associated with more nonverbal and creative functions. CONNECTING THE CONCEPTS For more information on these topics, refer to the following discussion: Section 18.5 examines the effects of aging on the body, including the nervous system.

Answer 62

Check out the pic

Answer 63

14.4 Peripheral Nervous System Learning Outcomes

Answer 64

Neurons are best classified according to:

Answer 65

14.4 The Peripheral Nervous System LEARNING OUTCOMES Upon completion of this section you should be able to Describe the series of events during a spinal reflex. Distinguish between the somatic and autonomic divisions of the peripheral nervous system. Distinguish between the sympathetic and parasympathetic divisions of the autonomic division.

Answer 66

* integration occurs and * where memories are stored. * Anterior to the primary motor area is a premotor area. The premotor area **organizes motor functions** for skilled motor activities, such as walking and talking at the same time. * Next, the **primary motor area** sends signals to the cerebellum, which integrates them. A momentary lack of oxygen during birth can damage the motor areas of the cerebral cortex, resulting in cerebral palsy, a condition characterized by a spastic weakness of the arms and legs. * The **somatosensory association area**, located just posterior to the primary somatosensory area, **processes and analyzes sensory information from the skin and muscles.** The visual association area in the occipital lobe associates new visual information with stored visual memories. It might “decide,” for example, if we have seen a face, scene, or symbol before. The auditory association area in the temporal lobe performs the same functions with regard to sounds.

Answer 67

The nervous system

Answer 68

The Diencephalon The hypothalamus and thalamus are in the diencephalon, a region that encircles the third ventricle. The hypothalamus forms the floor of the third ventricle. The hypothalamus is an integrating center that helps maintain homeostasis. It regulates hunger, sleep, thirst, body temperature, and water balance. The hypothalamus controls the pituitary gland and thereby serves as a link between the nervous and endocrine systems. The thalamus consists of two masses of gray matter located in the sides and roof of the third ventricle. The thalamus is on the receiving end for all sensory input except the sense of smell. Visual, auditory, and somatosensory information arrives at the thalamus via the cranial nerves and tracts from the spinal cord. The thalamus integrates this information and sends it on to the appropriate portions of the cerebrum. The thalamus is involved in arousal of the cerebrum, and it participates in higher mental functions, such as memory and emotions. The pineal gland, which secretes the hormone melatonin, is located in the diencephalon. Presently, there is much popular interest in the role of melatonin in our daily rhythms. Some researchers believe it can help alleviate jet lag or insomnia. Scientists are also interested in the possibility that the hormone may regulate the onset of puberty.

Answer 69

* **amygdala hippocampus olfactory bulb olfactory tract hypothalamus corpus thalamus callosum** Figure 14.12 The regions of the brain associated with the limbic system. 14.3 The Limbic System and Higher Mental Functions 28 • Learning – what happens when we recall and use past memories • **Memo**ry – ability to hold a thought or to recall past events • Short-term memory – retention of information for only a few minutes 14.3 The Limbic System and Higher Mental Functions Higher mental functions 29 Higher mental functions • Long-term memory – retention of i

Answer 70

3 functions of the nervous systen 14.1 Overview of Nervous System Slides Look at them and review diagrams

Answer 71

The PNS has divisions: the somatic system and the autonomic system. The nerves in the somatic system serve the skin, skeletal muscles, and tendons (see Fig. 14.2). The somatic system sensory nerves take sensory information from external sensory receptors to the CNS. Motor commands leaving the CNS travel to skeletal muscles via somatic motor nerves. Not all somatic motor actions are voluntary. Some are automatic. Automatic responses to a stimulus in the somatic system are called reflexes. A reflex occurs quickly, without your even having to think about it. For example, a reflex may cause you to blink your eyes in response to a flash of light, without your willing it. We will study the path of a reflex, because it allows us to study in detail the path of nerve signals to and from the CNS.Page 296

Answer 72

The peripheral nervous system (PNS)

Answer 73

Describe the three types of neurons, and list the three main parts of a neuron.

Answer 74

Classified according to function, the three types of neurons are sensory neurons, interneurons, and motor neurons (Fig. 14.3). Their functions are best described relative to the CNS. A sensory neuron takes nerve signals from a sensory receptor to the CNS. Sensory receptors are special structures that detect changes in the environment.

Answer 75

Last steps after Neurotransmitter released in Synaptic Cleft- \*\* Follow process beginning to end \*\* List steps and print out and understand photos

Answer 76

**_The Cerebral Cortex,_** gray matter, myelinated.

Answer 77

Relate how the RAS aids in homeostasis.

Answer 78

1. As you are reading these words, synapses throughout your brain are organizing, integrating, and cataloging the information you take in. 2. Neurotransmitters at these synapses control the firing of countless action potentials, thus creating a network of neural circuits. 3. It is amazing to realize that all thoughts, feelings, and actions of a human are dependent on neurotransmitters in the CNS and PNS. 4. By modifying or controlling synaptic transmission, a wide variety of drugs with neurological activity, both legal pharmaceuticals and illegal drugs of abuse, can alter mood, emotional state, behavior, and personality.

Answer 79

Identify the structures of the brain and provide a function for each.

Answer 80

CHECK YOUR PROGRESS 14.3 Summarize the function of the limbic system.

Answer 81

1. **Nerve impulse** reaches the axon terminal. 2. **Calcium ions** enter the axon terminal and **stimulate** the **synaptic vesicles** to fuse with the **presynaptic membrane**; the axon terminal membrane of the first neuron. 3. **Neurotransmitters** are released and **diffuse** across the synapse, where they bind with the **postsynaptic membrane**; 4. the **dendrite/cell body membrane** on the **second neuron to inhibit** or excite the neuron.

Answer 82

1. 1. The brain: Cerebrum 2. • Cerebral hemispheres 3. • Cerebral cortex • 4. Primary motor and sensory areas of the cortex • 5. Association areas • 6. Processing centers • 7. Central white matter * 14.2 The Central Nervous System 15 *

Answer 83

CNS 14.2 Lecture Notes This is called the CEO of the brain and controls working memory.

Answer 84

Synaptic Integration Page 286 (illustrated by the green line in Fig. 14.6b) What is integration? What are excitatory and inhibitory signals?

Answer 85

Review slides 14.2: The brain: Cerebrum – The cerebral cortex Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. salivation vocalization mastication longitudinal fissure facial expression swallowing thumb, fingers, and hand forearm arm trunk pelvis thigh leg foot and toes lips upper face

Answer 86

The central nervous system • Protection for the system Slides fron Class 14.2 The Central Nervous System Supplemental material not in book 14.2 * http://droualb.faculty.mjc.edu/Lecture%20Notes/Unit%205/Meninges\_peeled\_away.jpg * Supplemental material not in book 14.2

Answer 87

SCIENCE IN YOUR LIFE Why does a stroke on the right side of the brain cause weakness or paralysis on the left side of the body? Descending motor tracts (from the primary motor area) and ascending sensory tracts (from the primary somatosensory area) cross over in the spinal cord and medulla. Motor neurons in the right cerebral hemisphere control the left side of the body and vice versa because of crossing-over. Likewise, sensation from the left half of the body travels to the right cerebral hemisphere. Destruction of brain tissue by a stroke interferes with outgoing motor signals to the opposite side of the body, as well as incoming sensory information from that side. The primary somatosensory area is just posterior to the central sulcus in the parietal lobe. Sensory information from the skin and skeletal muscles arrives here, where each part of the body is sequentially represented (Fig. 14.11b). Like the primary motor cortex, large areas of the primary sensory cortex are dedicated to those body areas with acute sensation. Once again, the face and hands require the largest proportion of the sensory cortex. Page 291Reception areas for the other primary sensations—taste, vision, hearing, and smell—are located in other areas of the cerebral cortex (see Fig. 14.10). The primary taste area in the parietal lobe (pink) accounts for taste sensations. Visual information is received by the primary visual cortex (blue) in the occipital lobe. The primary auditory area in the temporal lobe (green) accepts information from our ears. Smell sensations travel to the primary olfactory area (yellow) found on the deep surface of the frontal lobe.

Answer 88

**_two types of cells:_** 1. **neurons**: cells that transmit nerve impulses between parts of the nervous system: Classified according to function in CNS * 3 types: functions relative to CNS 1. **_sensory neurons:_** takes nerve signals **from a sensory receptor--** special structures that detect changes in the environment--**to the CNS** 2. **_interneuron_**s: can receive input **from sensory neurons and from other interneurons** in the CNS; **sum up** all the information received from other neurons before they **communicate with motor neuron**s. 3. **_motor neurons_** A sensory neuron An interneuron lies entirely within the CNS: takes nerve impulses away from the CNS to an **effector** (muscle fiber, organ, or gland)--carry out our responses to environmental changes, whether these are external or internal. Interneurons A motor neuron 2. **neuroglia** (sometimes referred to as glial cells): support and nourish neurons * greatly outnumber neurons * several types of neuroglia in the CNS, each with specific functions: * Microglia are phagocytic cells that help remove bacteria and debris, whereas * astrocytes provide metabolic and structural support directly to the neurons. * The myelin sheath is formed from the membranes of tightly spiraled neuroglia. * In the PNS, Schwann cells perform this function, leaving gaps called nodes of Ranvier. * In the CNS, neuroglia cells called oligodendrocytes form the myelin sheath. * Neuroglia (see Section 4.4) Anatomy of a Neuron

Answer 89

Drug Influence in the CNS Drug Influence on the CNS Table Summary: Table lists the names of different substances in column 1. Other information related to these substances appears in columns 2 and 3. SubstanceEffectMode of Transmission AlcoholDepressantDrink NicotineStimulantSmoked or smokeless tobacco CocaineStimulantSniffed/snorted, injected, or smoked Methamphetamine/EcstasyStimulantSmoked or pill form HeroinDepressantSniffed/snorted, injected, or smoked Marijuana/K2PsychoactiveSmoked or consumed

Answer 90

Reticular Formation

Answer 91

SUMMARIZE 14.1Overview of the Nervous System The nervous system Is divided into the central nervous system (CNS) and the peripheral nervous system (PNS). Has three functions: (1) reception of input, (2) integration of data, and (3) generation of motor output.

Answer 92

Somatic and Parasympathetic Pathways

Answer 93

Lecture Notes True or False The prefontal cortex is also a processing center in the cerebrum?

Answer 94

The Reticular Formation The reticular formation is a complex network of nuclei, which are masses of gray matter, and fibers that extends the length of the brain stem (Fig. 14.12). The reticular formation is a major component of the reticular activating system (RAS). The RAS receives sensory signals and sends them to higher centers. Motor signals received by the RAS are sent to the spinal cord. Figure 14.12 The reticular formation of the brain. The reticular formation receives and sends on motor and sensory information to various parts of the CNS. One portion, the reticular activating system (RAS) (see arrows), arouses the cerebrum and, in this way, controls alertness versus sleep. The RAS arouses the cerebrum via the thalamus and causes a person to be alert. If you want to awaken the RAS, surprise it with sudden stimuli, such as an alarm clock ringing, bright lights, smelling salts, or cold water splashed on your face. The RAS can filter out unnecessary sensory stimuli, explaining why you can study with the TV on. Similarly, the RAS allows you to take a test without noticing the sounds of the people around you—unless the sounds are particularly distracting. To inactivate the RAS, remove visual or auditory stimuli, allowing yourself to become drowsy and drop off to sleep. General anesthetics function by artificially suppressing the RAS. A severe injury to the RAS can cause a person to become comatose, from which recovery may be impossible.

Answer 95

1. consists of the brain and spinal cord. • 2. Both are protected by • * Scalp and skin • * Bones – skull and vertebral column • 1. Meninges – 3 protective membranes that wrap around CNS • 1. Cerebral spinal fluid (CSF) – space between meninges is filled with this fluid that cushions and protects the CNS • 2. Blood brain barrier (BBB) 3. 2 Meninges 1. • Dura mater • Double-layered external covering Periosteum – dense connective tissue attached to surface of the skull 2. • Meningeal layer – outer covering of the brain • Folds inward in several areas 3. \*\*\*Supplemental material not in book 3 Meninges • Arachnoid mater • Middle layer • Web-like • Pia mater • Internal layer • Clings to the surface of the brain • Many blood vessels http://droualb.faculty.mjc.edu/Lecture%20Notes/Unit%205/Meninges\_peeled\_away.jpg Supplemental material not in book 14.2 The Central Nervous System 4 Cerebrospinal Fluid (CSF) • Similar to blood plasma composition, as it is formed from blood plasma • Forms a watery cushion to protect the brain • Circulated in subarachnoid space, ventricles, and central canal of the spinal cord

Answer 96

Wernicke’s area and Broca’s area in the left hemisphere are related to speech, comprehension, and writing. The right hemisphere is associated with more nonverbal and creative functions.

Answer 97

CHECK YOUR PROGRESS 14.1 Sensory neurons take nerve signals from a sensory receptor to the CNS. Interneurons lie entirely within the CNS and communicate with other neurons. Motor neurons move nerve impulses away from the CNS to an effector. The parts are cell body, dendrites, and axon.

Answer 98

PNS Slides Peripheral Nervous System The PNS is divided into 2 systems. - Somatic division - Autonomic division

Answer 99

s – branched cells that wrap CNS nerve fibers – Produce fatty insulating coverings (myelin sheath) around nerve fibers in the CNS – Can coil around as many as 60 different fibers at one time

Answer 100

14.2 The Central Nervous System LEARNING OUTCOMES Upon completion of this section, you should be able to Identify the structures of the spinal cord and provide a function for each. Identify the structures of the brain and provide a function for each. Identify the lobes and major areas of the human brain. Distinguish between the functions of the primary motor and the primary somatosensory areas of the brain. The spinal cord and the brain make up the CNS, where sensory information is received and motor control is initiated. Both the spinal cord and the brain are protected by bone. The spinal cord is surrounded by vertebrae, and the brain is enclosed by the skull. Also, both the spinal cord and the brain are wrapped in protective Page 287membranes known as meninges (sing., meninx). Meningitis is an infection of the meninges and may be caused by either bacterial or viral pathogens. The spaces between the meninges are filled with cerebrospinal fluid, which cushions and protects the CNS. In a spinal tap (lumbar puncture), a small amount of this fluid is withdrawn from around the spinal cord for laboratory testing. Cerebrospinal fluid is also contained within the ventricles of the brain and in the central canal of the spinal cord. The brain has four ventricles, interconnecting chambers that produce and serve as a reservoir for cerebrospinal fluid (Fig. 14.7). Normally, any excess cerebrospinal fluid drains away into the cardiovascular system. However, blockages can occur. In an infant, the brain can enlarge due to cerebrospinal fluid accumulation, resulting in a condition called hydrocephalus (“water on the brain”). If cerebrospinal fluid collects in an adult, the brain cannot enlarge. Instead, it is pushed against the skull. Such situations cause severe brain damage and can be fatal unless quickly corrected. Figure 14.7 The ventricles of the brain. The brain has four ventricles. A lateral ventricle is found on each side of the brain. They join at the third ventricle. The third ventricle connects with the fourth ventricle superiorly; the central canal of the spinal cord joins the fourth ventricle inferiorly. All structures are filled with cerebrospinal fluid. a. Lateral view of ventricles seen through a transparent brain. b. Anterior view of ventricles seen through a transparent brain. The CNS is composed of two types of nervous tissue—gray matter and white matter. Gray matter contains cell bodies and short, nonmyelinated axons. White matter contains myelinated axons that run together in bundles called tracts.

Answer 101

1. Provides a means of communication between the brain and the peripheral nerves 2. center for reflex actions.

Answer 102

• 2 divisions – Central nervous system (CNS): –Brain and spinal cord –Peripheral nervous system (PNS): Nerves and ganglia (collections of cell bodies)

Answer 103

SCIENCE IN YOUR LIFE Why does a stroke on the right side of the brain cause weakness or paralysis on the left side of the body? 1. **_Descending motor tracts (from the primary motor area)_** 2. and **_ascending sensory tracts (from the primary somatosensory area)_** cross over in the spinal cord and medulla. 3. **Motor neurons** in the right cerebral hemisphere control the left side of the body and vice versa because of crossing-over. 4. Likewise, sensation from the left half of the body travels to the right cerebral hemisphere. 5. _**\*\*Destruction of brain tissue by a stroke interferes with outgoing motor signals to the opposite side of the body, as well as incoming sensory information from that side.**_

Answer 104

* A resting neuron's potential energy, much like a fully charged batter, exists because the plasma membrane is polarized: Positively charged ions are stashed outside the cell, with negatively charged ions inside. oteins and other molecules that remain inside the cell because of their size. * Study Figure 14.4a outside of the cell is positive because positively charged sodium ions (Na+) gather around the outside of the plasma membrane. 1. \*\*\*Process\*\*\*At rest, the neuron’s plasma membrane is permeable to potassium, but not to sodium. 2. Thus, positively charged potassium ions (K+) contribute to the positive charge by diffusing out of the cell to join the sodium ions. The inside of the cell is negative in relation to the exterior of the cell because of the presence of large, negatively charged pr Just like rechargeable batteries, neurons must maintain their resting potential to be able to work. To do so, neurons actively transport sodium ions out of the cell and return potassium ions to Page 284the cytoplasm. A protein carrier in the membrane, called the sodium–potassium pump, pumps sodium ions (Na+) out of the neuron and potassium ions (K+) into the neuron (see Section 3.3). This action effectively “recharges” the cell so that, like a fresh battery, it can perform work.

Answer 105

1. Sensory (afferent) division  * Nerve fibers that carry information to the central nervous system  2. Motor (efferent) division  1. Nerve fibers that carry impulses away from the central nervous system  3. Somatic nervous system = voluntary (skeletal muscles)  4. Autonomic nervous system = involuntary (cardiac and smooth muscles, glands)

Answer 106

What is Central White Matter? Where is it found? What process enables the brain to grow in size and complexity What occurs?

Answer 107

Small, ovoid cells with spiny processes, “spider-like cells” –Phagocytes from red bone marrow that monitor the health of neurons – Dispose of dead cells, invading microorganisms M

Answer 108

**_What are neuromodulators?_**

Answer 109

1. Most drug abusers take drugs that affect the neurotransmitter **dopamine** and thus artificially affect this **reward circuit** to the point that they ignore basic physical needs in favor of the drug.

Answer 110

Functional Classification of the Peripheral Nervous System

Answer 111

* I consist of **two masses of gray matter** * I live in the sides and roof of the third ventricle. * I receive end all sensory input except the sense of smell. * Visual, auditory, and somatosensory information arrives via my friends the and tracts from the spinal cord. * I integrate this information and sends it on to the appropriate portions of the \_\_\_\_\_\_\_\_\_\_\_\_\_\_ * In fact, I am very involved in arousal of _______ and * I am quite fancy as I participate in higher mental functions, such as **memory and emotions.**

Answer 112

A lipid covering on long axons that acts to increase the speed of nerve impulse conduction, insulation for both CNS and PNS, and regeneration in the PNS • Schwann cells – neuroglia that make up the myelin sheath in the PNS • Oligodendrocytes- neuroglia that make up the myelin sheath in the CNS • Nodes of Ranvier – gaps between myelination on the axons • Saltatory conduction – conduction of the nerve impulse from node to node

Answer 113

Cerebrospinal fluid abnormalities in children and adults

Answer 114

CNS **_Neurons:_** **_Resting Potential_** Page 283- See, Download and Understand and Study 14.4 a As Figure 14.4a See Animation Tutorial: Neuron Action Potentials How the Sodium–Potassium Pump Works Like a battery, the neuron’s resting potential energy can be measured in volts. Whereas a D-size flashlight battery has 1.5 volts, a nerve cell typically has 0.070 volt, or 70 millivolts (mV), of stored energy (Fig. 14.4a). By convention, the voltage measurement is always a negative number. This is because scientists compare the inside of the cell—where negatively charged proteins and other large molecules are clustered—to the outside of the cell—where positively charged sodium and potassium ions are gathered. Figure 14.4 Generation of an action potential. a. Resting potential occurs when a neuron is not conducting a nerve impulse. During an action potential, (b) the stimulus causes the cell to reach its threshold. c. Depolarization is followed by (d) repolarization. e. A graph depicting the generation of an action potential.shows,

Answer 115

The Brain Stem * The tracts cross in the **brain stem,** which contains the **midbrain, the pons, and the medulla oblongata** (see Fig. 14.9a). * The midbrain acts as a relay station for tracts passing between the cerebrum and Page 292the spinal cord or cerebellum. It also has reflex centers for visual, auditory, and tactile responses. * The **pons (“bridge” in Latin)** contains bundles of axons traveling between the cerebellum and the rest of the CNS. * In addition, the pons functions with the medulla oblongata to regulate breathing rate. * **Reflex centers** in the pons coordinate head movements in response to visual and auditory stimuli. * The ***medulla oblongata** c*ontains a number of reflex centers for regulating heartbeat, breathing, and vasoconstriction (blood pressure). It also contains the reflex centers for vomiting, coughing, sneezing, hiccuping, and swallowing. The medulla oblongata lies just superior to the spinal cord, and it contains tracts that ascend or descend between the spinal cord and higher brain centers. Recall that tracts are groups of axons that travel together. Ascending tracts convey sensory information. Motor information is transmitted on descending tracts.

Answer 116

The Cerebral Cortex The cerebral cortex is a thin, highly convoluted outer layer of gray matter that covers the cerebral hemispheres. Recall that gray matter consists of neurons whose axons are not myelinated. The cerebral cortex contains over 1 billion cell bodies and is the region of the brain that accounts for sensation, voluntary movement, and all the thought processes we associate with consciousness.

Answer 117

14.3 The Limbic System and Higher Mental Functions LEARNING OUTCOMES Upon completion of this section, you should be able to Identify the structures of the limbic system. Explain how the limbic system is involved in memory, language, and speech. Summarize the types of memory associated with the limbic system. The limbic system integrates our emotions (fear, joy, sadness) with our higher mental functions (reason, memory). Because of the limbic system, activities such as sexual behavior and eating seem pleasurable, and mental stress can cause high blood pressure. Limbic System The limbic system is an evolutionary ancient group of linked structures deep within the cerebrum. It is a functional grouping rather than an anatomical one (Fig. 14.13). The limbic system blends primitive emotions and higher mental functions into a united whole. As already noted, it accounts for why activities such as sexual behavior and eating seem pleasurable. Conversely, unpleasant sensations or emotions (pain, frustration, hatred, despair) are translated by the limbic system into a stress response. Figure 14.13 The regions of the brain associated with the limbic system. In the limbic system (purple), structures deep within each cerebral hemisphere and surrounding the diencephalon join higher mental functions, such as reasoning, with more primitive feelings, such as fear and pleasure. Therefore, primitive feelings can influence our behavior, but reason can also keep them in check. Two significant structures in the limbic system are the amygdala and the hippocampus. The amygdala, in particular, can cause experiences to have emotional overtones, and it creates the sensation Page 293of fear. This center can use past knowledge fed to it by association areas to assess a current situation. If necessary, the amygdala can trigger the fight-or-flight reaction. So if you are out late at night and you turn to see someone in a ski mask following you, the amygdala may immediately cause you to start running. The frontal cortex can override the limbic system, cause you to rethink the situation, and prevent you from acting out strong reactions. The hippocampus is believed to play a crucial role in learning and memory. The hippocampal region acts as an information gateway during the learning process. It determines what information about the world is to be sent to memory and how this information is to be encoded and stored by other regions in the brain. Most likely, the hippocampus can communicate with the frontal cortex, because we know that memories are an important part of our decision-making processes. Higher Mental Functions As in other areas of biological research, brain research has progressed due to technological breakthroughs. Neuroscientists now have a wide range of techniques at their disposal for studying the human brain, including modern technologies that allow us to record its functioning. Memory and Learning Just as the connecting tracts of the corpus callosum are evidence that the two cerebral hemispheres work together, so the limbic system indicates that cortical areas may work with lower centers to produce learning and memory. Memory is the ability to hold a thought in mind or to recall events from the past, ranging from a word we learned only yesterday to an early emotional experience that has shaped our lives. Learning takes place when we retain and use past memories. Types of Memory We have all tried to remember a seven-digit telephone number for a short time. If we say we are trying to keep it in the forefront of our brain, we are exactly correct. The prefrontal area, active during short-term memory, lies just posterior to our forehead! There are some telephone numbers that we have memorized. In other words, they have gone into long-term memory. Think of a telephone number you know by heart, and try to bring it to mind without also thinking about the place or person associated with that number. Most likely you cannot. Typically, long-term memory is a mixture of what is called semantic memory (numbers, words, etc.) and episodic memory (persons, events, etc.). Skill memory is another type of memory that can exist independent of episodic memory. Skill memory is involved in performing motor activities such as riding a bike or playing ice hockey. When a person first learns a skill, more areas of the cerebral cortex are involved than after the skill is perfected. In other words, you have to think about what you are doing when you learn a skill, but later the actions become automatic. Skill memory involves all the motor areas of the cerebrum below the level of consciousness. Long-Term Memory Storage and Retrieval Our long-term memories are apparently stored in bits and pieces throughout the sensory association areas of the cerebral cortex. Visual perceptions are stored in the vision association area, sounds are stored in the auditory association area, and so forth. As previously mentioned, the hippocampus serves as a bridge between the sensory association areas (where memories are stored) and the prefrontal area (where memories are used). The prefrontal area communicates with the hippocampus when memories are stored and when these memories are brought to mind. Some memories are emotionally charged, because the amygdala seems to be responsible for fear conditioning and associating danger with sensory stimuli received from various parts of the brain.Page 294 SCIENCE IN YOUR LIFE What is amnesia? Amnesia results from disruption of the memory pathways and can be temporary or permanent. In anterograde amnesia, injury to the limbic system separates long-term memories of events that occurred prior to the injury from events that occur in the here and now. An affected person might carry on a conversation about past events (memories of a long-ago birthday) but be unable to recall a breakfast menu from that morning. In retrograde amnesia, a blow to the head or similar injury abolishes all memories for a variable time before the injury. For example, a head injury occurring during a car accident may abolish all memories from hours to days prior to the accident. Long-Term Potentiation Though it is helpful to know the memory functions of various portions of the brain, an important step toward curing mental disorders is understanding memory on the cellular level. After synapses have been used intensively for a short time, they release more neurotransmitters than before. This phenomenon, called long-term potentiation, may be involved in memory storage. Language and Speech Language depends on semantic memory. Therefore, we would expect some of the same areas in the brain to be involved in both memory and language. Any disruption of these pathways could contribute to an inability to comprehend our environment and use speech correctly. Seeing and hearing words depends on sensory centers in the occipital and temporal lobes, respectively. Damage to Wernicke’s area (see Section 14.2) results in the inability to comprehend speech. Damage to Broca’s area, on the other hand, results in the inability to speak and write. The functions of the visual cortex, Wernicke’s area, and Broca’s area are shown in Figure 14.14. Figure 14.14 The areas of the brain involved in reading. These functional images were captured by a high-speed computer during a PET (positron-emission tomography) scan of the brain. A radioactively labeled solution is injected into the subject, and then the subject is asked to perform certain activities. Cross-sectional images of the brain generated by the computer reveal where activity is occurring because the solution is preferentially taken up by active brain tissue and not by inactive brain tissue. These PET images show the cortical pathway for reading words and then speaking them. Red indicates the most active areas of the brain, and blue indicates the least active areas. (all): ©Marcus Raichle One interesting aside pertaining to language and speech is the recognition that the left brain and the right brain may have different functions. Recall that the left hemisphere contains both Broca’s area and Wernicke’s area (see Section 14.2). As you might expect, it appears that the left hemisphere plays a role of great importance in language functions. The role of the isolated left hemisphere can be studied in patients after surgery to sever the corpus callosum. This procedure is used for seizure control in patients with epilepsy. After surgery, the patient is termed “split brain,” because there is no longer direct communication between the two cerebral hemispheres. If a split-brain individual views an object with only the right eye, its image will be sent only to the right hemisphere. This person will be able to choose the proper object for a particular use—scissors to cut paper, for example—but will be unable to name that object. Researchers now believe that the hemispheres process the same information differently. The left hemisphere is more global, whereas the right hemisphere is more specific in its approach. However, research also indicates that the classification of “right-brained” versus “left-brained” for individuals is probably not an accurate indication of an individual’s brain activity. CHECK YOUR PROGRESS 14.3 Summarize the function of the limbic system. Answer A group of brain structures that blends primitive emotions and higher mental functions into a united whole. List what limbic system structures are involved in the fight-or-flight reaction, learning, and long-term memory. Answer Amygdala—fight-or-flight; hippocampus—learning and memory. The hippocampus acts as a bridge between the sensory association areas of the cerebral cortex where memories are stored long term and the prefrontal areas of the cortex where memories are used. Describe the relationship between the left and right sides of the brain and language and speech. Answer Wernicke’s area and Broca’s area in the left hemisphere are related to speech, comprehension, and writing. The right hemisphere is associated with more nonverbal and creative functions. CONNECTING THE CONCEPTS For more information on these topics, refer to the following discussion: Section 18.5 examines the effects of aging on the body, including the nervous system.

Answer 118

* * extends from the base of the brain through a large opening in the skull called the foramen magnum (see Fig. 12.4). * From the foramen magnum, the spinal cord proceeds inferiorly in the vertebral canal. * * Structure of the Spinal Cord * A cross-section of the spinal cord (Fig. 14.8a) shows a 1. central canal, 2. gray matter, and 3. white matter. *

Answer 119

1. In myelinated fibers, an action potential at one node of Ranvier causes an action potential at the next node, jumping over the entire myelin-coated portion of the axon. 1. This type of conduction is called saltatory conduction (saltatio is a Latin word that means “to jump”) and is much faster. 2. In thick, myelinated fibers, the rate of transmission is more than 100 m/s. 3. Regardless of whether an axon is myelinated or not, its action potentials are self-propagating. 4. Each action potential generates another, along the entire length of the axon. 2. Like the action potential itself, conduction of an action potential is an all-or-none event—either an axon conducts its action potential or it does not. * The intensity of a message is determined by how many action potentials are generated within a given time. * An axon can conduct a volley of action potentials very quickly, because only a small number of ions are exchanged with each action potential. * Once the action potential is complete, the ions are rapidly restored to their proper place through the action of the sodium–potassium pump. 3. As soon as the action potential has passed by each successive portion of an axon, that portion undergoes a short refractory period, during which it is unable to conduct an action potential. * This ensures the one-way direction of a signal from the cell body down the length of the axon to the axon terminal. It is interesting to note that all functions of the nervous system, from our deepest emotions to our highest reasoning abilities, are dependent on the conduction of nerve signals.

Answer 120

The nerve impulse: Resting potential (RP) • Resting potential – when the axon is not conducting a nerve impulse (when the axon is “at rest”) • More positive ions outside than inside the membrane • Negative charge of -70 mV inside the axon • More Na+ outside than inside • More K+ inside than outside 14.1 Overview of the Nervous System

Answer 121

1) thalamus 2) cranial nerve 3) cerebrum

Answer 122

The Brain The human brain has been called the last great frontier of biology. The goal of modern neuroscience is to understand the structure and function of the brain’s various parts so well that it will be possible to prevent or correct the thousands of mental disorders that rob humans of a normal life. This section gives only a glimpse of what is known about the brain and the modern avenues of research. We discuss the parts of the brain with reference to the cerebrum, the diencephalon, the cerebellum, and the brain stem. The brain’s four ventricles (see Fig. 14.7) are called, in turn, the two lateral ventricles, the third ventricle, and the fourth ventricle. It may be helpful for you to associate the cerebrum with the two lateral ventricles, the diencephalon with the third ventricle, and the brain stem and cerebellum with the fourth ventricle (Fig. 14.9a). Figure 14.9 The human brain. a. The cerebrum is the largest part of the brain in humans. b. Viewed from above, the cerebrum has left and right cerebral hemispheres. The hemispheres are connected by the corpus callosum. (b): ©McGraw-Hill Education; photo and dissection by Christine Eckel The Cerebrum The cerebrum is the largest portion of the brain in mammals, including humans. The cerebrum is the last center to receive sensory input and carry out integration before commanding voluntary motor responses. It communicates with and coordinates the activities of the other parts of the brain. Cerebral Hemispheres Just as the human body has two halves, so does the cerebrum. These halves are called the left and right cerebral hemispheres (Fig. 14.9b). A deep groove called the longitudinal fissure divides the left and right cerebral hemispheres. The two cerebral hemispheres communicate via the corpus callosum, an extensive bridge of nerve tracts. Page 289The characteristic appearance of the cerebrum is the result of thick folds, called gyri (sing., gyrus) separated by shallow grooves called sulci (sing., sulcus). The sulci divide each hemisphere into lobes (Fig. 14.10). The frontal lobe is the most anterior of the lobes (directly behind the forehead). The parietal lobe is posterior to the frontal lobe. The occipital lobe is posterior to the parietal lobe (at the rear of the head). The temporal lobe lies inferior to the frontal and parietal lobes (at the temple and the ear). Figure 14.10 The lobes of the cerebral hemispheres. Each cerebral hemisphere is divided into four lobes: frontal, parietal, temporal, and occipital. Centers in the frontal lobe control movement and higher reasoning, as well as the smell sensation. Somatic sensing is carried out by parietal lobe neurons, and those of the temporal lobe receive sound information. Visual information is received and processed in the occipital lobe. The Cerebral Cortex The cerebral cortex is a thin, highly convoluted outer layer of gray matter that covers the cerebral hemispheres. Recall that gray matter consists of neurons whose axons are not myelinated. The cerebral cortex contains over 1 billion cell bodies and is the region of the brain that accounts for sensation, voluntary movement, and all the thought processes we associate with consciousness.

Answer 123

The spinal cord extends from the base of the brain through a large opening in the skull called the foramen magnum (see Fig. 12.4). From the foramen magnum, the spinal cord proceeds inferiorly in the vertebral canal.

Answer 124

Primary Somatosensory Areas

Answer 125

1. protected by bone * The spinal cord is surrounded by vertebrae, and the brain is enclosed by the skull. 2. Also, both the spinal cord and the brain are wrapped in protective membranes known as **meninges (**sing., meninx).

Answer 126

**reception and processing** of *sensory information* from both the **external and the internal environments.** The nervous system hao major divisions.s tw The major structures of the nervous system are shown in Figure 14.1.

Answer 127

**_Diencephalon_** * a region that encircles the third ventricle. 1. The **hypothalamus** * forms the floor of the third ventricle. * integrating center that helps maintain homeostasis. 1. It regulates hunger, sleep, thirst, body temperature, and water balance. * \*\*\*_**controls the pituitary gland serves as a link between the nervous and endocrine systems\***_\*\* 2. The **thalamus** * two masses of gray matter * sides and roof of the third ventricle. * receiving end for **_all sensory input except the sense of smell._** * Visual, auditory, and somatosensory information arrives at the thalamus via the **cranial nerves and tracts** from the spinal cord. * integrates this information and sends it on to the appropriate portions of the **cerebrum.** * The thalamus is involved in **arousal** of the cerebrum, and it participates in \*\* **higher mental functions, such as memory and emotions.\*\*\*** The pineal gland, which secretes the hormone melatonin, is located in the diencephalon. Presently, there is much popular interest in the role of melatonin in our daily rhythms. Some researchers believe it can help alleviate jet lag or insomnia. Scientists are also interested in the possibility that the hormone may regulate the onset of puberty. The Cerebellum The cerebellum lies under the occipital lobe of the cerebrum and is separated from the brain stem by the fourth ventricle. The cerebellum has two portions joined by a narrow median portion. Each portion is primarily composed of white matter. In a longitudinal section, the white matter has a treelike pattern called arbor vitae. Overlying the white matter is a thin layer of gray matter that forms a series of complex folds. The cerebellum receives sensory input from the eyes, ears, joints, and muscles about the present position of body parts. It also receives motor output from the cerebral cortex about where these parts should be located. After integrating this information, the cerebellum sends motor signals by way of the brain stem to the skeletal muscles. In this way, the cerebellum maintains posture and balance. It also ensures that all the muscles work together to produce smooth, coordinated, voluntary movements. The cerebellum assists in the learning of new motor skills, such as playing the piano or hitting a baseball. The Brain Stem The tracts cross in the brain stem, which contains the midbrain, the pons, and the medulla oblongata (see Fig. 14.9a). The midbrain acts as a relay station for tracts passing between the cerebrum and Page 292the spinal cord or cerebellum. It also has reflex centers for visual, auditory, and tactile responses. The pons (“bridge” in Latin) contains bundles of axons traveling between the cerebellum and the rest of the CNS. In addition, the pons functions with the medulla oblongata to regulate breathing rate. Reflex centers in the pons coordinate head movements in response to visual and auditory stimuli. The medulla oblongata contains a number of reflex centers for regulating heartbeat, breathing, and vasoconstriction (blood pressure). It also contains the reflex centers for vomiting, coughing, sneezing, hiccuping, and swallowing. The medulla oblongata lies just superior to the spinal cord, and it contains tracts that ascend or descend between the spinal cord and higher brain centers. Recall that tracts are groups of axons that travel together. Ascending tracts convey sensory information. Motor information is transmitted on descending tracts. The Reticular Formation The reticular formation is a complex network of nuclei, which are masses of gray matter, and fibers that extends the length of the brain stem (Fig. 14.12). The reticular formation is a major component of the reticular activating system (RAS). The RAS receives sensory signals and sends them to higher centers. Motor signals received by the RAS are sent to the spinal cord. Figure 14.12 The reticular formation of the brain. The reticular formation receives and sends on motor and sensory information to various parts of the CNS. One portion, the reticular activating system (RAS) (see arrows), arouses the cerebrum and, in this way, controls alertness versus sleep. The RAS arouses the cerebrum via the thalamus and causes a person to be alert. If you want to awaken the RAS, surprise it with sudden stimuli, such as an alarm clock ringing, bright lights, smelling salts, or cold water splashed on your face. The RAS can filter out unnecessary sensory stimuli, explaining why you can study with the TV on. Similarly, the RAS allows you to take a test without noticing the sounds of the people around you—unless the sounds are particularly distracting. To inactivate the RAS, remove visual or auditory stimuli, allowing yourself to become drowsy and drop off to sleep. General anesthetics function by artificially suppressing the RAS. A severe injury to the RAS can cause a person to become comatose, from which recovery may be impossible. CHECK YOUR PROGRESS 14.2 List the functions of the spinal cord. Answer Provides a means of communication between the brain and the peripheral nerves, and is the center for reflex actions. Summarize the major regions of the brain and describe the general function of each. Answer Cerebrum—largest part of the brain, integrates sensory inputs and coordinates the activities of the other parts of the brain; diencephalon—contains the hypothalamus and thalamus, maintains homeostasis, receives sensory input; cerebellum—sends out motor impulses by way of the brain stem to the skeletal muscles, produces smooth, coordinated voluntary movements; brain stem—contains the midbrain, pons, and medulla oblongata, acts as a relay station, and the medulla has reflex centers. Relate how the RAS aids in homeostasis. Answer The RAS regulates a person’s alertness, relays sensory signals to higher centers, and filters out unnecessary stimuli, which are important functions in being properly responsive to one’s environment. CONNECTING THE CONCEPTS For more information on the central nervous system, refer to the following discussions: Section 10.5 examines how the central nervous system controls breathing. Section 18.5 explores how aging and diseases such as Alzheimer disease influence the brain. Sections 23.3 and 23.4 outline how the size of the brain has changed over the course of human evolution.

Answer 128

What are the tracts crossing in the ___________________________ that contain the midbrain, \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, and \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_. See and download diagram 14.9, (see Fig. 14.9a). Page 292 What do ascending and descending tracts do? What are the functions of each part of the brain stem?

Answer 129

* acetylcholine: 1. essential for memory circuits in the limbic system * dopamine 1. in the basal nuclei it helps coordinate movements, also plays a role in mood regulation * GABA: abundant inhibitory neurotransmitter in the CNS * norepinephrine: important to dreaming, waking, and mood * serotonin: thermoregulation, sleeping, emotions and perception.

Answer 130

Biology Today Nerve Regeneration and Stem Cells

Answer 131

These centers ## Footnote of the cortex receive information from the other association areas and perform higher-level analytical functions. The prefrontal area, an association area in the frontal lobe, receives information from the other association areas and uses this information to reason and plan our actions. Integration in this area accounts for our most cherished human abilities. Reasoning, critical thinking, and formulating appropriate behaviors are possible because of integration carried out in the prefrontal area. The unique ability of humans to speak is partially dependent on two processing centers found only in the left cerebral cortex. Wernicke’s area is located in the posterior part of the left temporal lobe. Broca’s area is located in the left frontal lobe. Broca’s area is just anterior to the portion of the primary motor area for speech musculature (lips, tongue, larynx, and so forth) (see Fig. 14.10). Wernicke’s area helps us understand both the written and the spoken word and sends the information to Broca’s area. Broca’s area adds grammatical refinements and directs the primary motor area to stimulate the appropriate muscles for speaking and writing.

Answer 132

Page 288 Reflex Actions The spinal cord is the center for thousands of reflex arcs (see Fig. 14.17). A stimulus causes sensory receptors to generate signals that travel in sensory axons to the spinal cord. Interneurons integrate the incoming data and relay signals to motor neurons. A response to the stimulus occurs when motor axons cause skeletal muscles to contract. Motor neurons in a reflex arc may also affect smooth muscle, organs, or glands. Each interneuron in the spinal cord synapses with numerous other neurons. From there, interneurons send signals to other interneurons and motor neurons. Similarly, the spinal cord creates reflex arcs for the internal organs. For example, when blood pressure falls, internal receptors in the carotid arteries and aorta generate nerve signals that pass through sensory fibers to the cord and then up an ascending tract to a cardiovascular center in the brain. Thereafter, nerve signals pass down a descending tract to the spinal cord. Motor signals then cause blood vessels to constrict, so that the blood pressure rises.

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5 The nerve impulse: action potential • Action potential – rapid change in the axon membrane; a nerve impulse– threshold is -55mV • Sodium gates open letting Na+ in • Depolarization occurs (-70mV to threshold-55mV) • Interior of axon loses negative charge (+35mV) • Potassium gates open letting K+ out • Repolarization occurs • Interior of axon regains negative charge (-70mV) • Wave of depolarization/repolarization travels down the axon. • Resting potential is restored by moving potassium inside and sodium outside 14.1 Overview of the nervous system

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What is the hypothalamus?

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The RAS regulates a person’s alertness, relays sensory signals to higher centers, and filters out unnecessary stimuli, which are important functions in being properly responsive to one’s environment.

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Language and Speech and Attending Issues Explore imagery The functions of the visual cortex, Wernicke’s area, and Broca’s area are shown in Figure 14.14. Figure 14.14 The areas of the brain involved in reading. These functional images were captured by a high-speed computer during a PET (positron-emission tomography) scan of the brain. A radioactively labeled solution is injected into the subject, and then the subject is asked to perform certain activities. Cross-sectional images of the brain generated by the computer reveal where activity is occurring because the solution is preferentially taken up by active brain tissue and not by inactive brain tissue. These PET images show the cortical pathway for reading words and then speaking them. Red indicates the most active areas of the brain, and blue indicates the least active areas. Review

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Nerve Impulse

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* Nerve Impulse * Sodium Gates Open See download and study 14.4c (Fig. 14.4d). 1. Neural Transmission: Resting Membrane Potential and Propagation 2. Graph of an Action Potential 3. To visualize such rapid fluctuations in voltage across the axonal membrane, researchers generally find it useful to plot the voltage changes over time (Fig. 14.4e). During depolarization, the voltage increases from −70 mV to −55 mV to between +30 and +35 mV as sodium ions move to the inside of the axon. In repolarization, the opposite change occurs when potassium ions leave the axon. The entire process is very rapid, requiring only 3 to 4 milliseconds (ms) to complete. 4. \*\*\*Proccess, know steps- short answers\*\* study slides

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Ependymal Cells

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Sensory receptors in skin and other organs respond to external and internal stimuli by generating nerve signals that travel by way of the PNS to the CNS. For example, if you smell baking cookies, olfactory (smell) receptors in the nose use the PNS to transmit that information to the CNS.The CNS performs information processing and integration, summing up the input it receives from all over the body. The CNS reviews the information, stores the information as memories, and creates the appropriate motor responses. The smell of those baking cookies evokes memories of their taste. The CNS generates motor output. Nerve signals from the CNS go by way of the PNS to the muscles, glands, and organs, all in response to the cookies. Signals to the salivary glands make you salivate. Your stomach generates the acid and enzymes Page 281needed to digest the cookies—even before you’ve had a bite. The CNS also coordinates the movement of your arms and hands as you reach for the cookies.

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Association Areas are where 1) 2) These are the association centers:

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the somatic system and the autonomic nervous system **_Somatic System_** * The nerves serve the * skin, * skeletal muscles, and * tendons * nerves take sensory information from **external sensory receptor**s to the **CNS.** * Motor commands leaving the CNS travel to **skeletal muscles via somatic motor nerves.** 1. Not all somatic motor actions are voluntary. Some are automatic. 2. Automatic responses to a stimulus in the somatic system are called **reflexes.** A reflex occurs quickly, without your even having to think about it. 1. For example, a reflex may cause you to blink your eyes in response to a flash of light, without your willing it. We will study the path of a reflex, because it allows us to study in detail the path of nerve signals to and from the CNS.Page 296

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**_primary somatosensory area_** **_see and download:_** (Fig. 14.11b), Page 291

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Master controlling and communicating system of the body • Sensory input – gathering information • To monitor changes (stimuli) occurring inside and outside the body • Integration • To process and interpret sensory input and decide if action is needed • Motor output • A response to integrated stimuli • The response activates muscles or glands 14.1 Overview of the nervous system T

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Gate Control Theory of Pain - Spinal Cord Functions

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1. axons outside the brain and spinal cord can regenerate—but axons inside these organs cannot After injury, axons in the human central nervous system (CNS) degenerate, resulting in permanent loss of nervous function. 2. Interestingly, about 90% of the cells in the brain and the spinal cord are not even neurons. They are neuroglia cells. 3. In nerves outside the brain and spinal cord, the neuroglia cells are Schwann cells that help axons regenerate. The neuroglia cells in the CNS include microglial cells, oligodendrocytes, and astrocytes, and they inhibit axon regeneration 4. 5. **The spinal cord contains its own stem cells.** When the spinal cord is injured in experimental animals, these stem cells proliferate. But instead of becoming functional neurons, they become neuroglia cells. Researchers are trying to understand the process that triggers the stem cells to become neuroglia cells. In the future, this understanding would allow manipulation of stem cells into neurons. 6. In early experiments with neural stem cells in the laboratory, scientists at Johns Hopkins University caused embryonic stem (ES) cells to differentiate into spinal cord motor neurons, the type of nerve cell that causes muscles to contract. The motor neurons then produced axons. When grown in the same dish with muscle cells, the motor neurons formed neuromuscular junctions and even caused muscle contractions. The cells were then transplanted into the spinal cords of rats with spinal cord injuries. Some of the transplanted cells survived for longer than a month within the spinal cord. However, no improvement in symptoms was seen and no functional neuron connections were made. 7. In later experiments by the same research group, paralyzed rats were first treated with drugs and nerve growth factors to overcome inhibition from the central nervous system. These techniques significantly increased the success of the transplanted neurons. Amazingly, axons of transplanted neurons reached the muscles, formed neuromuscular junctions, and provided partial relief from the paralysis. Research is being done on the use of both the body’s own stem cells and laboratory-grown stem cells to repair damaged CNS neurons. Though many questions remain, the current results are promising. 8. Questions to Consider 9. What is the likely reason neurons cannot simply be transplanted from other areas of the body? 10. How might this research also help patients who suffer from neurodegenerative diseases, such as Parkinson disease? 11. Long axons tend to have a myelin sheath, but short axons do not. The gray matter of the CNS is gray because it contains no myelinated axons; the white matter of the CNS is white because it does. In the PNS, myelin gives nerve fibers their white, glistening appearance and serves as an excellent insulator. When the myelin breaks down, as happens in multiple sclerosis (MS) (see chapter opener), then it becomes more difficult for the neurons to transmit information. In effect, MS “short-circuits” the nervous system. The myelin sheath also plays an important role in nerve regeneration within the PNS. If an axon is accidentally severed, the myelin sheath remains and serves as a passageway for new fiber growth.

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Though the majority of each cerebral hemisphere is composed of tracts, there are masses of gray matter deep within the white matter. These basal nuclei integrate motor commands to ensure that the proper muscle groups are stimulated or inhibited. Integration ensures that movements are coordinated and smooth. Parkinson disease (see Section 18.5) is believed to be caused by degeneration of specific neurons in the basal nuclei.

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1. last great frontier of biology. 2. parts of the brain with reference to the 1. cerebrum- 2 lateral ventricles 2. the diencephalon- third ventricle 3. the cerebellum, fourth ventricle 4. brain stem- 4th 3. ***_Figure 14.9_*** The human brain. a. The cerebrum is the largest part of the brain in humans. b. Viewed from above, the cerebrum has left and right cerebral hemispheres. The hemispheres are connected by the corpus callosum.

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Physiology of a Neuron Nerve signals are the electrochemical changes that convey information within the nervous system. In the past, nerve signals could be studied only in neurons that had been removed from the body or from other organisms. More advanced techniques now enable researchers to study nerve signals in single, intact nerve cells.

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**_Reflex Actions_** **_and the Spinal Cord_** **_Reflex Arcs_** (see Fig. 14.17).

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Central nervous system

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* outside the central nervous system * contains the nerves. 1. cranial nerves: brain and are termed 2. spinal nerves: spinal cord. 3. all nerves carry signals to and from the CNS. * So right now, your eyes are sending messages by way of a cranial nerve to the brain, allowing you to read this text. * When you’re finished, your brain will direct the muscles in your fingers, by way of the spinal cord and a spinal nerve, to proceed to the next chapter. *

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* Once a neurotransmitter has been released into a synaptic cleft and has initiated a response, it is removed from the cleft. * In some synapses, the receiving membrane contains enzymes that rapidly inactivate the neurotransmitter. * For example, the enzyme acetylcholinesterase (AChE) breaks down the neurotransmitter acetylcholine. * In other synapses, the sending membrane rapidly reabsorbs the neurotransmitter, possibly for repackaging in synaptic vesicles or for molecular breakdown. * The short existence of neurotransmitters at a synapse prevents continuous stimulation (or inhibition) of receiving membranes. * The receiving cell needs to be able to respond quickly to changing conditions. * If the neurotransmitter were to linger in the cleft, the receiving cell would be unable to respond to a new signal from a sending cell. * Neural Transmission: Synapse *

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What does the CNS do?

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14.1 Overview of the nervous system and its primary Functions

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Overview of human brain

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14.2 The Central Nervous System LEARNING OUTCOMES Upon completion of this section, you should be able to Identify the structures of the spinal cord and provide a function for each. Identify the structures of the brain and provide a function for each. Identify the lobes and major areas of the human brain. Distinguish between the functions of the primary motor and the primary somatosensory areas of the brain. The spinal cord and the brain make up the CNS, where sensory information is received and motor control is initiated. Both the spinal cord and the brain are protected by bone. The spinal cord is surrounded by vertebrae, and the brain is enclosed by the skull. Also, both the spinal cord and the brain are wrapped in protective Page 287membranes known as meninges (sing., meninx). Meningitis is an infection of the meninges and may be caused by either bacterial or viral pathogens. The spaces between the meninges are filled with cerebrospinal fluid, which cushions and protects the CNS. In a spinal tap (lumbar puncture), a small amount of this fluid is withdrawn from around the spinal cord for laboratory testing. Cerebrospinal fluid is also contained within the ventricles of the brain and in the central canal of the spinal cord. The brain has four ventricles, interconnecting chambers that produce and serve as a reservoir for cerebrospinal fluid (Fig. 14.7). Normally, any excess cerebrospinal fluid drains away into the cardiovascular system. However, blockages can occur. In an infant, the brain can enlarge due to cerebrospinal fluid accumulation, resulting in a condition called hydrocephalus (“water on the brain”). If cerebrospinal fluid collects in an adult, the brain cannot enlarge. Instead, it is pushed against the skull. Such situations cause severe brain damage and can be fatal unless quickly corrected. Figure 14.7 The ventricles of the brain. The brain has four ventricles. A lateral ventricle is found on each side of the brain. They join at the third ventricle. The third ventricle connects with the fourth ventricle superiorly; the central canal of the spinal cord joins the fourth ventricle inferiorly. All structures are filled with cerebrospinal fluid. a. Lateral view of ventricles seen through a transparent brain. b. Anterior view of ventricles seen through a transparent brain. The CNS is composed of two types of nervous tissue—gray matter and white matter. Gray matter contains cell bodies and short, nonmyelinated axons. White matter contains myelinated axons that run together in bundles called tracts. The Spinal Cord The spinal cord extends from the base of the brain through a large opening in the skull called the foramen magnum (see Fig. 12.4). From the foramen magnum, the spinal cord proceeds inferiorly in the vertebral canal. Structure of the Spinal Cord A cross-section of the spinal cord (Fig. 14.8a) shows a central canal, gray matter, and white matter. Figure 14.8b shows how an individual vertebra protects the spinal cord. The spinal nerves project from the cord through small openings called intervertebral foramina. Fibrocartilage intervertebral discs separate the vertebrae. If a disc ruptures or herniates, it may compress a spinal nerve, resulting in pain and a loss of mobility. Figure 14.8 The organization of white and gray matter in the spinal cord and the spinal nerves. a. Cross-section of the spinal cord, showing arrangements of white and gray matter. b. Spinal nerves originating from the spinal cord. c. The spinal cord is protected by vertebrae. d. Spinal nerves emerging from the cord. (a): ©Scientifica/Corbis Documentary/Getty Images; (d): ©McGraw-Hill Education/Rebecca Gray, photographer & Don Kincaid, dissections The central canal of the spinal cord contains cerebrospinal fluid, as do the meninges that protect the spinal cord. The gray matter is centrally located and shaped like the letter H (Fig. 14.8a–c). Portions of sensory neurons and motor neurons are found in gray matter, as are interneurons that communicate with these two types of neurons. The dorsal root of a spinal nerve contains sensory fibers entering the gray matter. The ventral root of a spinal nerve contains motor fibers exiting the gray matter. The dorsal and ventral roots join before the spinal nerve leaves the vertebral canal (Fig. 14.8c, d), forming a mixed nerve. Spinal nerves are a part of the PNS. The white matter of the spinal cord occurs in areas around the gray matter. The white matter contains ascending tracts taking information to the brain (primarily located posteriorly) and descending tracts taking information from the brain (primarily located anteriorly). Many tracts cross just after they enter and exit the brain, so the left side of the brain controls the right side of the body. Likewise, the right side of the brain controls the left side of the body. Functions of the Spinal Cord The spinal cord provides a means of communication between the brain and the peripheral nerves that leave the cord. When someone touches your hand, sensory receptors generate nerve signals that pass through sensory fibers to the spinal cord and up ascending tracts to the brain (see Fig. 14.2b, red arrows). The gate control theory of pain proposes that the tracts in the spinal cord have “gates” and that these gates control the flow of pain messages from the peripheral nerves to the brain. Depending on how the gates process a pain signal, the pain message can be allowed to pass directly to the brain or can be prevented from reaching the brain. Pain messages may also be blocked by other inputs, such as those received from touch receptors or endorphins. The brain coordinates the voluntary control of our limbs. Motor signals originating in the brain pass down descending tracts to the spinal cord and out to our muscles by way of motor fibers (see Fig. 14.2b, black arrows). Therefore, if the spinal cord is severed, we suffer a loss of sensation and a loss of voluntary control—paralysis. If the cut occurs in the thoracic region, the lower body and legs are paralyzed, a condition known as paraplegia. If the injury is in the neck region, all four limbs are usually affected, a condition called quadriplegia. Page 288 Reflex Actions The spinal cord is the center for thousands of reflex arcs (see Fig. 14.17). A stimulus causes sensory receptors to generate signals that travel in sensory axons to the spinal cord. Interneurons integrate the incoming data and relay signals to motor neurons. A response to the stimulus occurs when motor axons cause skeletal muscles to contract. Motor neurons in a reflex arc may also affect smooth muscle, organs, or glands. Each interneuron in the spinal cord synapses with numerous other neurons. From there, interneurons send signals to other interneurons and motor neurons. Similarly, the spinal cord creates reflex arcs for the internal organs. For example, when blood pressure falls, internal receptors in the carotid arteries and aorta generate nerve signals that pass through sensory fibers to the cord and then up an ascending tract to a cardiovascular center in the brain. Thereafter, nerve signals pass down a descending tract to the spinal cord. Motor signals then cause blood vessels to constrict, so that the blood pressure rises. The Brain The human brain has been called the last great frontier of biology. The goal of modern neuroscience is to understand the structure and function of the brain’s various parts so well that it will be possible to prevent or correct the thousands of mental disorders that rob humans of a normal life. This section gives only a glimpse of what is known about the brain and the modern avenues of research. We discuss the parts of the brain with reference to the cerebrum, the diencephalon, the cerebellum, and the brain stem. The brain’s four ventricles (see Fig. 14.7) are called, in turn, the two lateral ventricles, the third ventricle, and the fourth ventricle. It may be helpful for you to associate the cerebrum with the two lateral ventricles, the diencephalon with the third ventricle, and the brain stem and cerebellum with the fourth ventricle (Fig. 14.9a). Figure 14.9 The human brain. a. The cerebrum is the largest part of the brain in humans. b. Viewed from above, the cerebrum has left and right cerebral hemispheres. The hemispheres are connected by the corpus callosum. (b): ©McGraw-Hill Education; photo and dissection by Christine Eckel The Cerebrum The cerebrum is the largest portion of the brain in mammals, including humans. The cerebrum is the last center to receive sensory input and carry out integration before commanding voluntary motor responses. It communicates with and coordinates the activities of the other parts of the brain. Cerebral Hemispheres Just as the human body has two halves, so does the cerebrum. These halves are called the left and right cerebral hemispheres (Fig. 14.9b). A deep groove called the longitudinal fissure divides the left and right cerebral hemispheres. The two cerebral hemispheres communicate via the corpus callosum, an extensive bridge of nerve tracts. Page 289The characteristic appearance of the cerebrum is the result of thick folds, called gyri (sing., gyrus) separated by shallow grooves called sulci (sing., sulcus). The sulci divide each hemisphere into lobes (Fig. 14.10). The frontal lobe is the most anterior of the lobes (directly behind the forehead). The parietal lobe is posterior to the frontal lobe. The occipital lobe is posterior to the parietal lobe (at the rear of the head). The temporal lobe lies inferior to the frontal and parietal lobes (at the temple and the ear). Figure 14.10 The lobes of the cerebral hemispheres. Each cerebral hemisphere is divided into four lobes: frontal, parietal, temporal, and occipital. Centers in the frontal lobe control movement and higher reasoning, as well as the smell sensation. Somatic sensing is carried out by parietal lobe neurons, and those of the temporal lobe receive sound information. Visual information is received and processed in the occipital lobe. The Cerebral Cortex The cerebral cortex is a thin, highly convoluted outer layer of gray matter that covers the cerebral hemispheres. Recall that gray matter consists of neurons whose axons are not myelinated. The cerebral cortex contains over 1 billion cell bodies and is the region of the brain that accounts for sensation, voluntary movement, and all the thought processes we associate with consciousness. Primary Motor and Sensory Areas of the Cortex The cerebral cortex contains motor areas and sensory areas, as well as association areas. The primary motor area is in the frontal lobe just anterior to (before) the central sulcus. Voluntary commands to skeletal muscles begin in the primary motor area, and each part of the body is controlled by a certain section (Fig. 14.11a). In this illustration, notice that large areas of the cerebral cortex are devoted to controlling structures that carry out very fine, precise movements. Thus, the muscles that control facial movements—swallowing, salivation, expression—take up an especially large portion of the primary motor area. Likewise, hand movements require tremendous accuracy. Together, these two structures command nearly two-thirds of the primary motor area.Page 290 Figure 14.11 The primary motor and primary somatosensory areas of the brain. a. The primary motor area (blue) is located in the frontal lobe, adjacent to (b) the primary somatosensory area in the parietal lobe. The primary taste area is colored pink. The size of each body region shown indicates the relative amount of cortex devoted to control of that body region. SCIENCE IN YOUR LIFE Why does a stroke on the right side of the brain cause weakness or paralysis on the left side of the body? Descending motor tracts (from the primary motor area) and ascending sensory tracts (from the primary somatosensory area) cross over in the spinal cord and medulla. Motor neurons in the right cerebral hemisphere control the left side of the body and vice versa because of crossing-over. Likewise, sensation from the left half of the body travels to the right cerebral hemisphere. Destruction of brain tissue by a stroke interferes with outgoing motor signals to the opposite side of the body, as well as incoming sensory information from that side. The primary somatosensory area is just posterior to the central sulcus in the parietal lobe. Sensory information from the skin and skeletal muscles arrives here, where each part of the body is sequentially represented (Fig. 14.11b). Like the primary motor cortex, large areas of the primary sensory cortex are dedicated to those body areas with acute sensation. Once again, the face and hands require the largest proportion of the sensory cortex. Page 291Reception areas for the other primary sensations—taste, vision, hearing, and smell—are located in other areas of the cerebral cortex (see Fig. 14.10). The primary taste area in the parietal lobe (pink) accounts for taste sensations. Visual information is received by the primary visual cortex (blue) in the occipital lobe. The primary auditory area in the temporal lobe (green) accepts information from our ears. Smell sensations travel to the primary olfactory area (yellow) found on the deep surface of the frontal lobe. Association Areas Association areas are places where integration occurs and where memories are stored. Anterior to the primary motor area is a premotor area. The premotor area organizes motor functions for skilled motor activities, such as walking and talking at the same time. Next, the primary motor area sends signals to the cerebellum, which integrates them. A momentary lack of oxygen during birth can damage the motor areas of the cerebral cortex, resulting in cerebral palsy, a condition characterized by a spastic weakness of the arms and legs. The somatosensory association area, located just posterior to the primary somatosensory area, processes and analyzes sensory information from the skin and muscles. The visual association area in the occipital lobe associates new visual information with stored visual memories. It might “decide,” for example, if we have seen a face, scene, or symbol before. The auditory association area in the temporal lobe performs the same functions with regard to sounds. Processing Centers Processing centers of the cortex receive information from the other association areas and perform higher-level analytical functions. The prefrontal area, an association area in the frontal lobe, receives information from the other association areas and uses this information to reason and plan our actions. Integration in this area accounts for our most cherished human abilities. Reasoning, critical thinking, and formulating appropriate behaviors are possible because of integration carried out in the prefrontal area. The unique ability of humans to speak is partially dependent on two processing centers found only in the left cerebral cortex. Wernicke’s area is located in the posterior part of the left temporal lobe. Broca’s area is located in the left frontal lobe. Broca’s area is just anterior to the portion of the primary motor area for speech musculature (lips, tongue, larynx, and so forth) (see Fig. 14.10). Wernicke’s area helps us understand both the written and the spoken word and sends the information to Broca’s area. Broca’s area adds grammatical refinements and directs the primary motor area to stimulate the appropriate muscles for speaking and writing. Central White Matter Much of the rest of the cerebrum is composed of white matter. Myelination occurs and white matter develops as a child grows. Progressive myelination enables the brain to grow in size and complexity. For example, as neurons become myelinated within tracts designed for language development, children become more capable of speech. Descending tracts from the primary motor area communicate with lower brain centers, and ascending tracts from lower brain centers send sensory information up to the primary somatosensory area. Tracts within the cerebrum also take information among the different sensory, motor, and association areas pictured in Figure 14.10. The corpus callosum contains tracts that join the two cerebral hemispheres. Basal Nuclei Though the majority of each cerebral hemisphere is composed of tracts, there are masses of gray matter deep within the white matter. These basal nuclei integrate motor commands to ensure that the proper muscle groups are stimulated or inhibited. Integration ensures that movements are coordinated and smooth. Parkinson disease (see Section 18.5) is believed to be caused by degeneration of specific neurons in the basal nuclei. The Diencephalon The hypothalamus and thalamus are in the diencephalon, a region that encircles the third ventricle. The hypothalamus forms the floor of the third ventricle. The hypothalamus is an integrating center that helps maintain homeostasis. It regulates hunger, sleep, thirst, body temperature, and water balance. The hypothalamus controls the pituitary gland and thereby serves as a link between the nervous and endocrine systems. The thalamus consists of two masses of gray matter located in the sides and roof of the third ventricle. The thalamus is on the receiving end for all sensory input except the sense of smell. Visual, auditory, and somatosensory information arrives at the thalamus via the cranial nerves and tracts from the spinal cord. The thalamus integrates this information and sends it on to the appropriate portions of the cerebrum. The thalamus is involved in arousal of the cerebrum, and it participates in higher mental functions, such as memory and emotions. The pineal gland, which secretes the hormone melatonin, is located in the diencephalon. Presently, there is much popular interest in the role of melatonin in our daily rhythms. Some researchers believe it can help alleviate jet lag or insomnia. Scientists are also interested in the possibility that the hormone may regulate the onset of puberty. The Cerebellum The cerebellum lies under the occipital lobe of the cerebrum and is separated from the brain stem by the fourth ventricle. The cerebellum has two portions joined by a narrow median portion. Each portion is primarily composed of white matter. In a longitudinal section, the white matter has a treelike pattern called arbor vitae. Overlying the white matter is a thin layer of gray matter that forms a series of complex folds. The cerebellum receives sensory input from the eyes, ears, joints, and muscles about the present position of body parts. It also receives motor output from the cerebral cortex about where these parts should be located. After integrating this information, the cerebellum sends motor signals by way of the brain stem to the skeletal muscles. In this way, the cerebellum maintains posture and balance. It also ensures that all the muscles work together to produce smooth, coordinated, voluntary movements. The cerebellum assists in the learning of new motor skills, such as playing the piano or hitting a baseball. The Brain Stem The tracts cross in the brain stem, which contains the midbrain, the pons, and the medulla oblongata (see Fig. 14.9a). The midbrain acts as a relay station for tracts passing between the cerebrum and Page 292the spinal cord or cerebellum. It also has reflex centers for visual, auditory, and tactile responses. The pons (“bridge” in Latin) contains bundles of axons traveling between the cerebellum and the rest of the CNS. In addition, the pons functions with the medulla oblongata to regulate breathing rate. Reflex centers in the pons coordinate head movements in response to visual and auditory stimuli. The medulla oblongata contains a number of reflex centers for regulating heartbeat, breathing, and vasoconstriction (blood pressure). It also contains the reflex centers for vomiting, coughing, sneezing, hiccuping, and swallowing. The medulla oblongata lies just superior to the spinal cord, and it contains tracts that ascend or descend between the spinal cord and higher brain centers. Recall that tracts are groups of axons that travel together. Ascending tracts convey sensory information. Motor information is transmitted on descending tracts. The Reticular Formation The reticular formation is a complex network of nuclei, which are masses of gray matter, and fibers that extends the length of the brain stem (Fig. 14.12). The reticular formation is a major component of the reticular activating system (RAS). The RAS receives sensory signals and sends them to higher centers. Motor signals received by the RAS are sent to the spinal cord. Figure 14.12 The reticular formation of the brain. The reticular formation receives and sends on motor and sensory information to various parts of the CNS. One portion, the reticular activating system (RAS) (see arrows), arouses the cerebrum and, in this way, controls alertness versus sleep. The RAS arouses the cerebrum via the thalamus and causes a person to be alert. If you want to awaken the RAS, surprise it with sudden stimuli, such as an alarm clock ringing, bright lights, smelling salts, or cold water splashed on your face. The RAS can filter out unnecessary sensory stimuli, explaining why you can study with the TV on. Similarly, the RAS allows you to take a test without noticing the sounds of the people around you—unless the sounds are particularly distracting. To inactivate the RAS, remove visual or auditory stimuli, allowing yourself to become drowsy and drop off to sleep. General anesthetics function by artificially suppressing the RAS. A severe injury to the RAS can cause a person to become comatose, from which recovery may be impossible. CHECK YOUR PROGRESS 14.2 List the functions of the spinal cord. Answer Provides a means of communication between the brain and the peripheral nerves, and is the center for reflex actions. Summarize the major regions of the brain and describe the general function of each. Answer Cerebrum—largest part of the brain, integrates sensory inputs and coordinates the activities of the other parts of the brain; diencephalon—contains the hypothalamus and thalamus, maintains homeostasis, receives sensory input; cerebellum—sends out motor impulses by way of the brain stem to the skeletal muscles, produces smooth, coordinated voluntary movements; brain stem—contains the midbrain, pons, and medulla oblongata, acts as a relay station, and the medulla has reflex centers. Relate how the RAS aids in homeostasis. Answer The RAS regulates a person’s alertness, relays sensory signals to higher centers, and filters out unnecessary stimuli, which are important functions in being properly responsive to one’s environment. CONNECTING THE CONCEPTS For more information on the central nervous system, refer to the following discussions: Section 10.5 examines how the central nervous system controls breathing. Section 18.5 explores how aging and diseases such as Alzheimer disease influence the brain. Sections 23.3 and 23.4 outline how the size of the brain has changed over the course of human evolution.

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• Primary motor area – voluntary control of skeletal muscle • P

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* A cross-section of the spinal cord (Fig. 14.8a) shows a **central canal, gray matter, and white matter.** Figure 14.8b shows how an individual vertebra protects the spinal cord. * The **spinal nerves** project from the cord through small openings called **intervertebral foramina**. Fibrocartilage intervertebral discs separate the vertebrae. If a disc ruptures or herniates, it may compress a spinal nerve, resulting in pain and a loss of mobility. * Figure 14.8 The **organization of white and gray matter** in the spinal cord and the spinal nerves. a. Cross-section of the spinal cord, showing arrangements of white and gray matter. b. Spinal nerves originating from the spinal cord. c. The spinal cord is protected by vertebrae. d. Spinal nerves emerging from the cord. * (a): ©Scientifica/Corbis Documentary/Getty Images; (d): ©McGraw-Hill Education/Rebecca Gray, photographer & Don Kincaid, dissections * The **central canal** of the spinal cord contains **cerebrospinal fluid**, as do the **meninges** that protect the spinal cord. The **gray matter** is centrally located and shaped like the letter **H** (Fig. 14.8a–c). * Portions of sensory neurons and motor neurons are found in gray matter, as are interneurons that communicate with these two types of neurons. The **dorsal root** of a spinal nerve contains sensory fibers entering the gray matter. * The **ventral root** of a spinal nerve contains motor fibers exiting the gray matter. The dorsal and ventral roots join before the spinal nerve leaves the **vertebral canal (**Fig. 14.8c, d), forming a **mixed nerve.** Spinal nerves are a part of the PNS. * The **white matter** of the spinal cord occurs in areas around the **gray matter**. The white matter contains ascending tracts **taking information to the brain (primarily located posteriorly) and** descending tracts taking information from the brain (primarily located anteriorly). * Many tracts cross just after they enter and exit the brain, so the left side of the brain controls the right side of the body. Likewise, the right side of the brain controls the left side of the body.

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Spinal Cord Structures Central Canal/ Vertebral Canal Spinal nerves are a part of the PNS. (Fig. 14.8c, d),

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somatic system

Answer 162

1. four ventricles. 2. A lateral ventricle is found on each side of the brain. 3. They join at the third ventricle. 4. The third ventricle connects with the fourth ventricle superiorly; 5. the central canal of the spinal cord joins the fourth ventricle inferiorly. 6. All structures are filled with cerebrospinal fluid. 7. 8. a. Lateral view of ventricles seen through a transparent brain. b. Anterior view of ventricles seen through a transparent brain.

Answer 163

The three layers of the meringes layers 2 and 3 after Dura Mata

Answer 164

* The PNS: Autonomic division • * 2 divisions * 1. Sympathetic division: coordinates the body for the “fight or flight” response by speeding up metabolism, heart rate, and breathing while slowing down and regulating other functions * . 2. Parasympathetic division: counters the sympathetic system by bringing up a relaxed or the “rest and digest” state by slowing down metabolism, heart rate, and breathing, and returning other functions to normal. 14.4 The Peripheral Nervous System 8 The PNS: Autonomic division

Answer 165

Parasympathetic Division

Answer 166

1. Master **controlling and communicating system** of the body • 2. **Sensory input** – gathering information • 3. To **monitor changes (stimuli)** occurring inside and outside the body • 4. **Integration** • 5. To p**rocess and interpret sensory input and decide if action** is needed • 6. **Motor output** • A response to integrated stimuli 7. • The response **activates muscles or glands** 14.1 Overview of the nervous system T

Answer 167

Cranial Nerves Naming Overall Function Types Figure 14.16 Review and understand upload Figure 14.16

Answer 168

1. Cerebrum 2. Diencephalon 3. Cerebellum 4. Brainstem 14.2 The Central Nervous System 13 The CNS: Overview of the brain

Answer 169

14.5 Drug Therapy and Drug Abuse LEARNING OUTCOMES Upon completion of this section, you should be able to Explain the ways that drugs interact with the nervous system. Classify drugs as to whether they have a depressant, stimulant, or psychoactive effect on the nervous system. List the long-term effects of drug use on the body. As you are reading these words, synapses throughout your brain are organizing, integrating, and cataloging the information you take in. Neurotransmitters at these synapses control the firing of countless action potentials, thus creating a network of neural circuits. It is amazing to realize that all thoughts, feelings, and actions of a human are dependent on neurotransmitters in the CNS and PNS. By modifying or controlling synaptic transmission, a wide variety of drugs with neurological activity, both legal pharmaceuticals and illegal drugs of abuse, can alter mood, emotional state, behavior, and personality. Drug Mode of Action As mentioned in Section 14.1, there are more than 100 known neurotransmitters. The most widely studied neurotransmitters to date are acetylcholine, norepinephrine, dopamine, serotonin, and gamma-aminobutyric acid (GABA). Acetylcholine is an essential CNS neurotransmitter for memory circuits in the limbic system. Norepinephrine is important to dreaming, waking, and mood. The neurotransmitter dopamine plays a central role in the brain’s regulation of mood. Dopamine is also the basal nuclei neurotransmitter that helps organize coordinated movements. Serotonin is involved in thermoregulation, sleeping, emotions, and perception. GABA is an abundant inhibitory neurotransmitter in the CNS. Neuromodulators are naturally occurring molecules that block the release of a neurotransmitter or modify a neuron’s response to a neurotransmitter. Two well-known neuromodulators are substance P and endorphins. Substance P is a neuropeptide that is released by sensory neurons when pain is present. Endorphins block the release of substance P and serve as natural painkillers. Endorphins are produced by the brain during times of physical and/or emotional stress. They are associated with the “runner’s high” of joggers. Both pharmaceuticals and illegal drugs have several basic modes of action: They promote the action of a neurotransmitter, usually by increasing the amount of neurotransmitter at a synapse. Examples include drugs such as alprazolam (Xanax) and diazepam (Valium), which increase GABA. These medications are used for panic attacks and anxiety. Reduced levels of norepinephrine and serotonin are linked to depression. Drugs such as fluoxetine (Prozac), paroxetine (Paxil), and duloxetine (Cymbalta) allow norepinephrine and/or serotonin to accumulate at the synapse, which explains their effectiveness as antidepressants. Alzheimer disease causes a slow, progressive loss of memory (see Section 18.5). Drugs used for Alzheimer disease allow acetylcholine to accumulate at synapses in the limbic system. They interfere with or decrease the action of a neurotransmitter. For instance, antipsychotic drugs used for the treatment of schizophrenia decrease the activity of dopamine. The caffeine in coffee, chocolate, and tea keeps us awake by interfering with the effects of inhibitory neurotransmitters in the brain. They replace or mimic a neurotransmitter or neuromodulator. The opiates—namely, codeine, heroin, and morphine—bind to endorphin receptors and in this way reduce pain and produce a feeling of well-being. Ongoing research into neurophysiology and neuropharmacology (the study of nervous system function and the way drugs work in the nervous system) continues to provide evidence that mental illnesses are caused by imbalances in neurotransmitters. These studies will undoubtedly improve treatments for mental illness, as well as provide insight into the problem of drug abuse. Drug Abuse Like mental illness, drug abuse is linked to neurotransmitter levels. As mentioned previously, the neurotransmitter dopamine is essential for mood regulation. Dopamine plays a central role in the working of the brain’s built-in reward circuit. The reward circuit is a collection of neurons that, under normal circumstances, promotes healthy, pleasurable activities, such as consuming food. It’s possible to abuse behaviors such as eating, spending, or gambling Page 300because the behaviors stimulate the reward circuit and make us feel good. Drug abusers take drugs that artificially affect the reward circuit to the point that they neglect their basic physical needs in favor of continued drug use. Drug abuse is apparent when a person takes a drug at a dose level and under circumstances that increase the potential for a harmful effect. Drug abusers are apt to display a psychological and/or physical dependence on the drug. Psychological dependence is apparent when a person craves the drug, spends time seeking the drug, and takes it regularly. With physical dependence, formerly called “addiction,” the person has become tolerant to the drug. More is needed to get the same effect, and withdrawal symptoms occur when he or she stops taking the drug. This is true for not only teenagers and adults but also newborn babies of mothers who abuse and are addicted to drugs. Alcohol, drugs, and tobacco can all adversely affect the developing embryo, fetus, or newborn. Alcohol With the exception of caffeine, alcohol (ethanol) consumption is the most socially accepted form of drug use in the United States. According to a 2015 national survey, 26.9% of high school students reported drinking some alcohol (down from 37.4% in 2014), and 7% binge drank (five-plus drinks in one setting) during the 30 days preceding the survey. Among adults, 86.4% reported they had consumed alcohol during their lifetime, with 56% stating they had used alcohol in the past month. Alcohol acts as a depressant on many parts of the brain (Table 14.2) by increasing the action of GABA, an inhibitory neurotransmitter. Depending on the amount consumed, the effects of alcohol on the brain can lead to a feeling of relaxation, lowered inhibitions, impaired concentration and coordination, slurred speech, and vomiting. If the blood level of alcohol becomes too high, coma or death can occur. Table 14.2Drug Influence on the CNS Table Summary: Table lists the names of different substances in column 1. Other information related to these substances appears in columns 2 and 3. SubstanceEffectMode of Transmission AlcoholDepressantDrink NicotineStimulantSmoked or smokeless tobacco CocaineStimulantSniffed/snorted, injected, or smoked Methamphetamine/EcstasyStimulantSmoked or pill form HeroinDepressantSniffed/snorted, injected, or smoked Marijuana/K2PsychoactiveSmoked or consumed Beginning in about 2005, several manufacturers began selling alcoholic energy drinks. With names like Four Loko, JOOSE, and Sparks, these drinks combine fairly high levels of alcohol with caffeine and other ingredients. Although interactions between drugs can be complex, the stimulant effects of caffeine can counteract some of the depressant effects of alcohol, so users feel able to drink more. Because caffeine does not reduce the intoxicating effects of alcohol, many state legislatures are banning these products, and in November 2010 the U.S. Food and Drug Administration warned several manufacturers that they would no longer be allowed to mix caffeine with alcohol in their products. Nicotine Although the numbers have been decreasing since 2011 according to the CDC, in 2015, 25.3% of high school students and 7.4% of middle school students reported using a tobacco product. When tobacco is smoked or chewed, nicotine is rapidly delivered throughout the body. It causes a release of epinephrine from the adrenal glands, increasing blood sugar and causing the initial feeling of stimulation. As blood sugar falls, depression and fatigue set in, causing the user to seek more nicotine. In the CNS, nicotine stimulates neurons to release dopamine, a neurotransmitter that promotes a temporary sense of pleasure, and reinforces dependence on the drug. About 70% of people who try smoking become addicted. As mentioned in earlier chapters, smoking is strongly associated with serious diseases of the cardiovascular and respiratory systems. Once addicted, however, only 10–20% of smokers are able to quit. Most medical approaches to quitting smoking involve the administration of nicotine in safer forms, such as skin patches, gum, or a newly developed nicotine inhaler, so that withdrawal symptoms can be minimized while dependence is gradually reduced. Several antinicotine vaccines (such as NicVAX) are currently in development or in early clinical trials. These vaccines stimulate the production of antibodies that prevent nicotine from entering the brain. Cocaine and Crack Cocaine is an alkaloid derived from the shrub Erythroxylon coca. Approximately 35 million Americans have used cocaine by sniffing/snorting, injecting, or smoking. Cocaine is a powerful stimulant in the CNS that interferes with the reuptake of dopamine at synapses, increasing overall brain activity. The result is a rush of a sense of well-being that lasts from 5 to 30 minutes. However, long-term use of cocaine causes a loss of metabolic functions in the brain (Fig. 14.19). Figure 14.19 Cocaine use. Brain activity before and after the use of cocaine. (both photos): ©Science Source “Crack” is the street name given to cocaine that is processed to a free-base form for smoking. The term crack refers to the crackling sound heard when the drug is smoked. Smoking allows high doses of the drug to reach the brain rapidly, providing an intense and immediate high, or “rush.” Approximately 8 million Americans use crack. A cocaine binge is a period in which a user takes the drug at ever-higher doses. The user is hyperactive, with little desire for food or sleep, but has an increased sex drive. This is followed by a crash period, characterized by fatigue, depression, irritability, and a lack of interest in sex. In fact, men who use cocaine often become impotent. Cocaine is highly addictive; with continued use, the brain makes less dopamine to compensate for a seemingly endless supply. The user experiences withdrawal symptoms and an intense craving for cocaine. Overdosing on cocaine can cause cardiac and/or respiratory arrest.Page 301 Methamphetamine and Ecstasy Methamphetamine and ecstasy are considered club, or party, drugs. Methamphetamine (commonly called meth or crank) is a powerful CNS stimulant. Meth is often produced in makeshift home laboratories, usually starting with ephedrine or pseudoephedrine, common ingredients in many cold and asthma medicines. As a result, many states have passed laws making these medications more difficult to purchase. The number of toxic chemicals used to prepare the drug makes a former meth lab site hazardous to humans and to the environment. Over 9 million people in the United States have used methamphetamine at least once. It is available as a powder that can be snorted or as crystals (crystal meth or ice) that can be smoked. The structure of methamphetamine is similar to that of dopamine, and the most immediate effect of taking meth is a rush of euphoria, energy, alertness, and elevated mood. However, this is typically followed by a state of agitation that, in some individuals, leads to violent behavior. Chronic use can result in what is called an amphetamine psychosis, characterized by paranoia, hallucinations, irritability, and aggressive, erratic behavior. Ecstasy is the street name for MDMA (methylenedioxymethamphetamine), which is chemically similar to methamphetamine. Many users say that “X,” taken as a pill that looks like an aspirin or candy, increases their feelings of well-being and love for other people. However, it has many of the same side effects as other stimulants, plus it can interfere with temperature regulation, leading to hyperthermia, high blood pressure, and seizures. Although deaths from alcohol abuse are more common, ecstasy is identified as a cause of accidental death in young adults each year. Drugs with sedative effects, known as date rape or predatory drugs, include flunitrazepam (Rohypnol, or roofies), gamma-hydroxybutyric acid (GHB), and ketamine (special K). Ketamine is actually a drug that veterinarians sometimes use to perform surgery on animals. Any of these drugs can be given to an unsuspecting person, who may fall into a dreamlike state in which he or she is unable to move and thus is vulnerable to sexual assault. Heroin Heroin is derived from the resin or sap of the opium poppy plant, which is widely grown in a region from Turkey to Southeast Asia and in parts of Latin America. Drugs derived from opium are called opiates, or more commonly, opioids. This class also includes morphine and codeine. After heroin is injected, snorted, or smoked, a feeling of euphoria, along with relief of any pain, occurs within a few minutes. It is estimated that 4 million Americans have used heroin sometime in their lives, and over 300,000 people use heroin annually. As with other drugs of abuse, addiction is common. Heroin and opioids bind to receptors meant for the endorphins, naturally occurring neurotransmitters that kill pain and produce feelings of tranquility. With repeated use, the body’s production of endorphins decreases. Tolerance develops, so the user needs to take more of the drug just to prevent withdrawal symptoms (tremors, restlessness, cramps, vomiting), and the original euphoria is no longer felt. In the case of heroin, long-term users commonly acquire hepatitis, HIV/AIDS, and various bacterial infections due to the use of shared needles, and heavy users may experience convulsions and death by respiratory arrest. Heroin addiction can be treated with synthetic opiate compounds, such as methadone or buprenorphine and naloxone (Suboxone), that decrease withdrawal symptoms and block heroin’s effects. However, methadone itself can be addictive, and methadone-related deaths are on the rise. Marijuana and K2 Marijuana is the most commonly used illegal drug in the United States. Surveys vary, but in 2015, about 52% of young adults reported using marijuana in their lifetime, and 46% of the U.S. population had tried it at least once. It is derived from the dried flowering tops, leaves, and stems of the marijuana plant, Cannabis sativa, which contain and are covered by a resin that is rich in THC (tetrahydrocannabinol). The names cannabis and marijuana apply to either the plant or THC. Marijuana can be ingested, but usually it is smoked in a cigarette called a “joint.” Beginning with California in 1996, several states have legalized its use for medical purposes, such as in treating cancer, AIDS, and glaucoma. In 2012, Colorado became the first state to legalize recreational use. As of 2018, 8 states had joined Colorado in legalizing recreational use, and 22 additional states had authorized the use of marijuana for medicinal purposes. However, in 2005, the Supreme Court ruled that patients prescribed medical marijuana can still be prosecuted by federal agencies. Page 302Researchers have found that THC binds to a receptor for anandamide, a naturally occurring neurotransmitter that is important for short-term memory processing, and perhaps for feelings of contentment. The occasional marijuana user experiences mild euphoria, along with alterations in vision and judgment. Heavy use can cause hallucinations, anxiety, depression, paranoia, and psychotic symptoms. Research is underway to identify the effects of long-term marijuana use on the brain, as well as on the effects of secondhand marijuana smoke on the respiratory system. In recent years, awareness has been increasing about a synthetic compound called K2, or spice. Originally synthesized by an organic chemist at Clemson University, K2 is about ten times as potent as THC. The chemical is typically sprayed onto a mixture of other herbal products and smoked. However, because there is no regulation of how it is produced, the amount of K2 itself, or contaminants, can vary greatly. This may account for the several reports of serious medical problems and even deaths among K2 users. CHECK YOUR PROGRESS 14.5 Contrast drug therapy and drug abuse. Answer Drug therapy is used to treat a disease or disorder. Drug abuse is using drugs without symptoms of disease or disorder. List how the abuse of drugs, including alcohol and nicotine, affects the nervous system. Answer Alcohol and heroin are depressants; nicotine, cocaine, and methamphetamines are stimulants; marijuana produces euphoria. Detail several modes of action of pharmaceutical and illegal drugs. Answer Alcohol increases the action of GABA and increases the release of endorphins in the hypothalamus. Nicotine stimulates dopamine release. Cocaine inhibits dopamine reuptake. Methamphetamine mimics the action of cocaine. Heroin is converted to morphine in the brain and binds to opioid receptors. Marijuana stimulates anandamide receptors. CONNECTING THE CONCEPTS For more on the long-term effects of drug use on the systems of the body, refer to the following discussions: Section 5.7 explores the negative long-term effects of smoking on the cardiovascular system. Section 11.4 provides information on how alcohol acts as a diuretic in the urinary system. Section 20.2 examines the relationship between smoking and alcohol use and the increased risk of cancer. CONCLUSION The cause of multiple sclerosis (MS) is still unknown, but most researchers agree that there are most likely many contributing factors, including environmental influences, genetics, and a faulty immune system. Many individuals with MS are able to control their symptoms by using immunosuppressive medications, such as beta interferons. The fact that this treatment works suggests that, in many cases, MS is caused by the immune system incorrectly identifying the myelin sheaths as foreign material. The breakdown of the myelin can be detected using both MRI and SSEP tests (discussed in the chapter opener). However, environmental conditions are also suspected to cause MS. Studies have shown that the risk of contracting MS is influenced in part by where in the world you live, although the specific environmental factor or pollutant has not yet been identified. Genetics is also believed to play a role in some cases. But most researchers believe that a defect in a single gene is unlikely. Rather, it is more likely that a certain combination of genetic factors places an individual at a higher risk of contracting MS. Though there is no cure for MS, researchers have been very successful in developing disease-modifying drugs that reduce the symptoms and allow the individual to lead a normal life.

Answer 170

The peripheral nervous system (PNS) The PNS is divided into 2 systems. - Somatic division - Autonomic division

Answer 171

The Spinal Cord (Book) Figure 14.8b shows how an individual vertebra protects the spinal cord. The spinal nerves project from the cord through small openings called intervertebral foramina. Fibrocartilage intervertebral discs separate the vertebrae. If a disc ruptures or herniates, it may compress a spinal nerve, resulting in pain and a loss of mobility. * Figure 14.8 The organization of white and gray matter in the spinal cord and the spinal nerves. a. Cross-section of the spinal cord, showing arrangements of white and gray matter. b. Spinal nerves originating from the spinal cord. c. The spinal cord is protected by vertebrae. d. Spinal nerves emerging from the cord. * (a): ©Scientifica/Corbis Documentary/Getty Images; (d): ©McGraw-Hill Education/Rebecca Gray, photographer & Don Kincaid, dissections

Answer 172

Primary Motor and Sensory Area of the Cerebral Cortex See and download Figure 14.11, Page 290

Answer 173

* cortical areas may work with * lower centers to produce learning and memory. * **_Memory:_** * **__**the ability to hold a thought in mind or * to recall events from the past, ranging from a word we learned only yesterday to an early emotional experience that has shaped our lives. * Types of Memory 1. **prefrontal area,** active during **short-term memory** * seven-digit telephone number for a short time 2. **long term memory:** * ****memorized phone numbers; often associated w/ place or person associated with that number bc * mixture of 1. **semantic** memory (numbers, words, etc.) 2. **episodic** memory (persons, events, etc.). * stored in bits and pieces throughout the **sensory association areas of the cerebral cortex**. 1. Visual perceptions: vision association area 2. sounds: auditory association area 3. **_hippocampus_** serves as a **bridge** * ****between the **sensory association areas (**where memories are stored) and the **prefrontal area (where memories are used).** * prefrontal area communicates with the hippocampus when memories are stored and when these memories are brought to mind. * Some memories are emotionally charged, because the amygdala seems to be responsible for fear conditioning and associating danger with sensory stimuli received from various parts of the brain. 3. **Skill memory** * independent of episodic memory. * performing motor activities * first learns a skill, more areas of the **cerebral cortex** are involved than after the skill is perfected * later **automatic**. * all the *motor areas of the **_cerebrum below the level of consciousness._*** * Long-Term Memory Storage and Retrieval * * **_Learning_**: when we retain and use past memories. * *

Answer 174

prefrontal cortex

Answer 175

This is an infection that may be caused by either bacterial or viral pathogens and takes place in the protective covering of the brain.

Answer 176

Chapter Review SUMMARIZE 14.1Overview of the Nervous System The nervous system Is divided into the central nervous system (CNS) and the peripheral nervous system (PNS). Has three functions: (1) reception of input, (2) integration of data, and (3) generation of motor output. Nervous Tissue Nervous tissue contains the following two types of cells: neurons and neuroglia: Neurons transmit nerve signals using action potentials. Neuroglia nourish and support neurons. Anatomy of a Neuron A neuron is composed of dendrites, a cell body, and an axon. The axons of neurons may be clustered into nerves. There are three types of neurons: Sensory neurons take nerve signals from sensory receptors to the CNS. Interneurons occur within the CNS. Motor neurons take nerve signals from the CNS to effectors (muscles or glands). Myelin Sheath Long axons are covered by a myelin sheath, which is formed by the neuroglia cells. Gaps in the myelin sheath are called nodes of Ranvier. Multiple sclerosis (MS) occurs when the myelin sheath breaks down, causing a short-circuiting of nerve signals. Physiology of a Neuron Nerve signals move information within the nervous system. The generation of a nerve signal is based on the polarity across the membrane of the neuron. Resting potential: There is more Na+ outside the axon and more K+ inside the axon. The axon does not conduct a signal. The resting potential is maintained by active transport using the sodium–potassium pump. Action potential: On receipt of a stimulus strong enough to overcome the threshold, a change in polarity across the axonal membrane as a nerve signal occurs: When Na+ gates open, Na+ moves to the inside Page 303of the axon, and a depolarization occurs. When K+ gates open, K+ moves to the outside of the axon, and a repolarization occurs. Signal propagation: The presence of the myelin sheath speeds the movement of the nerve signal by saltatory conduction. After the action potential has passed, a refractory period occurs during which no additional action potentials may be processed. The Synapse At the end of each axon is an axon terminal, which borders the synapse between another neuron or target cell. When a neurotransmitter is released into a synaptic cleft, transmission of a nerve signal occurs. Binding of the neurotransmitter to receptors in the receiving membrane causes excitation or inhibition. Enzymes, such as acetylcholinesterase (AChE), assist in removing the neurotransmitter from the synaptic cleft. Neurotransmitters Neurotransmitters, such as acetylcholine, norepinephrine, and serotonin, are used to convey signals across the synapses. Integration is the summing of excitatory and inhibitory signals. 14.2The Central Nervous System The CNS receives and integrates sensory input and formulates motor output. The CNS consists of the spinal cord and brain. The CNS is protected by the meninges, which are filled with cerebrospinal fluid. The same fluid fills the four ventricles of the brain. In the CNS, gray matter contains cell bodies and nonmyelinated fibers. White matter contains myelinated axons organized as tracts. The Spinal Cord The spinal cord is responsible for conduction of information to and from the brain and carries out reflex actions. The Brain The cerebrum: The cerebrum has two cerebral hemispheres connected by the corpus callosum. Sensation, reasoning, learning and memory, and language and speech take place in the cerebrum. The cerebral cortex of each cerebral hemisphere has four lobes: frontal, parietal, occipital, and temporal. The primary motor area in the frontal lobe sends out motor commands to lower brain centers, which pass them on to motor neurons. The primary somatosensory area in the parietal lobe receives sensory information from lower brain centers in communication with sensory neurons. Association areas are located in all the lobes. The prefrontal area in the frontal lobe is involved in reasoning and planning of actions. Wernicke’s area and Broca’s area are two processing centers involved in speech. Basal nuclei: The basal nuclei integrate commands to the muscles to coordinate movement. Parkinson disease is associated with the degradation of neurons in this area. The diencephalon: The diencephalon contains both the hypothalamus and the thalamus. The hypothalamus controls homeostasis. The thalamus sends sensory input to the cerebrum. The cerebellum: The cerebellum coordinates skeletal muscle contractions. The brain stem: The brain stem includes the midbrain, the pons, and the medulla oblongata. The medulla oblongata and pons have centers for breathing and the heartbeat. The midbrain serves as a relay station between the cerebrum and spinal cord or cerebellum. The reticular formation is part of the reticular activating system (RAS), which transfers sensory signals to higher processing centers in the brain. 14.3The Limbic System and Higher Mental Functions The limbic system, located deep in the brain, is involved in determining emotions and higher mental functions, such as learning. The amygdala determines when a situation deserves the emotion we call “fear.” The hippocampus is particularly involved in storing and retrieving memories. A memory may be processed as either short-term memory or long-term memory. Long-term memory may be classified as either semantic memory or episodic memory. Skill memory is involved with processes such as riding a bike. 14.4The Peripheral Nervous System The PNS contains only nerves and ganglia (sing., ganglion). Cranial nerves take impulses to and from the brain. Spinal nerves take impulses to and from the spinal cord. The PNS is divided into the somatic system and the autonomic system. The Somatic System The somatic system serves the skin, skeletal muscles, and tendons. Some actions are due to reflexes, which are automatic and involuntary. Other actions are voluntary and originate in the cerebral cortex. The Autonomic System The autonomic system is further divided into the sympathetic division and the parasympathetic division. Sympathetic division: responses that occur during times of stress Parasympathetic division: responses that occur during times of relaxation Actions in these divisions are involuntary and automatic. These divisions innervate internal organs. Two neurons and one ganglion are used for each impulse.Page 304 14.5Drug Therapy and Drug Abuse Neurotransmitters, such as acetylcholine, norepinephrine, dopamine, and serotonin, play an important role in moving signals within the nervous system. Neuromodulators block the release of a neurotransmitter. Neurological drugs promote, prevent, or mimic the action of a particular neurotransmitter. Drugs, such as alcohol, nicotine, and marijuana, may have depressant, stimulant, or psychoactive effects. Dependency occurs when the body compensates for the presence of neurological drugs. ASSESS TESTING YOURSELF Choose the best answer for each question. 14.1Overview of the Nervous System Which of the following neuron parts receive(s) signals from sensory receptors of other neurons? cell body axon dendrites Both a and c are correct. The neuroglia cells that form myelin sheaths in the CNS are called oligodendrocytes. ganglionic cells. Schwann cells. astrocytes. microglia. Which of these correctly describes the distribution of ions on either side of an axon when it is not conducting a nerve signal? more sodium ions (Na+) outside and more potassium ions (K+) inside more K+ outside and more Na+ inside charged protein outside and Na+ and K+ inside Na+ and K+ outside and water only inside chloride ions (Cl−) outside and K+ and Na+ inside When the action potential begins, sodium gates open, allowing Na+ to cross the membrane. This causes the charge on the inside of the neuron to become more negative. more positive. neutral. None of these are correct. Repolarization of an axon during an action potential is produced by inward diffusion of Na+. outward diffusion of K+. inward active transport of Na+. active extrusion of K+. Transmission of the nerve signal across a synapse is accomplished by the movement of Na+ and K+. release of a neurotransmitter by a dendrite. release of a neurotransmitter by an axon. release of a neurotransmitter by a cell body. All of these are correct. 14.2The Central Nervous System Which of the following cerebral areas is not correctly matched with its function? occipital lobe—vision parietal lobe—somatosensory area temporal lobe—primary motor area frontal lobe—Broca’s motor speech area Which of the following brain regions is not correctly described? The medulla oblongata regulates heartbeat, breathing, and blood pressure. The cerebellum coordinates voluntary muscle movements. The thalamus secretes melatonin, which regulates daily body rhythms. The midbrain acts as a reflex center for visual, auditory, and tactile responses. This part of the brain forms the link between the nervous system and the endocrine system. corpus callosum reticular formation amygdala hypothalamus 14.3The Limbic System and Higher Mental Functions The regulation of the information that is to be relayed to memory is the function of the reticular formation. hippocampus. hypothalamus. cerebellum. pons. Memories are stored in the sensory association areas of the cerebral cortex. spinal cord. brain stem. hypothalamus. 14.4The Peripheral Nervous System Label this diagram. Page 305Which of the following is correct regarding the autonomic nervous system? The action of its two divisions tends to have opposite effects on its target organs. It is divided into sympathetic and parasympathetic divisions. It is involved in reflect responses. Major responsibilities are regulation of cardiac muscle, smooth muscles, organs, and glands. All of these are correct. The sympathetic division of the autonomic system does not cause the liver to release glycogen. dilation of bronchioles. the gastrointestinal tract to digest food. an increase in the heart rate. 14.5Drug Therapy and Drug Abuse This neurotransmitter plays an important role in sleeping, emotions, and perception. dopamine acetylcholine GABA seratonin Which of the following is a depressant of the CNS? cocaine methamphetamine ecstasy alcohol ENGAGE THINKING CRITICALLY Demyelinating disorders, such as multiple sclerosis (discussed in the chapter opener), are the subject of numerous research projects. Many investigations focus on the cells that create myelin: the Schwann cells of the PNS and oligodendrocytes in the CNS. Other studies focus on immune system cells that attack this myelin sheath. The goal of this research is to determine how to restore lost myelin, which might help (or possibly cure) people living with MS and other demyelinating diseases. Investigations into the role played by the sheath in nerve regeneration may offer hope to victims of spinal cord injury. Why are impulses transmitted more quickly down a myelinated axon than down an unmyelinated axon? A buildup of very-long-chain saturated fatty acids is believed to be the cause of myelin loss in adrenoleukodystrophy. This rare disease is a demyelinating disorder like MS. It is the subject of the film Lorenzo’s Oil. This real-life drama focuses on Lorenzo Odone, whose parents successfully developed a diet that helped their son. From your study of chemistry in Chapter 2, a fatty acid is a part of what type of molecule? What distinguishes a saturated fatty acid from an unsaturated fatty acid? From your study of nutrition in Chapter 9, what types of foods contain saturated fatty acids? Why would you expect the motor skills of a child to improve as myelination continued during early childhood development? Health Icon: ©Janis Christie/Digital Vision/Getty Images; Science Icon: ©Antenna/Getty Images; Bioethical Icon: ©JGI/Blend Images LLC ANSWER KEY Testing Yourself Click here for the answers to the Testing Yourself questions. Answer Testing Yourself: 1. c; 2. a; 3. a; 4. b; 5. b; 6. c; 7. c; 8. c; 9. d; 10. b; 11. a; 12. a. central canal; b. gray matter; c. white matter; d. cell body of interneuron; e. cell body of sensory neuron; 13. e; 14. c; 15. d; 16. d Thinking Critically Click here for the answers to the Thinking Critically questions. Answer Thinking Critically: 1. Myelin enables the signal to jump from node to node quickly, because the depolarization process occurs only at the node of Ranvier. 2a. Triglycerides, phospholipids. 2b. Unsaturated fatty acids (usually liquid at room temperature) are characterized by one or more double bonds between carbons, whereas saturated fatty acids (usually solid at room temperature) have all single bonds. 2c. Animal fat, butter, fatty cuts of meat. 3. Myelination enables signals to travel through axons more quickly, which helps coordinate motor skills.

Answer 177

Master controlling and communicating system of the body • Sensory input – gathering information • To monitor changes (stimuli) occurring inside and outside the body • Integration • To process and interpret sensory input and decide if action is needed • Motor output • A response to integrated stimuli • The response activates muscles or glands 14.1 Overview of the nervous system T

Answer 178

* Prefrontal Cortex * “CEO of the brain” * Where you control and plan your actions * Working memory * Organization * Modulate your mood * Conscience * Personality • Not fully developed until at least 25 years of age– maybe even later! (You can blame your bad decisions on this if you are younger than this-- ha!– or flip it around: drugs, alcohol, excessive videogaming, etc. can really have a permanent negative impact on this developing brain area even if you are of ‘legal age’…)

Answer 179

Processing Centers Speaking and the left cerebral cortex

Answer 180

Nerve Impulse 14.1 Overview of the Nervous System Slides \*\*\* vital short answer slide from lecture\*\* make sure to understand and add to study sheet

Answer 181

The CNS: Spinal Cord

Answer 182

1. • Drug abusers tend to show a **physiological and psychological** effect. • 2. Once a person is physically **dependent,** they usually need more of the drug for the same effect because their body has become _tolerant_, where they are used to the presence of the drug and work at this level to **_maintain homeostasis_**.

Answer 183

SCIENCE IN YOUR LIFE What is amnesia? Amnesia results from disruption of the memory pathways and can be temporary or permanent. In anterograde amnesia, injury to the limbic system separates long-term memories of events that occurred prior to the injury from events that occur in the here and now. An affected person might carry on a conversation about past events (memories of a long-ago birthday) but be unable to recall a breakfast menu from that morning. In retrograde amnesia, a blow to the head or similar injury abolishes all memories for a variable time before the injury. For example, a head injury occurring during a car accident may abolish all memories from hours to days prior to the accident.

Answer 184

The spinal cord and the brain make up the CNS, where sensory information is received and motor control is initiated. Both the spinal cord and the brain are protected by bone. The spinal cord is surrounded by vertebrae, and the brain is enclosed by the skull. Also, both the spinal cord and the brain are wrapped in protective Page 287membranes known as meninges (sing., meninx). Meningitis is an infection of the meninges and may be caused by either bacterial or viral pathogens. The spaces between the meninges are filled with cerebrospinal fluid, which cushions and protects the CNS. In a spinal tap (lumbar puncture), a small amount of this fluid is withdrawn from around the spinal cord for laboratory testing. Cerebrospinal fluid is also contained within the ventricles of the brain and in the central canal of the spinal cord. The brain has four ventricles, interconnecting chambers that produce and serve as a reservoir for cerebrospinal fluid (Fig. 14.7). Normally, any excess cerebrospinal fluid drains away into the cardiovascular system. However, blockages can occur. In an infant, the brain can enlarge due to cerebrospinal fluid accumulation, resulting in a condition called hydrocephalus (“water on the brain”). If cerebrospinal fluid collects in an adult, the brain cannot enlarge. Instead, it is pushed against the skull. Such situations cause severe brain damage and can be fatal unless quickly corrected.

Answer 185

Primary Motor and Sensory Areas of the Cortex The cerebral cortex contains motor areas and sensory areas, as well as association areas. The primary motor area is in the frontal lobe just anterior to (before) the central sulcus. Voluntary commands to skeletal muscles begin in the primary motor area, and each part of the body is controlled by a certain section (Fig. 14.11a). In this illustration, notice that large areas of the cerebral cortex are devoted to controlling structures that carry out very fine, precise movements. Thus, the muscles that control facial movements—swallowing, salivation, expression—take up an especially large portion of the primary motor area. Likewise, hand movements require tremendous accuracy. Together, these two structures command nearly two-thirds of the primary motor area.Page 290 Figure 14.11 The primary motor and primary somatosensory areas of the brain. a. The primary motor area (blue) is located in the frontal lobe, adjacent to (b) the primary somatosensory area in the parietal lobe. The primary taste area is colored pink. The size of each body region shown indicates the relative amount of cortex devoted to control of that body region. SCIENCE IN YOUR LIFE Why does a stroke on the right side of the brain cause weakness or paralysis on the left side of the body? Descending motor tracts (from the primary motor area) and ascending sensory tracts (from the primary somatosensory area) cross over in the spinal cord and medulla. Motor neurons in the right cerebral hemisphere control the left side of the body and vice versa because of crossing-over. Likewise, sensation from the left half of the body travels to the right cerebral hemisphere. Destruction of brain tissue by a stroke interferes with outgoing motor signals to the opposite side of the body, as well as incoming sensory information from that side. The primary somatosensory area is just posterior to the central sulcus in the parietal lobe. Sensory information from the skin and skeletal muscles arrives here, where each part of the body is sequentially represented (Fig. 14.11b). Like the primary motor cortex, large areas of the primary sensory cortex are dedicated to those body areas with acute sensation. Once again, the face and hands require the largest proportion of the sensory cortex. Page 291Reception areas for the other primary sensations—taste, vision, hearing, and smell—are located in other areas of the cerebral cortex (see Fig. 14.10). The primary taste area in the parietal lobe (pink) accounts for taste sensations. Visual information is received by the primary visual cortex (blue) in the occipital lobe. The primary auditory area in the temporal lobe (green) accepts information from our ears. Smell sensations travel to the primary olfactory area (yellow) found on the deep surface of the frontal lobe. Association Areas Association areas are places where integration occurs and where memories are stored. Anterior to the primary motor area is a premotor area. The premotor area organizes motor functions for skilled motor activities, such as walking and talking at the same time. Next, the primary motor area sends signals to the cerebellum, which integrates them. A momentary lack of oxygen during birth can damage the motor areas of the cerebral cortex, resulting in cerebral palsy, a condition characterized by a spastic weakness of the arms and legs. The somatosensory association area, located just posterior to the primary somatosensory area, processes and analyzes sensory information from the skin and muscles. The visual association area in the occipital lobe associates new visual information with stored visual memories. It might “decide,” for example, if we have seen a face, scene, or symbol before. The auditory association area in the temporal lobe performs the same functions with regard to sounds. Processing Centers Processing centers of the cortex receive information from the other association areas and perform higher-level analytical functions. The prefrontal area, an association area in the frontal lobe, receives information from the other association areas and uses this information to reason and plan our actions. Integration in this area accounts for our most cherished human abilities. Reasoning, critical thinking, and formulating appropriate behaviors are possible because of integration carried out in the prefrontal area. The unique ability of humans to speak is partially dependent on two processing centers found only in the left cerebral cortex. Wernicke’s area is located in the posterior part of the left temporal lobe. Broca’s area is located in the left frontal lobe. Broca’s area is just anterior to the portion of the primary motor area for speech musculature (lips, tongue, larynx, and so forth) (see Fig. 14.10). Wernicke’s area helps us understand both the written and the spoken word and sends the information to Broca’s area. Broca’s area adds grammatical refinements and directs the primary motor area to stimulate the appropriate muscles for speaking and writing. Central White Matter Much of the rest of the cerebrum is composed of white matter. Myelination occurs and white matter develops as a child grows. Progressive myelination enables the brain to grow in size and complexity. For example, as neurons become myelinated within tracts designed for language development, children become more capable of speech. Descending tracts from the primary motor area communicate with lower brain centers, and ascending tracts from lower brain centers send sensory information up to the primary somatosensory area. Tracts within the cerebrum also take information among the different sensory, motor, and association areas pictured in Figure 14.10. The corpus callosum contains tracts that join the two cerebral hemispheres. Basal Nuclei Though the majority of each cerebral hemisphere is composed of tracts, there are masses of gray matter deep within the white matter. These basal nuclei integrate motor commands to ensure that the proper muscle groups are stimulated or inhibited. Integration ensures that movements are coordinated and smooth. Parkinson disease (see Section 18.5) is believed to be caused by degeneration of specific neurons in the basal nuclei. The Diencephalon The hypothalamus and thalamus are in the diencephalon, a region that encircles the third ventricle. The hypothalamus forms the floor of the third ventricle. The hypothalamus is an integrating center that helps maintain homeostasis. It regulates hunger, sleep, thirst, body temperature, and water balance. The hypothalamus controls the pituitary gland and thereby serves as a link between the nervous and endocrine systems. The thalamus consists of two masses of gray matter located in the sides and roof of the third ventricle. The thalamus is on the receiving end for all sensory input except the sense of smell. Visual, auditory, and somatosensory information arrives at the thalamus via the cranial nerves and tracts from the spinal cord. The thalamus integrates this information and sends it on to the appropriate portions of the cerebrum. The thalamus is involved in arousal of the cerebrum, and it participates in higher mental functions, such as memory and emotions. The pineal gland, which secretes the hormone melatonin, is located in the diencephalon. Presently, there is much popular interest in the role of melatonin in our daily rhythms. Some researchers believe it can help alleviate jet lag or insomnia. Scientists are also interested in the possibility that the hormone may regulate the onset of puberty. The Cerebellum The cerebellum lies under the occipital lobe of the cerebrum and is separated from the brain stem by the fourth ventricle. The cerebellum has two portions joined by a narrow median portion. Each portion is primarily composed of white matter. In a longitudinal section, the white matter has a treelike pattern called arbor vitae. Overlying the white matter is a thin layer of gray matter that forms a series of complex folds. The cerebellum receives sensory input from the eyes, ears, joints, and muscles about the present position of body parts. It also receives motor output from the cerebral cortex about where these parts should be located. After integrating this information, the cerebellum sends motor signals by way of the brain stem to the skeletal muscles. In this way, the cerebellum maintains posture and balance. It also ensures that all the muscles work together to produce smooth, coordinated, voluntary movements. The cerebellum assists in the learning of new motor skills, such as playing the piano or hitting a baseball. The Brain Stem The tracts cross in the brain stem, which contains the midbrain, the pons, and the medulla oblongata (see Fig. 14.9a). The midbrain acts as a relay station for tracts passing between the cerebrum and Page 292the spinal cord or cerebellum. It also has reflex centers for visual, auditory, and tactile responses. The pons (“bridge” in Latin) contains bundles of axons traveling between the cerebellum and the rest of the CNS. In addition, the pons functions with the medulla oblongata to regulate breathing rate. Reflex centers in the pons coordinate head movements in response to visual and auditory stimuli. The medulla oblongata contains a number of reflex centers for regulating heartbeat, breathing, and vasoconstriction (blood pressure). It also contains the reflex centers for vomiting, coughing, sneezing, hiccuping, and swallowing. The medulla oblongata lies just superior to the spinal cord, and it contains tracts that ascend or descend between the spinal cord and higher brain centers. Recall that tracts are groups of axons that travel together. Ascending tracts convey sensory information. Motor information is transmitted on descending tracts. The Reticular Formation The reticular formation is a complex network of nuclei, which are masses of gray matter, and fibers that extends the length of the brain stem (Fig. 14.12). The reticular formation is a major component of the reticular activating system (RAS). The RAS receives sensory signals and sends them to higher centers. Motor signals received by the RAS are sent to the spinal cord. Figure 14.12 The reticular formation of the brain. The reticular formation receives and sends on motor and sensory information to various parts of the CNS. One portion, the reticular activating system (RAS) (see arrows), arouses the cerebrum and, in this way, controls alertness versus sleep. The RAS arouses the cerebrum via the thalamus and causes a person to be alert. If you want to awaken the RAS, surprise it with sudden stimuli, such as an alarm clock ringing, bright lights, smelling salts, or cold water splashed on your face. The RAS can filter out unnecessary sensory stimuli, explaining why you can study with the TV on. Similarly, the RAS allows you to take a test without noticing the sounds of the people around you—unless the sounds are particularly distracting. To inactivate the RAS, remove visual or auditory stimuli, allowing yourself to become drowsy and drop off to sleep. General anesthetics function by artificially suppressing the RAS. A severe injury to the RAS can cause a person to become comatose, from which recovery may be impossible. CHECK YOUR PROGRESS 14.2 List the functions of the spinal cord. Answer Provides a means of communication between the brain and the peripheral nerves, and is the center for reflex actions. Summarize the major regions of the brain and describe the general function of each. Answer Cerebrum—largest part of the brain, integrates sensory inputs and coordinates the activities of the other parts of the brain; diencephalon—contains the hypothalamus and thalamus, maintains homeostasis, receives sensory input; cerebellum—sends out motor impulses by way of the brain stem to the skeletal muscles, produces smooth, coordinated voluntary movements; brain stem—contains the midbrain, pons, and medulla oblongata, acts as a relay station, and the medulla has reflex centers. Relate how the RAS aids in homeostasis. Answer The RAS regulates a person’s alertness, relays sensory signals to higher centers, and filters out unnecessary stimuli, which are important functions in being properly responsive to one’s environment. CONNECTING THE CONCEPTS For more information on the central nervous system, refer to the following discussions: Section 10.5 examines how the central nervous system controls breathing. Section 18.5 explores how aging and diseases such as Alzheimer disease influence the brain. Sections 23.3 and 23.4 outline how the size of the brain has changed over the course of human evolution.

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(b): ©McGraw-Hill Education; photo and dissection by Christine Eckel The Cerebrum 1. largest portion of the brain in mammals, including humans. 2. last center to **receive s**ensory input and ***carry out integration*** before **_commanding voluntary motor responses._** 3. It c*ommunicates with and coordinates* the activities of the other parts of the brain.

Answer 187

Brain Ventricles

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1. Function: 2. Support and brace neurons (microfilaments) –Processes form barrier between capillaries and neurons, block out harmful substances in blood – 3. Guide migration of young neurons 4. Aids in synapse formation for learning and memory

Answer 189

List the functions of the spinal cord.

Answer 190

Spinal Nerves (see Fig. 14.8).

Answer 191

CHECK YOUR PROGRESS 14.1 Describe the three types of neurons, and list the three main parts of a neuron. Answer Sensory neurons take nerve signals from a sensory receptor to the CNS. Interneurons lie entirely within the CNS and communicate with other neurons. Motor neurons move nerve impulses away from the CNS to an effector. The parts are cell body, dendrites, and axon. Describe how a nerve impulse is propagated. Answer An exchange of Na+ and K+ ions generates an action potential that moves along the length of an axon. An action potential in one location stimulates the production of an action potential in an adjacent part of the axon membrane. If the nerve is myelinated, the action potential moves more quickly, “jumping” from one node of Ranvier to the next. Summarize how a nerve impulse is transmitted from one neuron to the next. Answer An action potential arrives at the axon terminal and calcium enters the terminal. Synaptic vesicles enclosing the neurotransmitter fuse with the sending neuron’s membrane. Neurotransmitters are released, travel across the synapse, and bind to receptors on the receiving neuron membrane. Sodium diffuses into the receiving neuron, and an action potential is created. CONNECTING THE CONCEPTS For more information on neurons and the nervous system, refer to the following discussions: Section 4.4 explores how stem cells may be used to regenerate nervous tissue. Figure 13.7 illustrates the role of the synapse in the neuromuscular junction. Section 15.1 explains how the peripheral nervous system sends information to and from the central nervous system.

Answer 192

## Footnote Association Areas

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The central nervous system • The CNS consists of the brain and spinal cord. • Both are protected by • Scalp and skin • Bones – skull and vertebral column • Meninges – 3 protective membranes that wrap around CNS • Cerebral spinal fluid (CSF) – space between meninges is filled with this fluid that cushions and protects the CNS • Blood brain barrier (BBB) Meninges • Dura mater • Double-layered external covering • Periosteum – dense connective tissue attached to surface of the skull • Meningeal layer – outer covering of the brain • Folds inward in several areas Meninges • Arachnoid mater • Middle layer • Web-like • Pia mater • Internal layer • Clings to the surface of the brain • Many blood vessels http://droualb.faculty.mjc.edu/Lecture%20Notes/Unit%205/Meninges\_peeled\_away

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Primary somatosensory area – for sensory information from skeletal muscle and skin •

Answer 195

Function: –Support and brace neurons (microfilaments) –Processes form barrier between capillaries and neurons, block out harmful substances in blood –Guide migration of young neurons –Aids in synapse formation for learning and memory

Answer 196

The Brain The human brain has been called the last great frontier of biology. The goal of modern neuroscience is to understand the structure and function of the brain’s various parts so well that it will be possible to prevent or correct the thousands of mental disorders that rob humans of a normal life. This section gives only a glimpse of what is known about the brain and the modern avenues of research. We discuss the parts of the brain with reference to the cerebrum, the diencephalon, the cerebellum, and the brain stem. The brain’s four ventricles (see Fig. 14.7) are called, in turn, the two lateral ventricles, the third ventricle, and the fourth ventricle. It may be helpful for you to associate the cerebrum with the two lateral ventricles, the diencephalon with the third ventricle, and the brain stem and cerebellum with the fourth ventricle (Fig. 14.9a). Figure 14.9 The human brain. a. The cerebrum is the largest part of the brain in humans. b. Viewed from above, the cerebrum has left and right cerebral hemispheres. The hemispheres are connected by the corpus callosum. (b): ©McGraw-Hill Education; photo and dissection by Christine Eckel The Cerebrum The cerebrum is the largest portion of the brain in mammals, including humans. The cerebrum is the last center to receive sensory input and carry out integration before commanding voluntary motor responses. It communicates with and coordinates the activities of the other parts of the brain. Cerebral Hemispheres Just as the human body has two halves, so does the cerebrum. These halves are called the left and right cerebral hemispheres (Fig. 14.9b). A deep groove called the longitudinal fissure divides the left and right cerebral hemispheres. The two cerebral hemispheres communicate via the corpus callosum, an extensive bridge of nerve tracts. Page 289The characteristic appearance of the cerebrum is the result of thick folds, called gyri (sing., gyrus) separated by shallow grooves called sulci (sing., sulcus). The sulci divide each hemisphere into lobes (Fig. 14.10). The frontal lobe is the most anterior of the lobes (directly behind the forehead). The parietal lobe is posterior to the frontal lobe. The occipital lobe is posterior to the parietal lobe (at the rear of the head). The temporal lobe lies inferior to the frontal and parietal lobes (at the temple and the ear). Figure 14.10 The lobes of the cerebral hemispheres. Each cerebral hemisphere is divided into four lobes: frontal, parietal, temporal, and occipital. Centers in the frontal lobe control movement and higher reasoning, as well as the smell sensation. Somatic sensing is carried out by parietal lobe neurons, and those of the temporal lobe receive sound information. Visual information is received and processed in the occipital lobe. The Cerebral Cortex The cerebral cortex is a thin, highly convoluted outer layer of gray matter that covers the cerebral hemispheres. Recall that gray matter consists of neurons whose axons are not myelinated. The cerebral cortex contains over 1 billion cell bodies and is the region of the brain that accounts for sensation, voluntary movement, and all the thought processes we associate with consciousness.

Answer 197

Alcohol With the exception of caffeine, alcohol (ethanol) consumption is the most socially accepted form of drug use in the United States. According to a 2015 national survey, 26.9% of high school students reported drinking some alcohol (down from 37.4% in 2014), and 7% binge drank (five-plus drinks in one setting) during the 30 days preceding the survey. Among adults, 86.4% reported they had consumed alcohol during their lifetime, with 56% stating they had used alcohol in the past month. Alcohol acts as a depressant on many parts of the brain (Table 14.2) by increasing the action of GABA, an inhibitory neurotransmitter. Depending on the amount consumed, the effects of alcohol on the brain can lead to a feeling of relaxation, lowered inhibitions, impaired concentration and coordination, slurred speech, and vomiting. If the blood level of alcohol becomes too high, coma or death can occur.

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1. infant, the brain enlarges due to *cerebrospinal fluid accumulation,* resulting in a condition called **hydrocephalus** (“water on the brain”). 2. If cerebrospinal fluid collects in an adult, the brain cannot enlarge. Instead, it is pushed against the skull. Such situations cause severe brain damage and can be fatal unless quickly corrected.

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* (Ch. 4 review) * Cell body – main cell where nucleus and most organelles reside * Dendrites – many short extensions that carry impulses to a cell body * Axon (nerve fiber) – single, long extension that carries impulses away from the cell body

Answer 200

What is The Reticular Formation (Fig. 14.12)- See, download and study Figure 14.12 The reticular formation of the brain. The reticular formation receives and sends on motor and sensory information to various parts of the CNS. One portion, the reticular activating system (RAS) (see arrows), arouses the cerebrum and, in this way, controls alertness versus sleep.

Answer 201

Limbic System

Answer 202

Limbic System 14.3

Answer 203

1. **cerebrospinal fluid,** 2. which **cushions and protects** the **CNS.** 3. In a **spinal tap** (lumbar puncture), a small amount of this fluid is withdrawn from around the spinal cord for laboratory testing. 4. within the **ventricles o**f the brain and in the **central canal** of the spinal cord.

Answer 204

* under the occipital lobe of the cerebrum * and is separated from the brain stem by the fourth ventricle. * The cerebellum has **_two portions j_**oined by a narrow median portion. * white matter. * treelike pattern called **_arbor vitae._** Overlying the white matter is a thin layer of **_gray matter_** that forms a series of complex folds. 1. receives **sensory input** from the eyes, ears, joints, and muscles about the **present position of body parts.** 2. It also receives **motor output** from the **cerebral cortex** about where these parts **should be located.** 3. After i**_ntegrating this information:_** sends **_motor signals_** by way of the **_brain stem_** to the **_skeletal muscles._** * maintains **_posture and balance._** * ensures that all the muscles work together to **_produce smooth, coordinated, voluntary movements._** * assists in the **_learning of new motor skills,_** such as playing the piano or hitting a baseball.

Answer 205

limbic system

Answer 206

Processing centers

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Resting Potential

Answer 208

How does transmissions across a synapse occur?

Answer 209

The Synapse Every axon branches into many fine endings, each tipped by a small swelling called an axon terminal. Each terminal lies very close to either the dendrite or the cell body of another neuron. This region of close proximity is called a synapse (Fig. 14.5). At a synapse, a small gap called the synaptic cleft separates the sending neuron from the receiving neuron. The nerve signal is unable to jump the cleft. Therefore, another means is needed to pass the nerve signal from the sending neuron to the receiving neuron. Figure 14.5 Signal transmission at the synapse. Transmission across a synapse from one neuron to another occurs when a neurotransmitter is released, diffuses across a synaptic cleft, and binds to a receptor in the membrane of the receiving neuron. Tutorial: Synaptic Cleft Transmission across a synapse is carried out by molecules called neurotransmitters, stored in synaptic Page 285vesicles in the axon terminals. (See Section 3.4 for a review of vesicle function.) The events (Fig. 14.5) at a synapse are (1) nerve signals traveling along an axon to reach an axon terminal; (2) calcium ions entering the terminal and stimulating synaptic vesicles to merge with the sending membrane; and (3) neurotransmitter molecules releasing into the synaptic cleft and diffusing across the cleft to the receiving membrane; there, neurotransmitter molecules bind with specific receptor proteins. Depending on the types of receptors, the response of the receiving neuron can be toward excitation or toward inhibition. In Figure 14.6, excitation occurs because the neurotransmitter, such as acetylcholine (ACh), has caused the sodium gate to open. Sodium ions diffuse into the receiving neuron. Inhibition would occur if a neurotransmitter caused potassium ions to exit the receiving neuron. Figure 14.6 Integration of excitatory and inhibitory signals at the synapse. a. Inhibitory signals and excitatory signals are summed up in the dendrite and cell body of the postsynaptic neuron. Only if the combined signals cause the membrane potential to rise above threshold does an action potential occur. b. In this example, threshold was not reached. (photo): (a): ©Science Source Chemical Synapses Once a neurotransmitter has been released into a synaptic cleft and has initiated a response, it is removed from the cleft. In some synapses, the receiving membrane contains enzymes that rapidly inactivate the neurotransmitter. For example, the enzyme acetylcholinesterase (AChE) breaks down the neurotransmitter acetylcholine. In other synapses, the sending membrane rapidly reabsorbs the neurotransmitter, possibly for repackaging in synaptic vesicles or for molecular breakdown. The short existence of neurotransmitters at a synapse prevents continuous stimulation (or inhibition) of receiving membranes. The receiving cell needs to be able to respond quickly to changing conditions. If the neurotransmitter were to linger in the cleft, the receiving cell would be unable to respond to a new signal from a sending cell. Neural Transmission: Synapse

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The parasympathetic division These are a few of its nicknames This is the neurotransmitter it uses

Answer 211

The peripheral nervous system (PNS) • It includes cranial nerves (12 pairs), spinal nerves (31 pairs), and ganglia (neuronal cell bodies) outside the CNS. - Spinal nerves conduct impulses to and from the spinal cord. - Cranial nerves conduct impulses to and from the brain. • The PNS is divided into 2 systems. - Somatic division - Autonomic division 14.4 The Peripheral Nervous System 2 The peripheral nervous system Figure 14.14 The structure of a nerve. 14.4 The Peripheral Nervous System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. LM PNS single nerve fiber bundle of nerve fibers blood vessel Spinal or Cranial Nerve artery and vein spinal nerves cranial nerves © PASIEKA/Science Photo Library/Science Source 3 14.4 The Peripheral Nervous System The peripheral nervous system Know these cranial nerves! Copyright © The McGraw-Hill Companies, Inc. Permission r

Answer 212

1. communication between the brain and the **peripheral nerves** that leave the cord. * When someone touches your hand, sensory receptors generate nerve signals that pass through sensory fibers to the spinal cord and up ascending tracts to the brain (see Fig. 14.2b, red arrows). * The ***_gate control theory of pain_*** proposes that the **tracts i**n the spinal cord have “gates” and that these gates control the flow of **pain messages** from the **peripheral nerves to the brain.** Depending on how the gates process a pain signal, the pain message can be allowed to pass directly to the brain or can be prevented from reaching the brain. Pain messages may also be blocked by other inputs, such as those received from touch receptors or endorphins. 1. The **brain** coordinates the **voluntary control of our limbs**. 2. **Motor signals** originating in the brain pass down **descending tracts** to the spinal cord and out to our muscles by way of motor fibers (see Fig. 14.2b, black arrows). * Therefore, if the spinal cord is severed, we suffer a loss of sensation and a loss of voluntary control—**paralysis.** If the cut occurs in the thoracic region, the lower body and legs are paralyzed, a condition known as **paraplegia.** If the injury is in the neck region, all four limbs are usually affected, a condition called **quadriplegia.** * Page 288* 1. **Reflex Actions** * The spinal cord is the center for **thousands** of reflex arcs (see Fig. 14.17). * A stimulus causes sensory receptors to generate signals that travel in sensory axons to the spinal cord. * Interneurons integrate the incoming data and relay signals to motor neurons. * A response to the stimulus occurs when motor axons cause skeletal muscles to contract. * Motor neurons in a reflex arc may also affect smooth muscle, organs, or glands. Each interneuron in the spinal cord synapses with numerous other neurons. From there, interneurons send signals to other interneurons and motor neurons. * Similarly, the spinal cord creates reflex arcs for the **internal organs**. For example, when **blood pressure f**alls, internal receptors in the carotid arteries and aorta generate nerve signals that pass through sensory fibers to the cord and then up an ascending tract to a cardiovascular center in the brain. Thereafter, nerve signals pass down a **descending tract** to the spinal cord. **Motor signals** then cause blood vessels to constrict, so that the blood pressure rises.

Answer 213

See and Study Figure 14.5 Figure 14.5 Signal transmission at the synapse. Transmission across a synapse from one neuron to another occurs when a neurotransmitter is released, diffuses across a synaptic cleft, and binds to a receptor in the membrane of the receiving neuron. **_Transmission across Synapse_** Figure 14.6 Page 285

Answer 214

The PNS: Autonomic division • The autonomic system regulates the activity of involuntary muscles (cardiac and smooth) and glands.

Answer 215

Sympathetic Division Most preganglionic fibers of the sympathetic division arise from the middle portion of the spinal cord. They terminate almost immediately in ganglia that lie near the cord. The sympathetic division is especially important during emergency situations when you might be required to fight or take flight. It accelerates the heartbeat and dilates the bronchi—active muscles, after all, require a ready supply of glucose and oxygen. Page 297Sympathetic neurons inhibit the digestive organs, as well as the kidneys and urinary bladder; the activities of these organs—digestion, defecation, and urination—are not immediately necessary if you’re under attack. The neurotransmitter released by the postganglionic axon is primarily norepinephrine (NE). The structure of NE is like that of epinephrine (adrenaline), an adrenal medulla hormone that usually increases heart rate and contractility.

Answer 216

* evolutionary ancient group of linked structures deep within the **cerebrum**. * It is a **_functional grouping_** rather than an anatomical one 1. blends primitive emotions w/ 2. higher mental functions into a united whole. * sexual behavior and eating seem pleasurable * unpleasant sensations or emotions (pain, frustration, hatred, despair) are translated by the limbic system into a **stress response.** * **_Structurally: 2 significant_** 1. **amygdala** * **** particular emotional overtones, creating sensation of fear. * use past knowledge fed to it by **association areas** to assess a current situation. * if necessary, trigger fight-or-flight reaction * So if you are out late at night and you turn to see someone in a ski mask following you, the amygdala may immediately cause you to start running. * The frontal cortex can override the limbic system, cause you to rethink the situation, and prevent you from acting out strong reactions 2. The **_hippocampus_** * learning and memory * information gateway: determines what information about the world is to be sent to memory and how this information is to be encoded and stored by other regions in the brain. * Most likely, the hippocampus can communicate with the frontal cortex, because we know that memories are an important part of our decision-making processes.

Answer 217

Structure Spinal Cord

Answer 218

Neurotransmitter Molecules

Answer 219

Functions of the Spinal Cord The spinal cord provides a means of communication between the brain and the peripheral nerves that leave the cord. When someone touches your hand, sensory receptors generate nerve signals that pass through sensory fibers to the spinal cord and up ascending tracts to the brain (see Fig. 14.2b, red arrows). The gate control theory of pain proposes that the tracts in the spinal cord have “gates” and that these gates control the flow of pain messages from the peripheral nerves to the brain. Depending on how the gates process a pain signal, the pain message can be allowed to pass directly to the brain or can be prevented from reaching the brain. Pain messages may also be blocked by other inputs, such as those received from touch receptors or endorphins. The brain coordinates the voluntary control of our limbs. Motor signals originating in the brain pass down descending tracts to the spinal cord and out to our muscles by way of motor fibers (see Fig. 14.2b, black arrows). Therefore, if the spinal cord is severed, we suffer a loss of sensation and a loss of voluntary control—paralysis. If the cut occurs in the thoracic region, the lower body and legs are paralyzed, a condition known as paraplegia. If the injury is in the neck region, all four limbs are usually affected, a condition called quadriplegia.

Answer 220

**_BIOLOGY TODAY Science_** **_Nerve Regeneration and Stem Cells_** (Fig. 14A)- See Figure 14A Regeneration of nerve cells. Outside the CNS, nerves regenerate because new neuroglia called Schwann cells form a pathway for axons to reach a muscle. In the CNS, comparable neuroglia called oligodendrocytes do not have this function.

Answer 221

* Both the brain and spinal cord are made up of 2 types of nervous tissue: 1. Gray matter – contains cell bodies and nonmyelinated fibers 2. White matter – contains myelinated axons

Answer 222

The central nervous system (CNS) consists of the brain and spinal cord. The brain is completely surrounded and protected by the skull. It connects directly to the spinal cord, similarly protected by the vertebral column.

Answer 223

What is the peripheral nervous system (PNS) Nerves! Figure 14.15 Figure 14.15 The structure of a nerve. The peripheral nervous system consists of the cranial nerves and the spinal nerves. A nerve is composed of bundles of axons separated from one another by connective tissue

Answer 224

What are the spinal cord and the brain?

Answer 225

* reception and processing of sensory information from both the external and the internal environments. * two major divisions. The major structures of the nervous system are shown in 1. central nervous system (CNS) consists of the brain and spinal cord. The brain is completely surrounded and protected by the skull. It connects directly to the spinal cord, similarly protected by the vertebral column. 2. The peripheral nervous system (PNS) consists of nerves. Nerves lie outside the CNS. * The division between the CNS and the PNS is arbitrary. * The two systems work together and are connected to each other (Fig. 14.2). **_Nervous System Functions (3 specific):_** 1. **_receives sensory input:_** Sensory receptors in skin and other organs respond to external and internal stimuli by **generating nerve signals** that travel by way of the **PNS to the CNS.** * ****For example, if you smell baking cookies, olfactory (smell) receptors in the nose use the PNS to transmit that information to the CNS. 2. The **CNS _performs information processing and integration,_** *summing up the input it receives from all over the body.* * reviews the information, stores the information as **memories,** and **creates the appropriate motor responses.** * The smell of those baking cookies evokes memories of their taste. 3. The CNS **generates motor output; _Nerve signals from the CNS go by way of the PNS to the muscles, glands, and organs,_** all in response to the cookies. * Signals to the salivary glands make you **salivate.** Your stomach generates the acid and enzymes needed to digest the cookies—even before you’ve had a bite. * The CNS also coordinates the movement of your arms and hands as you reach for the cookies.

Answer 226

* 2. The brain: Diencephalon • Includes the • Hypothalamus – helps maintain homeostasis (hunger, sleep, thirst, body temperature, and water balance) and controls pituitary gland • Thalamus – 2 masses of gray matter that receive all sensory input except smell; involved in memory and emotions • Pineal gland – secretes melatonin, the hormone that controls our daily rhythms

Answer 227

What is the hypothalamus?

Answer 228

**_Nerve Signals_**

Answer 229

1. a few cranial nerves (e.g., the vagus nerve), as well as fibers that arise from the sacral (bottom) portion of the spinal cord. * craniosacral portion of the autonomic system * In the parasympathetic division, the preganglionic fiber is long, and the postganglionic fiber is short because the ganglia lie near or within the organ. 2. housekeeper division, promotes all the internal responses we associate with a **_relaxed state._** 1. **__** For example, it causes the pupil of the eye to contract, 2. promotes digestion of food, and 3. slows heart rate. 4. rest-and-digest system. 5. The neurotransmitter used by the parasympathetic division is acetylcholine (ACh).

Answer 230

1. from the base of the brain through a large opening in the skull called the **foramen magnum** (see Fig. 12.4). * From the foramen magnum, the spinal cord proceeds inferiorly in the **vertebral canal.** **_Structure of the Spinal Cord (Visuals)_** 1. A cross-section of the spinal cord (Fig. 14.8a) shows a central canal, gray matter, and white matter. 1. Figure 14.8b shows how an individual vertebra protects the spinal cord. 2. The spinal nerves project from the cord through small openings called intervertebral foramina. Fibrocartilage intervertebral discs separate the vertebrae. If a disc ruptures or herniates, it may compress a spinal nerve, resulting in pain and a loss of mobility. 2. Figure 14.8 The organization of white and gray matter in the spinal cord and the spinal nerves. a. Cross-section of the spinal cord, showing arrangements of white and gray matter. b. Spinal nerves originating from the spinal cord. c. The spinal cord is protected by vertebrae. d. Spinal nerves emerging from the cord. 3. (a): ©Scientifica/Corbis Documentary/Getty Images; (d): ©McGraw-Hill Education/Rebecca Gray, photographer & Don Kincaid, dissections 4. The central canal of the spinal cord contains cerebrospinal fluid, as do the meninges that protect the spinal cord. The gray matter is centrally located and shaped like the letter H (Fig. 14.8a–c). 5. Portions of sensory neurons and motor neurons are found in gray matter, as are interneurons that communicate with these two types of neurons. The dorsal root of a spinal nerve contains sensory fibers entering the gray matter. The ventral root of a spinal nerve contains motor fibers exiting the gray matter. The dorsal and ventral roots join before the spinal nerve leaves the vertebral canal (Fig. 14.8c, d), forming a mixed nerve. Spinal nerves are a part of the PNS. 6. The white matter of the spinal cord occurs in areas around the gray matter. The white matter contains ascending tracts taking information to the brain (primarily located posteriorly) and descending tracts taking information from the brain (primarily located anteriorly). Many tracts cross just after they enter and exit the brain, so the left side of the brain controls the right side of the body. Likewise, the right side of the brain controls the left side of the body. 7.

Answer 231

Diencephalon

Answer 232

4.2 The Central Nervous System 24 4. The brain: The brainstem • Includes • Midbrain – relay station between the cerebrum and spinal cord or cerebellum; reflex center • Pons – a bridge between cerebellum and the CNS; regulates breathing rate; reflex center for head movements • Medulla oblongata – contains reflex centers for regulating breathing, heartbeat, and blood pressure

Answer 233

14.2 The Central Nervous System LEARNING OUTCOMES Upon completion of this section, you should be able to Identify the structures of the spinal cord and provide a function for each. Identify the structures of the brain and provide a function for each. Identify the lobes and major areas of the human brain. Distinguish between the functions of the primary motor and the primary somatosensory areas of the brain.

Answer 234

3 functions of the nervous system

Answer 235

Peripheral Nervous System

Answer 236

(Table 14.2) Drugs - See this table Table 14.2Drug Influence on the CNS Table Summary: Table lists the names of different substances in column 1. Other information related to these substances appears in columns 2 and 3. SubstanceEffectMode of Transmission AlcoholDepressantDrink NicotineStimulantSmoked or smokeless tobacco CocaineStimulantSniffed/snorted, injected, or smoked Methamphetamine/EcstasyStimulantSmoked or pill form HeroinDepressantSniffed/snorted, injected, or smoked Marijuana/K2PsychoactiveSmoked or consumed

Answer 237

1. The spinal cord provides a means of communication between the brain and the peripheral nerves that leave the cord. 2. When someone touches your hand, sensory receptors generate nerve signals that pass through sensory fibers to the spinal cord and up ascending tracts to the brain (see Fig. 14.2b, red arrows). The gate control theory of pain proposes that the tracts in the spinal cord have “gates” and that these gates control the flow of pain messages from the peripheral nerves to the brain. Depending on how the gates process a pain signal, the pain message can be allowed to pass directly to the brain or can be prevented from reaching the brain. Pain messages may also be blocked by other inputs, such as those received from touch receptors or endorphins. The brain coordinates the voluntary control of our limbs. Motor signals originating in the brain pass down descending tracts to the spinal cord and out to our muscles by way of motor fibers (see Fig. 14.2b, black arrows). Therefore, if the spinal cord is severed, we suffer a loss of sensation and a loss of voluntary control—paralysis. If the cut occurs in the thoracic region, the lower body and legs are paralyzed, a condition known as paraplegia. If the injury is in the neck region, all four limbs are usually affected, a condition called quadriplegia. Page 288 Reflex Actions The spinal cord is the center for thousands of reflex arcs (see Fig. 14.17). A stimulus causes sensory receptors to generate signals that travel in sensory axons to the spinal cord. Interneurons integrate the incoming data and relay signals to motor neurons. A response to the stimulus occurs when motor axons cause skeletal muscles to contract. Motor neurons in a reflex arc may also affect smooth muscle, organs, or glands. Each interneuron in the spinal cord synapses with numerous other neurons. From there, interneurons send signals to other interneurons and motor neurons. Similarly, the spinal cord creates reflex arcs for the internal organs. For example, when blood pressure falls, internal receptors in the carotid arteries and aorta generate nerve signals that pass through sensory fibers to the cord and then up an ascending tract to a cardiovascular center in the brain. Thereafter, nerve signals pass down a descending tract to the spinal cord. Motor signals then cause blood vessels to constrict, so that the blood pressure rises.

Answer 238

1. Transmission across a synapse is carried out by molecules called **neurotransmitters,** stored in synapticvesicles in the axon terminals. (See Section 3.4 for a review of vesicle function.) 2. The events (Fig. 14.5) at a synapse are: 1. nerve signals traveling along an axon to reach an axon terminal; 2. calcium ions entering the terminal and stimulating synaptic vesicles to merge with the sending membrane; 3. neurotransmitter molecules releasing into the synaptic cleft and diffusing across the cleft to the receiving membrane; 4. there, neurotransmitter molecules bind with specific receptor proteins. 5. Depending on the types of receptors, the response of the receiving neuron can be toward excitation or toward inhibition. * In Figure 14.6, **_excitation_** occurs because the neurotransmitter, such as acetylcholine (ACh), has caused the sodium gate to open. Sodium ions diffuse into the receiving neuron. * **_Inhibition_** would occur if a neurotransmitter caused potassium ions to exit the receiving neuron.

Answer 239

**_This is the primary function of the nervous system._** **_2 main components_** **_see_** Figure 14.1. and download and study; Page 281 **Figure 14.2** Organization of the nervous system. The red arrows are the pathways by which the CNS receives sensory information. The black arrows are the pathways by which the CNS communicates information with the PNS. Figure 14.1 The central nervous system. The central nervous system (CNS) consists of the brain and spinal cord. The peripheral nervous system (PNS) consists of the nerves, which lie outside the CNS.

Answer 240

These are the interconnecting chambers that produce and serve as a reservoir for cerebrospinal fluid (Fig. 14.7).

Answer 241

Expanding on neurons • 3 types of neurons • Sensory – takes impulses from sensory receptor to CNS • nterneuron – receives information in the CNS and sends it to a motor neuron • Motor – takes impulses from the CNS to an effector (i.e., gland or muscle fiber)

Answer 242

Memory on a cellular level Long Term Potentiation

Answer 243

Reflex Arc

Answer 244

Association areas – integration occurs here • Processing centers – perform higher level analytical functions including Wernicke’s and Broca’s areas, both involved in speech. Prefrontal area is also a processing center 14.2 The Central Nervous System 18 Wernicke’s and Broca’s aphasias • Aphasias are brain lesions/areas of damage • When Wernicke’s area is damaged, the individual is not able to process language and responds nonsensically (“word salad”) • When Broca’s area is damaged, the individual understands what is spoken to him/her, however is unable to have motor control for speech to verbally respond 1

Answer 245

4 Cerebrospinal Fluid (CSF) • 1. Similar to blood plasma composition, as it is formed from blood plasma • 2. Forms a watery cushion to protect the brain • 3. Circulated in subarachnoid space, ventricles, and central canal of the spinal cord

Answer 246

Central Nervous System Download photos and understand study them from 14.2 From slides 1. Stimulus causes sensory receptors to generate afferent signals in sensory axons to the spinal cord • 2. Interneurons in spinal cord integrate the information and relay the information to the efferent motor neurons 3. • Motor neuron axons cause skeletal and/or smooth muscles to contract 4. 5. 14.2 The Central Nervous System 11 6. 7. What does the spinal cord look like? 8. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. dorsal root dorsal root ventral root ventral root vertebra spinal cord white matter central canal gray matter gray matter white matter gray matter meninges ventral dorsal white matter central canal vertebra b. a. c. dorsal root ganglion spinal nerve dorsal root ganglion spinal nerve dorsal root branches dorsal root ganglion cut vertebrae d. Dorsal view of spinal cord and dorsal roots of spinal nerves. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a: © Karl E. Deckart/Phototake; d: © The McGraw-Hill Companies, Inc./Rebecca Gray, photographer and Don Kincaid, dissections Figure 14.7 The organization of white and gray matter in the spinal cord and the spinal nerves. 14.2 The Central Nervous S

Answer 247

a. A sensory neuron has a long axon covered by a myelin sheath that takes nerve impulses all the way from dendrites to the CNS. b. In the CNS, some interneurons, such as this one, have a short axon that is not covered by a myelin sheath. c. A motor neuron has a long axon covered by a myelin sheath that takes nerve impulses from the CNS to an effector.

Answer 248

Identify the lobes and major areas of the human brain.

Answer 249

Cerebral Hemispheres Just as the human body has two halves, so does the cerebrum. These halves are called the left and right cerebral hemispheres (Fig. 14.9b). A deep groove called the longitudinal fissure divides the left and right cerebral hemispheres. The two cerebral hemispheres communicate via the corpus callosum, an extensive bridge of nerve tracts. Page 289The characteristic appearance of the cerebrum is the result of thick folds, called gyri (sing., gyrus) separated by shallow grooves called sulci (sing., sulcus). The sulci divide each hemisphere into lobes (Fig. 14.10). The frontal lobe is the most anterior of the lobes (directly behind the forehead). The parietal lobe is posterior to the frontal lobe. The occipital lobe is posterior to the parietal lobe (at the rear of the head). The temporal lobe lies inferior to the frontal and parietal lobes (at the temple and the ear). Figure 14.10 The lobes of the cerebral hemispheres. Each cerebral hemisphere is divided into four lobes: frontal, parietal, temporal, and occipital. Centers in the frontal lobe control movement and higher reasoning, as well as the smell sensation. Somatic sensing is carried out by parietal lobe neurons, and those of the temporal lobe receive sound information. Visual information is received and processed in the occipital lobe.

Answer 250

The Cerebellum

Answer 251

Anatomy of a Neuron

Answer 252

Drug abuse: Marijuana • Marijuana – psychoactive drug derived from a hemp plant called Cannabis; legal medical use and legal recreational use in some states • It is most often smoked as a “joint.” • Occasional users experience mild euphoria, alterations to vision and judgment, as well as impaired motor coordination with slurred speech. • Heavy users may experience depression, anxiety, hallucinations, paranoia, and psychotic symptoms. • Long term use may lead to brain damage. • K2 (“Spice”) is a synthetic drug with higher potency than THC, the active chemical in marijuana

Answer 253

Function of Cerebellum

Answer 254

Drugs and drug abuse • Both legal pharmaceuticals and illegal drugs of abuse have certain basic modes of action that are similar. They: – promote the action of a neurotransmitter. – interfere with or decrease the action of a neurotransmitter. – replace or mimic a neurotransmitter or neuromodulator. 1

Answer 255

These are the three types of neurons, and the one that is in the nervous system alone is...

Answer 256

Processing Centers- Prefrontal Area

Answer 257

Figure 14.17 A spinal reflex arc. A stimulus (e.g., a sharp pin) causes sensory receptors in the skin to generate nerve signals that travel in sensory axons to the spinal cord. Interneurons integrate data from sensory neurons and then relay signals to motor neurons, causing contraction of a skeletal muscle and movement of the hand away from the stimulus. SCIENCE IN YOUR LIFE How does aspirin work? Aspirin is made of a chemical called acetylsalicylic acid (ASA). Damaged tissue produces large amounts of a type of fatty acid called prostaglandin. Prostaglandin acts as a signal to the peripheral nervous system that tissue damage has occurred, which the brain interprets as pain. Prostaglandins are manufactured in the cell by an enzyme called COX (cyclooxygenase). ASA reduces the capabilities of this enzyme, thus lowering the amount of prostaglandin produced and the perception of pain. The Autonomic System The autonomic system is also in the PNS (see Fig. 14.2). The autonomic system regulates the activity of cardiac and smooth muscles, organs, and glands. The system is divided into the sympathetic and parasympathetic divisions (Fig. 14.18). Activation of these two systems generally causes opposite responses. Figure 14.18 The two divisions of the autonomic nervous system. Sympathetic preganglionic fibers (left) arise from the thoracic and lumbar portions of the spinal cord; parasympathetic preganglionic fibers (right) arise from the cranial and sacral portions of the spinal cord. Each system innervates the same organs but has contrary effects. Although their functions are different, the two divisions share some features: (1) They usually function in an involuntary manner; (2) they innervate all internal organs; and (3) they use two neurons and one ganglion for each impulse. The first neuron has a cell body within the CNS and a preganglionic fiber that enters the ganglion. The second neuron has a cell body within a ganglion and a postganglionic fiber that leaves the ganglion. Reflex actions, such as those that regulate blood pressure and breathing rate, are especially important to the maintenance of homeostasis. These reflexes begin when the sensory neurons in contact with internal organs send messages to the CNS. They are completed by motor neurons within the autonomic system. Sympathetic Division Most preganglionic fibers of the sympathetic division arise from the middle portion of the spinal cord. They terminate almost immediately in ganglia that lie near the cord. The sympathetic division is especially important during emergency situations when you might be required to fight or take flight. It accelerates the heartbeat and dilates the bronchi—active muscles, after all, require a ready supply of glucose and oxygen. Page 297Sympathetic neurons inhibit the digestive organs, as well as the kidneys and urinary bladder; the activities of these organs—digestion, defecation, and urination—are not immediately necessary if you’re under attack. The neurotransmitter released by the postganglionic axon is primarily norepinephrine (NE). The structure of NE is like that of epinephrine (adrenaline), an adrenal medulla hormone that usually increases heart rate and contractility. Parasympathetic Division The parasympathetic division includes a few cranial nerves (e.g., the vagus nerve), as well as fibers that arise from the sacral (bottom) portion of the spinal cord. Therefore, this division is often referred to as the craniosacral portion of the autonomic system. In the parasympathetic division, the preganglionic fiber is long, and the postganglionic fiber is short because the ganglia lie near or within the organ. The parasympathetic division, sometimes called the housekeeper division, promotes all the internal responses we associate with a relaxed state. For example, it causes the pupil of the eye to contract, promotes digestion of food, and slows heart rate. It has been suggested that the parasympathetic system could be called the rest-and-digest system. The neurotransmitter used by the parasympathetic division is acetylcholine (ACh). The Somatic Versus the Autonomic Systems Recall that the PNS includes the somatic system and the autonomic system. Table 14.1 compares the features and functions of the somatic motor pathway with the motor pathways of the autonomic system. Table 14.1Comparison of Somatic Motor and Autonomic Motor Pathways Table Summary: Columns are for somatic motor pathway and autonomic motor pathways. Rows are for different points of comparison. Autonomic motor pathways are grouped into sympathetic and parasympathetic, as the other column-headers. Autonomic Motor Pathways Somatic Motor PathwaySympatheticParasympathetic Type of controlVoluntary/involuntaryInvoluntaryInvoluntary Number of neurons per messageOneTwo (preganglionic shorter than postganglionic)Two (preganglionic longer than postganglionic) Location of motor fiberMost cranial nerves and all spinal nervesThoracolumbar spinal nervesCranial (e.g., vagus) and sacral spinal nerves NeurotransmitterAcetylcholineNorepinephrineAcetylcholine EffectorsSkeletal musclesSmooth and cardiac muscle, glands, and organsSmooth and cardiac muscle, glands, and organs CHECK YOUR PROGRESS 14.4 Contrast cranial and spinal nerves. Answer The 12 pairs of cranial nerves receive sensory input from and send motor outputs primarily to the head region. The 31 pairs of spinal nerves receive sensory input from and send motor outputs to the rest of the body. Detail the fastest way for you to react to a stimulus. Answer A reflex action is fastest when it involves just the reflex arc that passes only through the spinal cord, not the brain. Predict what could happen to homeostasis if the autonomic nervous system failed. Answer Without the autonomic nervous system, activities of the cardiac muscles, smooth muscles, and glands would have to be regulated voluntarily. Maintaining homeostasis would be an overwhelming task. CONNECTING THE CONCEPTS For more on the interaction of the PNS with the other systems of the body, refer to the following discussions: Section 5.3 explores how the divisions of the autonomic system regulate the heart rate and help maintain homeostasis. Section 10.5 examines how signals between the brain and the diaphragm control the rate of breathing. Section 15.1 provides an overview of the types of sensory inputs processed by the peripheral nervous system.

Answer 258

Brain Stem

Answer 259

A cross-section of the spinal cord shows a 1. **central canal**, 2. **gray matter, and** 3. **white matter**

Answer 260

This type of neuron takes nerve signals from a sensory receptor to the CNS.

Answer 261

Sympathetic Division

Answer 262

Important concepts to focus on • What are the divisions of the nervous system? • What are the functions of the nervous system? • What are the three types of neurons? • What are neuroglia? • What is the structure of a neuron? • What is the myelin sheath? Saltatory conduction? Schwann cell? Node of Ranvier? • Explain the resting and action potential as they relate to a nerve impulse. • How does the nerve impulse traverse the synapse? • What are the 4 parts of the brain and their functions? • What structures protect the CNS? • What are the 2 parts of the peripheral nervous system? • Describe the actions of some drugs of abuse

Answer 263

1. branched cells that wrap CNS nerve fibers 2. Produce fatty insulating coverings (myelin sheath) around nerve fibers in the CNS – Can coil around as many as 60 different fibers at one time

Answer 264

1. Much of the rest of the cerebrum 2. Myelination occurs and white matter develops as a child grows. * **Progressive myelination** * enables the brain to grow in size and complexity. For example, as neurons become myelinated within tracts designed for **language development,** children become more capable of speech. Descending tracts from the primary motor area communicate with lower brain centers, and ascending tracts from lower brain centers send sensory information up to the primary somatosensory area. * Tracts within the cerebrum also take information among the different sensory, motor, and association areas pictured in Figure 14.10. * The **corpus callosum** contains tracts that join the two cerebral hemispheres

Answer 265

Table 14.1Comparison of Somatic Motor and Autonomic Motor Pathways Table Summary: Columns are for somatic motor pathway and autonomic motor pathways. Rows are for different points of comparison. Autonomic motor pathways are grouped into sympathetic and parasympathetic, as the other column-headers. Autonomic Motor Pathways Somatic Motor PathwaySympatheticParasympathetic Type of controlVoluntary/involuntaryInvoluntaryInvoluntary Number of neurons per messageOneTwo (preganglionic shorter than postganglionic)Two (preganglionic longer than postganglionic) Location of motor fiberMost cranial nerves and all spinal nervesThoracolumbar spinal nervesCranial (e.g., vagus) and sacral spinal nerves NeurotransmitterAcetylcholineNorepinephrineAcetylcholine EffectorsSkeletal musclesSmooth and cardiac muscle, glands, and organsSmooth and cardiac muscle, glands, and organs

Answer 266

1. Integration is the summation (adding up) of the inhibitory and excitatory signals received by a postsynaptic neuron. • This occurs because a neuron receives many signals at once.

Answer 267

BIOLOGY TODAY Science Nerve Regeneration and Stem Cells In humans, axons outside the brain and spinal cord can regenerate—but axons inside these organs cannot (Fig. 14A). After injury, axons in the human central nervous system (CNS) degenerate, resulting in permanent loss of nervous function. Interestingly, about 90% of the cells in the brain and the spinal cord are not even neurons. They are neuroglia cells. In nerves outside the brain and spinal cord, the neuroglia cells are Schwann cells that help axons regenerate. The neuroglia cells in the CNS include microglial cells, oligodendrocytes, and astrocytes, and they inhibit axon regeneration. Figure 14A Regeneration of nerve cells. Outside the CNS, nerves regenerate because new neuroglia called Schwann cells form a pathway for axons to reach a muscle. In the CNS, comparable neuroglia called oligodendrocytes do not have this function. The spinal cord contains its own stem cells. When the spinal cord is injured in experimental animals, these stem cells proliferate. But instead of becoming functional neurons, they become neuroglia cells. Researchers are trying to understand the process that triggers the stem cells to become neuroglia cells. In the future, this understanding would allow manipulation of stem cells into neurons. In early experiments with neural stem cells in the laboratory, scientists at Johns Hopkins University caused embryonic stem (ES) cells to differentiate into spinal cord motor neurons, the type of nerve cell that causes muscles to contract. The motor neurons then produced axons. When grown in the same dish with muscle cells, the motor neurons formed neuromuscular junctions and even caused muscle contractions. The cells were then transplanted into the spinal cords of rats with spinal cord injuries. Some of the transplanted cells survived for longer than a month within the spinal cord. However, no improvement in symptoms was seen and no functional neuron connections were made. In later experiments by the same research group, paralyzed rats were first treated with drugs and nerve growth factors to overcome inhibition from the central nervous system. These techniques significantly increased the success of the transplanted neurons. Amazingly, axons of transplanted neurons reached the muscles, formed neuromuscular junctions, and provided partial relief from the paralysis. Research is being done on the use of both the body’s own stem cells and laboratory-grown stem cells to repair damaged CNS neurons. Though many questions remain, the current results are promising. Questions to Consider What is the likely reason neurons cannot simply be transplanted from other areas of the body? How might this research also help patients who suffer from neurodegenerative diseases, such as Parkinson disease? Long axons tend to have a myelin sheath, but short axons do not. The gray matter of the CNS is gray because it contains no myelinated axons; the white matter of the CNS is white because it does. In the PNS, myelin gives nerve fibers their white, glistening appearance and serves as an excellent insulator. When the myelin breaks down, as happens in multiple sclerosis (MS) (see chapter opener), then it becomes more difficult for the neurons to transmit information. In effect, MS “short-circuits” the nervous system. The myelin sheath also plays an important role in nerve regeneration within the PNS. If an axon is accidentally severed, the myelin sheath remains and serves as a passageway for new fiber growth.

Answer 268

What is a motor neuron?

Answer 269

Functions of Spinal Cord

Answer 270

Cerebellum, CNS, * 14.2 The Central Nervous System 23 3. * * Slides

Answer 271

1. cerebrum. 2. left and right cerebral hemispheres 3. **_(Fig. 14.9b)._** 4. *longitudinal fissure* divides hemispheres. 5. the 2 hemispheres communicate via the **_corpus callosum_**, an extensive bridge of nerve tracts. 6. Page 289 7. The characteristic **appearance** of the cerebrum is the result of thick folds, called **gyri** (sing., gyrus) separated by shallow grooves called **sulci** (sing., sulcus). The sulci divide each hemisphere into **lobes** (Fig. 14.10). * The frontal lobe is the most anterior of the **lobes** (directly behind the forehead): movement and higher reasoning, as well as the smell sensation * The parietal lobe is posterior to the frontal lobe: Somatic sensing * The occipital lobe is posterior to the parietal lobe (at the rear of the head): Visual information is received and processed . * The temporal lobe lies inferior to the frontal and parietal lobes (at the temple and the ear): **_Figure 14.10_** Centers in the frontal lobe control is carried out by parietal lobe neurons, and those of the temporal lobe in the occipital lobe.

Answer 272

basal nuclei

Answer 273

1. .shows how an individual vertebra protects the spinal cord. 2. The spinal nerves project from the cord through small openings called intervertebral foramina. 3. Fibrocartilage intervertebral discs separate the vertebrae. If a disc ruptures or herniates, it may compress a spinal nerve, resulting in pain and a loss of mobility.

Answer 274

The Cerebellum The cerebellum lies under the occipital lobe of the cerebrum and is separated from the brain stem by the fourth ventricle. The cerebellum has two portions joined by a narrow median portion. Each portion is primarily composed of white matter. In a longitudinal section, the white matter has a treelike pattern called arbor vitae. Overlying the white matter is a thin layer of gray matter that forms a series of complex folds. The cerebellum receives sensory input from the eyes, ears, joints, and muscles about the present position of body parts. It also receives motor output from the cerebral cortex about where these parts should be located. After integrating this information, the cerebellum sends motor signals by way of the brain stem to the skeletal muscles. In this way, the cerebellum maintains posture and balance. It also ensures that all the muscles work together to produce smooth, coordinated, voluntary movements. The cerebellum assists in the learning of new motor skills, such as playing the piano or hitting a baseball.

Answer 275

Lecture notes Na + and K+ action potential generation

Answer 276

Processing Centers in the Cortex (see Fig. 14.10). - download and see

Answer 277

1. This is the junction between the sending neuron (presynaptic membrane) and the receiving neuron (postsynaptic membrane). 2. Transmission is accomplished chemically across a small gap between the two neurons **(synaptic cleft)** by a neurotransmitter * (e.g., ACh, dopamine, or serotonin). * Neurotransmitters are stored in **synaptic vesicles** in the axon terminals

Answer 278

Autonomic Motor Pathways Somatic Motor PathwaySympatheticParasympathetic Type of controlVoluntary/involuntaryInvoluntaryInvoluntary Number of neurons per messageOneTwo (preganglionic shorter than postganglionic)Two (preganglionic longer than postganglionic) Location of motor fiberMost cranial nerves and all spinal nervesThoracolumbar spinal nervesCranial (e.g., vagus) and sacral spinal nerves NeurotransmitterAcetylcholineNorepinephrineAcetylcholine EffectorsSkeletal musclesSmooth and cardiac muscle, glands, and organsSmooth and cardiac muscle, glands, and organs CHECK YOUR PROGRESS 14.4 Contrast cranial and spinal nerves. Answer The 12 pairs of cranial nerves receive sensory input from and send motor outputs primarily to the head region. The 31 pairs of spinal nerves receive sensory input from and send motor outputs to the rest of the body. Detail the fastest way for you to react to a stimulus. Answer A reflex action is fastest when it involves just the reflex arc that passes only through the spinal cord, not the brain. Predict what could happen to homeostasis if the autonomic nervous system failed. Answer Without the autonomic nervous system, activities of the cardiac muscles, smooth muscles, and glands would have to be regulated voluntarily. Maintaining homeostasis would be an overwhelming task. CONNECTING THE CONCEPTS For more on the interaction of the PNS with the other systems of the body, refer to the following discussions: Section 5.3 explores how the divisions of the autonomic system regulate the heart rate and help maintain homeostasis. Section 10.5 examines how signals between the brain and the diaphragm control the rate of breathing. Section 15.1 provides an overview of the types of sensory inputs processed by the peripheral nervous system.

Answer 279

The Somatic Versus the Autonomic Systems Recall that the PNS includes the somatic system and the autonomic system. Table 14.1 compares the features and functions of the somatic motor pathway with the motor pathways of the autonomic system. Table 14.1Comparison of Somatic Motor and Autonomic Motor Pathways Table Summary: Columns are for somatic motor pathway and autonomic motor pathways. Rows are for different points of comparison. Autonomic motor pathways are grouped into sympathetic and parasympathetic, as the other column-headers.

Answer 280

14.5 Learning Outcomes

Answer 281

14.2 The Central Nervous System LEARNING OUTCOMES Upon completion of this section, you should be able to Identify the structures of the spinal cord and provide a function for each. Identify the structures of the brain and provide a function for each. Identify the lobes and major areas of the human brain. Distinguish between the functions of the primary motor and the primary somatosensory areas of the brain. The spinal cord and the brain make up the CNS, where sensory information is received and motor control is initiated. Both the spinal cord and the brain are protected by bone. The spinal cord is surrounded by vertebrae, and the brain is enclosed by the skull. Also, both the spinal cord and the brain are wrapped in protective Page 287membranes known as meninges (sing., meninx). Meningitis is an infection of the meninges and may be caused by either bacterial or viral pathogens. The spaces between the meninges are filled with cerebrospinal fluid, which cushions and protects the CNS. In a spinal tap (lumbar puncture), a small amount of this fluid is withdrawn from around the spinal cord for laboratory testing. Cerebrospinal fluid is also contained within the ventricles of the brain and in the central canal of the spinal cord. The brain has four ventricles, interconnecting chambers that produce and serve as a reservoir for cerebrospinal fluid (Fig. 14.7). Normally, any excess cerebrospinal fluid drains away into the cardiovascular system. However, blockages can occur. In an infant, the brain can enlarge due to cerebrospinal fluid accumulation, resulting in a condition called hydrocephalus (“water on the brain”). If cerebrospinal fluid collects in an adult, the brain cannot enlarge. Instead, it is pushed against the skull. Such situations cause severe brain damage and can be fatal unless quickly corrected. Figure 14.7 The ventricles of the brain. The brain has four ventricles. A lateral ventricle is found on each side of the brain. They join at the third ventricle. The third ventricle connects with the fourth ventricle superiorly; the central canal of the spinal cord joins the fourth ventricle inferiorly. All structures are filled with cerebrospinal fluid. a. Lateral view of ventricles seen through a transparent brain. b. Anterior view of ventricles seen through a transparent brain. The CNS is composed of two types of nervous tissue—gray matter and white matter. Gray matter contains cell bodies and short, nonmyelinated axons. White matter contains myelinated axons that run together in bundles called tracts. The Spinal Cord The spinal cord extends from the base of the brain through a large opening in the skull called the foramen magnum (see Fig. 12.4). From the foramen magnum, the spinal cord proceeds inferiorly in the vertebral canal. Structure of the Spinal Cord A cross-section of the spinal cord (Fig. 14.8a) shows a central canal, gray matter, and white matter. Figure 14.8b shows how an individual vertebra protects the spinal cord. The spinal nerves project from the cord through small openings called intervertebral foramina. Fibrocartilage intervertebral discs separate the vertebrae. If a disc ruptures or herniates, it may compress a spinal nerve, resulting in pain and a loss of mobility. Figure 14.8 The organization of white and gray matter in the spinal cord and the spinal nerves. a. Cross-section of the spinal cord, showing arrangements of white and gray matter. b. Spinal nerves originating from the spinal cord. c. The spinal cord is protected by vertebrae. d. Spinal nerves emerging from the cord. (a): ©Scientifica/Corbis Documentary/Getty Images; (d): ©McGraw-Hill Education/Rebecca Gray, photographer & Don Kincaid, dissections The central canal of the spinal cord contains cerebrospinal fluid, as do the meninges that protect the spinal cord. The gray matter is centrally located and shaped like the letter H (Fig. 14.8a–c). Portions of sensory neurons and motor neurons are found in gray matter, as are interneurons that communicate with these two types of neurons. The dorsal root of a spinal nerve contains sensory fibers entering the gray matter. The ventral root of a spinal nerve contains motor fibers exiting the gray matter. The dorsal and ventral roots join before the spinal nerve leaves the vertebral canal (Fig. 14.8c, d), forming a mixed nerve. Spinal nerves are a part of the PNS. The white matter of the spinal cord occurs in areas around the gray matter. The white matter contains ascending tracts taking information to the brain (primarily located posteriorly) and descending tracts taking information from the brain (primarily located anteriorly). Many tracts cross just after they enter and exit the brain, so the left side of the brain controls the right side of the body. Likewise, the right side of the brain controls the left side of the body. Functions of the Spinal Cord The spinal cord provides a means of communication between the brain and the peripheral nerves that leave the cord. When someone touches your hand, sensory receptors generate nerve signals that pass through sensory fibers to the spinal cord and up ascending tracts to the brain (see Fig. 14.2b, red arrows). The gate control theory of pain proposes that the tracts in the spinal cord have “gates” and that these gates control the flow of pain messages from the peripheral nerves to the brain. Depending on how the gates process a pain signal, the pain message can be allowed to pass directly to the brain or can be prevented from reaching the brain. Pain messages may also be blocked by other inputs, such as those received from touch receptors or endorphins. The brain coordinates the voluntary control of our limbs. Motor signals originating in the brain pass down descending tracts to the spinal cord and out to our muscles by way of motor fibers (see Fig. 14.2b, black arrows). Therefore, if the spinal cord is severed, we suffer a loss of sensation and a loss of voluntary control—paralysis. If the cut occurs in the thoracic region, the lower body and legs are paralyzed, a condition known as paraplegia. If the injury is in the neck region, all four limbs are usually affected, a condition called quadriplegia. Page 288 Reflex Actions The spinal cord is the center for thousands of reflex arcs (see Fig. 14.17). A stimulus causes sensory receptors to generate signals that travel in sensory axons to the spinal cord. Interneurons integrate the incoming data and relay signals to motor neurons. A response to the stimulus occurs when motor axons cause skeletal muscles to contract. Motor neurons in a reflex arc may also affect smooth muscle, organs, or glands. Each interneuron in the spinal cord synapses with numerous other neurons. From there, interneurons send signals to other interneurons and motor neurons. Similarly, the spinal cord creates reflex arcs for the internal organs. For example, when blood pressure falls, internal receptors in the carotid arteries and aorta generate nerve signals that pass through sensory fibers to the cord and then up an ascending tract to a cardiovascular center in the brain. Thereafter, nerve signals pass down a descending tract to the spinal cord. Motor signals then cause blood vessels to constrict, so that the blood pressure rises. The Brain The human brain has been called the last great frontier of biology. The goal of modern neuroscience is to understand the structure and function of the brain’s various parts so well that it will be possible to prevent or correct the thousands of mental disorders that rob humans of a normal life. This section gives only a glimpse of what is known about the brain and the modern avenues of research. We discuss the parts of the brain with reference to the cerebrum, the diencephalon, the cerebellum, and the brain stem. The brain’s four ventricles (see Fig. 14.7) are called, in turn, the two lateral ventricles, the third ventricle, and the fourth ventricle. It may be helpful for you to associate the cerebrum with the two lateral ventricles, the diencephalon with the third ventricle, and the brain stem and cerebellum with the fourth ventricle (Fig. 14.9a). Figure 14.9 The human brain. a. The cerebrum is the largest part of the brain in humans. b. Viewed from above, the cerebrum has left and right cerebral hemispheres. The hemispheres are connected by the corpus callosum. (b): ©McGraw-Hill Education; photo and dissection by Christine Eckel The Cerebrum The cerebrum is the largest portion of the brain in mammals, including humans. The cerebrum is the last center to receive sensory input and carry out integration before commanding voluntary motor responses. It communicates with and coordinates the activities of the other parts of the brain. Cerebral Hemispheres Just as the human body has two halves, so does the cerebrum. These halves are called the left and right cerebral hemispheres (Fig. 14.9b). A deep groove called the longitudinal fissure divides the left and right cerebral hemispheres. The two cerebral hemispheres communicate via the corpus callosum, an extensive bridge of nerve tracts. Page 289The characteristic appearance of the cerebrum is the result of thick folds, called gyri (sing., gyrus) separated by shallow grooves called sulci (sing., sulcus). The sulci divide each hemisphere into lobes (Fig. 14.10). The frontal lobe is the most anterior of the lobes (directly behind the forehead). The parietal lobe is posterior to the frontal lobe. The occipital lobe is posterior to the parietal lobe (at the rear of the head). The temporal lobe lies inferior to the frontal and parietal lobes (at the temple and the ear). Figure 14.10 The lobes of the cerebral hemispheres. Each cerebral hemisphere is divided into four lobes: frontal, parietal, temporal, and occipital. Centers in the frontal lobe control movement and higher reasoning, as well as the smell sensation. Somatic sensing is carried out by parietal lobe neurons, and those of the temporal lobe receive sound information. Visual information is received and processed in the occipital lobe. The Cerebral Cortex The cerebral cortex is a thin, highly convoluted outer layer of gray matter that covers the cerebral hemispheres. Recall that gray matter consists of neurons whose axons are not myelinated. The cerebral cortex contains over 1 billion cell bodies and is the region of the brain that accounts for sensation, voluntary movement, and all the thought processes we associate with consciousness. Primary Motor and Sensory Areas of the Cortex The cerebral cortex contains motor areas and sensory areas, as well as association areas. The primary motor area is in the frontal lobe just anterior to (before) the central sulcus. Voluntary commands to skeletal muscles begin in the primary motor area, and each part of the body is controlled by a certain section (Fig. 14.11a). In this illustration, notice that large areas of the cerebral cortex are devoted to controlling structures that carry out very fine, precise movements. Thus, the muscles that control facial movements—swallowing, salivation, expression—take up an especially large portion of the primary motor area. Likewise, hand movements require tremendous accuracy. Together, these two structures command nearly two-thirds of the primary motor area.Page 290 Figure 14.11 The primary motor and primary somatosensory areas of the brain. a. The primary motor area (blue) is located in the frontal lobe, adjacent to (b) the primary somatosensory area in the parietal lobe. The primary taste area is colored pink. The size of each body region shown indicates the relative amount of cortex devoted to control of that body region. SCIENCE IN YOUR LIFE Why does a stroke on the right side of the brain cause weakness or paralysis on the left side of the body? Descending motor tracts (from the primary motor area) and ascending sensory tracts (from the primary somatosensory area) cross over in the spinal cord and medulla. Motor neurons in the right cerebral hemisphere control the left side of the body and vice versa because of crossing-over. Likewise, sensation from the left half of the body travels to the right cerebral hemisphere. Destruction of brain tissue by a stroke interferes with outgoing motor signals to the opposite side of the body, as well as incoming sensory information from that side. The primary somatosensory area is just posterior to the central sulcus in the parietal lobe. Sensory information from the skin and skeletal muscles arrives here, where each part of the body is sequentially represented (Fig. 14.11b). Like the primary motor cortex, large areas of the primary sensory cortex are dedicated to those body areas with acute sensation. Once again, the face and hands require the largest proportion of the sensory cortex. Page 291Reception areas for the other primary sensations—taste, vision, hearing, and smell—are located in other areas of the cerebral cortex (see Fig. 14.10). The primary taste area in the parietal lobe (pink) accounts for taste sensations. Visual information is received by the primary visual cortex (blue) in the occipital lobe. The primary auditory area in the temporal lobe (green) accepts information from our ears. Smell sensations travel to the primary olfactory area (yellow) found on the deep surface of the frontal lobe. Association Areas Association areas are places where integration occurs and where memories are stored. Anterior to the primary motor area is a premotor area. The premotor area organizes motor functions for skilled motor activities, such as walking and talking at the same time. Next, the primary motor area sends signals to the cerebellum, which integrates them. A momentary lack of oxygen during birth can damage the motor areas of the cerebral cortex, resulting in cerebral palsy, a condition characterized by a spastic weakness of the arms and legs. The somatosensory association area, located just posterior to the primary somatosensory area, processes and analyzes sensory information from the skin and muscles. The visual association area in the occipital lobe associates new visual information with stored visual memories. It might “decide,” for example, if we have seen a face, scene, or symbol before. The auditory association area in the temporal lobe performs the same functions with regard to sounds. Processing Centers Processing centers of the cortex receive information from the other association areas and perform higher-level analytical functions. The prefrontal area, an association area in the frontal lobe, receives information from the other association areas and uses this information to reason and plan our actions. Integration in this area accounts for our most cherished human abilities. Reasoning, critical thinking, and formulating appropriate behaviors are possible because of integration carried out in the prefrontal area. The unique ability of humans to speak is partially dependent on two processing centers found only in the left cerebral cortex. Wernicke’s area is located in the posterior part of the left temporal lobe. Broca’s area is located in the left frontal lobe. Broca’s area is just anterior to the portion of the primary motor area for speech musculature (lips, tongue, larynx, and so forth) (see Fig. 14.10). Wernicke’s area helps us understand both the written and the spoken word and sends the information to Broca’s area. Broca’s area adds grammatical refinements and directs the primary motor area to stimulate the appropriate muscles for speaking and writing. Central White Matter Much of the rest of the cerebrum is composed of white matter. Myelination occurs and white matter develops as a child grows. Progressive myelination enables the brain to grow in size and complexity. For example, as neurons become myelinated within tracts designed for language development, children become more capable of speech. Descending tracts from the primary motor area communicate with lower brain centers, and ascending tracts from lower brain centers send sensory information up to the primary somatosensory area. Tracts within the cerebrum also take information among the different sensory, motor, and association areas pictured in Figure 14.10. The corpus callosum contains tracts that join the two cerebral hemispheres. Basal Nuclei Though the majority of each cerebral hemisphere is composed of tracts, there are masses of gray matter deep within the white matter. These basal nuclei integrate motor commands to ensure that the proper muscle groups are stimulated or inhibited. Integration ensures that movements are coordinated and smooth. Parkinson disease (see Section 18.5) is believed to be caused by degeneration of specific neurons in the basal nuclei. The Diencephalon The hypothalamus and thalamus are in the diencephalon, a region that encircles the third ventricle. The hypothalamus forms the floor of the third ventricle. The hypothalamus is an integrating center that helps maintain homeostasis. It regulates hunger, sleep, thirst, body temperature, and water balance. The hypothalamus controls the pituitary gland and thereby serves as a link between the nervous and endocrine systems. The thalamus consists of two masses of gray matter located in the sides and roof of the third ventricle. The thalamus is on the receiving end for all sensory input except the sense of smell. Visual, auditory, and somatosensory information arrives at the thalamus via the cranial nerves and tracts from the spinal cord. The thalamus integrates this information and sends it on to the appropriate portions of the cerebrum. The thalamus is involved in arousal of the cerebrum, and it participates in higher mental functions, such as memory and emotions. The pineal gland, which secretes the hormone melatonin, is located in the diencephalon. Presently, there is much popular interest in the role of melatonin in our daily rhythms. Some researchers believe it can help alleviate jet lag or insomnia. Scientists are also interested in the possibility that the hormone may regulate the onset of puberty. The Cerebellum The cerebellum lies under the occipital lobe of the cerebrum and is separated from the brain stem by the fourth ventricle. The cerebellum has two portions joined by a narrow median portion. Each portion is primarily composed of white matter. In a longitudinal section, the white matter has a treelike pattern called arbor vitae. Overlying the white matter is a thin layer of gray matter that forms a series of complex folds. The cerebellum receives sensory input from the eyes, ears, joints, and muscles about the present position of body parts. It also receives motor output from the cerebral cortex about where these parts should be located. After integrating this information, the cerebellum sends motor signals by way of the brain stem to the skeletal muscles. In this way, the cerebellum maintains posture and balance. It also ensures that all the muscles work together to produce smooth, coordinated, voluntary movements. The cerebellum assists in the learning of new motor skills, such as playing the piano or hitting a baseball. The Brain Stem The tracts cross in the brain stem, which contains the midbrain, the pons, and the medulla oblongata (see Fig. 14.9a). The midbrain acts as a relay station for tracts passing between the cerebrum and Page 292the spinal cord or cerebellum. It also has reflex centers for visual, auditory, and tactile responses. The pons (“bridge” in Latin) contains bundles of axons traveling between the cerebellum and the rest of the CNS. In addition, the pons functions with the medulla oblongata to regulate breathing rate. Reflex centers in the pons coordinate head movements in response to visual and auditory stimuli. The medulla oblongata contains a number of reflex centers for regulating heartbeat, breathing, and vasoconstriction (blood pressure). It also contains the reflex centers for vomiting, coughing, sneezing, hiccuping, and swallowing. The medulla oblongata lies just superior to the spinal cord, and it contains tracts that ascend or descend between the spinal cord and higher brain centers. Recall that tracts are groups of axons that travel together. Ascending tracts convey sensory information. Motor information is transmitted on descending tracts. The Reticular Formation The reticular formation is a complex network of nuclei, which are masses of gray matter, and fibers that extends the length of the brain stem (Fig. 14.12). The reticular formation is a major component of the reticular activating system (RAS). The RAS receives sensory signals and sends them to higher centers. Motor signals received by the RAS are sent to the spinal cord. Figure 14.12 The reticular formation of the brain. The reticular formation receives and sends on motor and sensory information to various parts of the CNS. One portion, the reticular activating system (RAS) (see arrows), arouses the cerebrum and, in this way, controls alertness versus sleep. The RAS arouses the cerebrum via the thalamus and causes a person to be alert. If you want to awaken the RAS, surprise it with sudden stimuli, such as an alarm clock ringing, bright lights, smelling salts, or cold water splashed on your face. The RAS can filter out unnecessary sensory stimuli, explaining why you can study with the TV on. Similarly, the RAS allows you to take a test without noticing the sounds of the people around you—unless the sounds are particularly distracting. To inactivate the RAS, remove visual or auditory stimuli, allowing yourself to become drowsy and drop off to sleep. General anesthetics function by artificially suppressing the RAS. A severe injury to the RAS can cause a person to become comatose, from which recovery may be impossible. CHECK YOUR PROGRESS 14.2 List the functions of the spinal cord. Answer Provides a means of communication between the brain and the peripheral nerves, and is the center for reflex actions. Summarize the major regions of the brain and describe the general function of each. Answer Cerebrum—largest part of the brain, integrates sensory inputs and coordinates the activities of the other parts of the brain; diencephalon—contains the hypothalamus and thalamus, maintains homeostasis, receives sensory input; cerebellum—sends out motor impulses by way of the brain stem to the skeletal muscles, produces smooth, coordinated voluntary movements; brain stem—contains the midbrain, pons, and medulla oblongata, acts as a relay station, and the medulla has reflex centers. Relate how the RAS aids in homeostasis. Answer The RAS regulates a person’s alertness, relays sensory signals to higher centers, and filters out unnecessary stimuli, which are important functions in being properly responsive to one’s environment. CONNECTING THE CONCEPTS For more information on the central nervous system, refer to the following discussions: Section 10.5 examines how the central nervous system controls breathing. Section 18.5 explores how aging and diseases such as Alzheimer disease influence the brain. Sections 23.3 and 23.4 outline how the size of the brain has changed over the course of human evolution.

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Synaptic Integration A single neuron has a cell body and may have many dendrites (Fig. 14.6a). All can have synapses with many other neurons. Therefore, a neuron is on the receiving end of many signals, Page 286which can either be excitatory or inhibitory. Recall that an excitatory neurotransmitter produces an excitatory signal by opening sodium gates at a synapse. This drives the neuron closer to its threshold (illustrated by the green line in Fig. 14.6b). If threshold is reached, an action potential is inevitable. On the other hand, an inhibitory neurotransmitter drives the neuron farther from an action potential (red line in Fig. 14.6b) by opening the gates for potassium. Neurons integrate these incoming signals. Integration is the summing up of excitatory and inhibitory signals. If a neuron receives enough excitatory signals (either from different synapses or at a rapid rate from a single synapse) to outweigh the inhibitory ones, chances are the axon will transmit a signal. On the other hand, if a neuron receives more inhibitory than excitatory signals, summing these signals may prohibit the axon from reaching threshold and then depolarizing (the solid black line in Fig. 14.6b).

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**_The Synapse_** **_Axon terminal_** **_See, download study Figure 14.5_** See and Study Figure 14.5 Signal transmission at the synapse. Transmission across a synapse from one neuron to another occurs when a neurotransmitter is released, diffuses across a synaptic cleft, and binds to a receptor in the membrane of the receiving neuron. * Tutorial: Synaptic Cleft * Transmission across a synapse is carried out by molecules called neurotransmitters, stored in synaptic Page 285vesicles in the axon terminals. (See Section 3.4 for a review of vesicle function.) The events (Fig. 14.5) at a synapse are (1) nerve signals traveling along an axon to reach an axon terminal; (2) calcium ions entering the terminal and stimulating synaptic vesicles to merge with the sending membrane; and (3) neurotransmitter molecules releasing into the synaptic cleft and diffusing across the cleft to the receiving membrane; there, neurotransmitter molecules bind with specific receptor proteins. Figure 14.6 Integration of excitatory and inhibitory signals at the synapse. a. Inhibitory signals and excitatory signals are summed up in the dendrite and cell body of the postsynaptic neuron. Only if the combined signals cause the membrane potential to rise above threshold does an action potential occur. b. In this example, threshold was not reached.

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The Spinal Cord The spinal cord extends from the base of the brain through a large opening in the skull called the foramen magnum (see Fig. 12.4). From the foramen magnum, the spinal cord proceeds inferiorly in the vertebral canal.

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The Autonomic Nervous System The autonomic system is also in the PNS (see Fig. 14.2) The system is divided into the sympathetic and parasympathetic divisions (Fig. 14.18). Activation of these two systems generally causes opposite responses. Figure 14.18 The two divisions of the autonomic nervous system. Sympathetic preganglionic fibers (left) arise from the thoracic and lumbar portions of the spinal cord; parasympathetic preganglionic fibers (right) arise from the cranial and sacral portions of the spinal cord. Each system innervates the same organs but has contrary effects.

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14.2 The Central Nervous System Lecture notes Wernicke's and Broca's aphasias Which one produces word salad? (Diseases and Disorders)

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PNS: Somatic Sensory System (see Fig. 14.2). Page 296

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14.2 The Central Nervous System 24 4. The brain: The brainstem • Includes • Midbrain – relay station between the cerebrum and spinal cord or cerebellum; reflex center • Pons – a bridge between cerebellum and the CNS; regulates breathing rate; reflex center for head movements • Medulla oblongata – contains reflex centers for regulating breathing, heartbeat, and blood pressure • Reticular formation – major component of the reticular activating system (RAS) that regulates alertness (if it is damaged, you would be in a coma)

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Amygdala—fight-or-flight; hippocampus—learning and memory. The hippocampus acts as a bridge between the sensory association areas of the cerebral cortex where memories are stored long term and the prefrontal areas of the cortex where memories are used.

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1. serves the * skin, * skeletal muscles and * tendons. • 1. Automatic responses are called reflexes. • 2. Reflexes consist of * sensory receptor * sensory neuron * interneuron  * motor neuron  * effector organ (we talked about this in 14.1)

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The Reflex Arc Figure 14.17 illustrates the path of a reflex that involves only the spinal cord. If your hand touches a sharp pin, sensory receptors in the skin generate nerve signals that move along sensory fibers through the posterior (dorsal) root ganglia toward the spinal cord. Sensory neurons that enter the cord posteriorly pass signals on to many interneurons. Some of these interneurons synapse with motor neurons whose short dendrites and cell bodies are in the spinal cord. Nerve signals travel along these motor fibers to an effector, which brings about a response to the stimulus. In this case, the effector is a muscle, which contracts so that you withdraw your hand from the pin. Various other reactions are also possible—you will most likely look at the pin, wince, and cry out in pain. This whole series of responses occurs because some of the interneurons involved carry nerve signals to the brain. The brain makes you aware of the stimulus and directs these other reactions to it. In other words, you don’t feel pain until the brain receives the information and interprets it. Figure 14.17 A spinal reflex arc. A stimulus (e.g., a sharp pin) causes sensory receptors in the skin to generate nerve signals that travel in sensory axons to the spinal cord. Interneurons integrate data from sensory neurons and then relay signals to motor neurons, causing contraction of a skeletal muscle and movement of the hand away from the stimulus.

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• CNS – Astrocytes – Microglia – Ependymal cells – Oligodendrocytes • PNS – Schwann cells – Satellite cells 1

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Neurons, and their anatomy

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Science in your life? Strokes

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1. a thin, highly convoluted outer layer of _____________ that covers the cerebral hemispheres. 2. \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_consists of neurons whose axons are not\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ 3. over 1 billion cell bodies 4. *\*\*accounts for sensation, voluntary movement, and all the thought processes we associate with consciousness\*\** 5.

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Reticular Formation

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Review 14.4

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What's the Cerebral Cortex?

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* * • It joins primitive emotions (i.e., fear, pleasure) with higher functions, such as reasoning. • * It can cause strong emotional reactions to situations but conscious thought can override and direct our behavior. • * Includes • **Amygdala** – imparts emotional overtones • * **Hippocampus** – important to learning and memory

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• Reticular formation – major component of the reticular activating system (RAS) that regulates alertness (if it is damaged, you would be in a coma) 14.2 The Central Nervous System 25 The reticular formation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. RAS radiates to cerebral cortex. thalamus reticular formation ascending sensory tracts (touch, pain, temperature) Figure 14.11 The reticular formation of the brain.

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1. 18 Wernicke’s and Broca’s aphasias 1. Aphasias : brain lesions/areas of damage 2. When Wernicke’s area is damaged, the individual is not able to process language and responds nonsensically (“word salad”) • 3. When Broca’s area is damaged, the individual understands what is spoken to him/her, however is unable to have motor control for speech to verbally respond

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Structure and Location of Cerebellum

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Action Potential Propagation; This is Saltatory conduction Neural Transmission This is the name of the period during which an axon is unable to conduct an action potential, thereby ensuring :

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* Cerebrum – * ***largest portion of the brain*** • _4 lobes:_ 1. Frontal lobe: primary motor area and conscious thought 2. Temporal lobe: primary auditory, smell, and speech area 3. Parietal lobe: primary somatosensory and taste area 4. Occipital lobe: primary visual area 14. 2 The Central Nervous System 16 1. The brain: Cerebrum – The cerebral hemispheres

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4 ventricles

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This is a hormone I secrete, which is located in the diencephalon. People love me for secreting it... for insomnia and maybe even for regulating the onset of puberty.

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How the Sodium–Potassium Pump Works Action Potential The resting potential energy of the neuron can be used to perform the work of the neuron: conduction of nerve signals. The process of conduction is termed an action potential, and it occurs in the axons of neurons. A stimulus activates the neuron and begins the action potential. For example, a stimulus for pain neurons in the skin would be the prick of a sharp pin. However, the stimulus must be strong enough to cause the cell to reach threshold, the voltage that will result in an action potential. In Figure 14.4b, the threshold voltage is around −55 mV. An action potential is an all-or-nothing event. Once threshold is reached, the action potential happens automatically and completely. On the other hand, if the threshold voltage is never reached, the action potential does not occur. Increasing the strength of a stimulus (such as pressing harder with the pin) does not change the strength of an action potential. However, it may cause more action potentials to occur in a given period. As a result, the person may perceive that pain has increased.

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The myelin sheath • A lipid covering on long axons that acts to increase the speed of nerve impulse conduction, insulation for both CNS and PNS, and regeneration in the PNS • Schwann cells – neuroglia that make up the myelin sheath in the PNS • Oligodendrocytes- neuroglia that make up the myelin sheath in the CNS • Nodes of Ranvier – gaps between myelination on the axons • Saltatory conduction – conduction of the nerve impulse from node to node

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Myelin Sheath

Answer 310

role in CNS

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Primary Motor Area

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What is an interneuron?

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reasoning critical thinking formulating appropriate behaviors

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The spinal cord is the center for * thousands of reflex arcs . 1. stimulus causes **sensory receptors** to **generate signals** that travel in **sensory axons to the spinal cord.** 2. **Interneurons** integrate the incoming data and relay signals to **motor neurons**. 3. A response to the stimulus occurs when **motor axons** cause skeletal muscles to contract. 4. Motor neurons in a reflex arc may also affect smooth muscle, organs, or glands. 5. Each interneuron in the spinal cord synapses with numerous other neurons. 6. From there, interneurons send signals to other interneurons and motor neurons. Similarly, the spinal cord creates reflex arcs for the internal organs. 1. For example, when blood pressure falls, 2. internal receptors in the carotid arteries and aorta generate nerve signals that pass through sensory fibers to the cord 3. and then up an ascending tract 4. to a cardiovascular center in the brain. 5. Thereafter, nerve signals pass down a descending tract to the spinal cord. 6. Motor signals then cause blood vessels to constrict, so that the blood pressure rises.

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The small swelling at the end of an axon, which lies close to the dendrite or cell body of another neuron, is the axon

Answer 316

14.2 The Central Nervous System LEARNING OUTCOMES Upon completion of this section, you should be able to Identify the structures of the spinal cord and provide a function for each. Identify the structures of the brain and provide a function for each. Identify the lobes and major areas of the human brain. Distinguish between the functions of the primary motor and the primary somatosensory areas of the brain. The spinal cord and the brain make up the CNS, where sensory information is received and motor control is initiated. Both the spinal cord and the brain are protected by bone. The spinal cord is surrounded by vertebrae, and the brain is enclosed by the skull. Also, both the spinal cord and the brain are wrapped in protective Page 287membranes known as meninges (sing., meninx). Meningitis is an infection of the meninges and may be caused by either bacterial or viral pathogens. The spaces between the meninges are filled with cerebrospinal fluid, which cushions and protects the CNS. In a spinal tap (lumbar puncture), a small amount of this fluid is withdrawn from around the spinal cord for laboratory testing. Cerebrospinal fluid is also contained within the ventricles of the brain and in the central canal of the spinal cord. The brain has four ventricles, interconnecting chambers that produce and serve as a reservoir for cerebrospinal fluid (Fig. 14.7). Normally, any excess cerebrospinal fluid drains away into the cardiovascular system. However, blockages can occur. In an infant, the brain can enlarge due to cerebrospinal fluid accumulation, resulting in a condition called hydrocephalus (“water on the brain”). If cerebrospinal fluid collects in an adult, the brain cannot enlarge. Instead, it is pushed against the skull. Such situations cause severe brain damage and can be fatal unless quickly corrected. Figure 14.7 The ventricles of the brain. The brain has four ventricles. A lateral ventricle is found on each side of the brain. They join at the third ventricle. The third ventricle connects with the fourth ventricle superiorly; the central canal of the spinal cord joins the fourth ventricle inferiorly. All structures are filled with cerebrospinal fluid. a. Lateral view of ventricles seen through a transparent brain. b. Anterior view of ventricles seen through a transparent brain. The CNS is composed of two types of nervous tissue—gray matter and white matter. Gray matter contains cell bodies and short, nonmyelinated axons. White matter contains myelinated axons that run together in bundles called tracts. The Spinal Cord The spinal cord extends from the base of the brain through a large opening in the skull called the foramen magnum (see Fig. 12.4). From the foramen magnum, the spinal cord proceeds inferiorly in the vertebral canal. Structure of the Spinal Cord A cross-section of the spinal cord (Fig. 14.8a) shows a central canal, gray matter, and white matter. Figure 14.8b shows how an individual vertebra protects the spinal cord. The spinal nerves project from the cord through small openings called intervertebral foramina. Fibrocartilage intervertebral discs separate the vertebrae. If a disc ruptures or herniates, it may compress a spinal nerve, resulting in pain and a loss of mobility. Figure 14.8 The organization of white and gray matter in the spinal cord and the spinal nerves. a. Cross-section of the spinal cord, showing arrangements of white and gray matter. b. Spinal nerves originating from the spinal cord. c. The spinal cord is protected by vertebrae. d. Spinal nerves emerging from the cord. (a): ©Scientifica/Corbis Documentary/Getty Images; (d): ©McGraw-Hill Education/Rebecca Gray, photographer & Don Kincaid, dissections The central canal of the spinal cord contains cerebrospinal fluid, as do the meninges that protect the spinal cord. The gray matter is centrally located and shaped like the letter H (Fig. 14.8a–c). Portions of sensory neurons and motor neurons are found in gray matter, as are interneurons that communicate with these two types of neurons. The dorsal root of a spinal nerve contains sensory fibers entering the gray matter. The ventral root of a spinal nerve contains motor fibers exiting the gray matter. The dorsal and ventral roots join before the spinal nerve leaves the vertebral canal (Fig. 14.8c, d), forming a mixed nerve. Spinal nerves are a part of the PNS. The white matter of the spinal cord occurs in areas around the gray matter. The white matter contains ascending tracts taking information to the brain (primarily located posteriorly) and descending tracts taking information from the brain (primarily located anteriorly). Many tracts cross just after they enter and exit the brain, so the left side of the brain controls the right side of the body. Likewise, the right side of the brain controls the left side of the body. Functions of the Spinal Cord The spinal cord provides a means of communication between the brain and the peripheral nerves that leave the cord. When someone touches your hand, sensory receptors generate nerve signals that pass through sensory fibers to the spinal cord and up ascending tracts to the brain (see Fig. 14.2b, red arrows). The gate control theory of pain proposes that the tracts in the spinal cord have “gates” and that these gates control the flow of pain messages from the peripheral nerves to the brain. Depending on how the gates process a pain signal, the pain message can be allowed to pass directly to the brain or can be prevented from reaching the brain. Pain messages may also be blocked by other inputs, such as those received from touch receptors or endorphins. The brain coordinates the voluntary control of our limbs. Motor signals originating in the brain pass down descending tracts to the spinal cord and out to our muscles by way of motor fibers (see Fig. 14.2b, black arrows). Therefore, if the spinal cord is severed, we suffer a loss of sensation and a loss of voluntary control—paralysis. If the cut occurs in the thoracic region, the lower body and legs are paralyzed, a condition known as paraplegia. If the injury is in the neck region, all four limbs are usually affected, a condition called quadriplegia. Page 288 Reflex Actions The spinal cord is the center for thousands of reflex arcs (see Fig. 14.17). A stimulus causes sensory receptors to generate signals that travel in sensory axons to the spinal cord. Interneurons integrate the incoming data and relay signals to motor neurons. A response to the stimulus occurs when motor axons cause skeletal muscles to contract. Motor neurons in a reflex arc may also affect smooth muscle, organs, or glands. Each interneuron in the spinal cord synapses with numerous other neurons. From there, interneurons send signals to other interneurons and motor neurons. Similarly, the spinal cord creates reflex arcs for the internal organs. For example, when blood pressure falls, internal receptors in the carotid arteries and aorta generate nerve signals that pass through sensory fibers to the cord and then up an ascending tract to a cardiovascular center in the brain. Thereafter, nerve signals pass down a descending tract to the spinal cord. Motor signals then cause blood vessels to constrict, so that the blood pressure rises. The Brain The human brain has been called the last great frontier of biology. The goal of modern neuroscience is to understand the structure and function of the brain’s various parts so well that it will be possible to prevent or correct the thousands of mental disorders that rob humans of a normal life. This section gives only a glimpse of what is known about the brain and the modern avenues of research. We discuss the parts of the brain with reference to the cerebrum, the diencephalon, the cerebellum, and the brain stem. The brain’s four ventricles (see Fig. 14.7) are called, in turn, the two lateral ventricles, the third ventricle, and the fourth ventricle. It may be helpful for you to associate the cerebrum with the two lateral ventricles, the diencephalon with the third ventricle, and the brain stem and cerebellum with the fourth ventricle (Fig. 14.9a). Figure 14.9 The human brain. a. The cerebrum is the largest part of the brain in humans. b. Viewed from above, the cerebrum has left and right cerebral hemispheres. The hemispheres are connected by the corpus callosum. (b): ©McGraw-Hill Education; photo and dissection by Christine Eckel The Cerebrum The cerebrum is the largest portion of the brain in mammals, including humans. The cerebrum is the last center to receive sensory input and carry out integration before commanding voluntary motor responses. It communicates with and coordinates the activities of the other parts of the brain. Cerebral Hemispheres Just as the human body has two halves, so does the cerebrum. These halves are called the left and right cerebral hemispheres (Fig. 14.9b). A deep groove called the longitudinal fissure divides the left and right cerebral hemispheres. The two cerebral hemispheres communicate via the corpus callosum, an extensive bridge of nerve tracts. Page 289The characteristic appearance of the cerebrum is the result of thick folds, called gyri (sing., gyrus) separated by shallow grooves called sulci (sing., sulcus). The sulci divide each hemisphere into lobes (Fig. 14.10). The frontal lobe is the most anterior of the lobes (directly behind the forehead). The parietal lobe is posterior to the frontal lobe. The occipital lobe is posterior to the parietal lobe (at the rear of the head). The temporal lobe lies inferior to the frontal and parietal lobes (at the temple and the ear). Figure 14.10 The lobes of the cerebral hemispheres. Each cerebral hemisphere is divided into four lobes: frontal, parietal, temporal, and occipital. Centers in the frontal lobe control movement and higher reasoning, as well as the smell sensation. Somatic sensing is carried out by parietal lobe neurons, and those of the temporal lobe receive sound information. Visual information is received and processed in the occipital lobe. The Cerebral Cortex The cerebral cortex is a thin, highly convoluted outer layer of gray matter that covers the cerebral hemispheres. Recall that gray matter consists of neurons whose axons are not myelinated. The cerebral cortex contains over 1 billion cell bodies and is the region of the brain that accounts for sensation, voluntary movement, and all the thought processes we associate with consciousness. Primary Motor and Sensory Areas of the Cortex The cerebral cortex contains motor areas and sensory areas, as well as association areas. The primary motor area is in the frontal lobe just anterior to (before) the central sulcus. Voluntary commands to skeletal muscles begin in the primary motor area, and each part of the body is controlled by a certain section (Fig. 14.11a). In this illustration, notice that large areas of the cerebral cortex are devoted to controlling structures that carry out very fine, precise movements. Thus, the muscles that control facial movements—swallowing, salivation, expression—take up an especially large portion of the primary motor area. Likewise, hand movements require tremendous accuracy. Together, these two structures command nearly two-thirds of the primary motor area.Page 290 Figure 14.11 The primary motor and primary somatosensory areas of the brain. a. The primary motor area (blue) is located in the frontal lobe, adjacent to (b) the primary somatosensory area in the parietal lobe. The primary taste area is colored pink. The size of each body region shown indicates the relative amount of cortex devoted to control of that body region. SCIENCE IN YOUR LIFE Why does a stroke on the right side of the brain cause weakness or paralysis on the left side of the body? Descending motor tracts (from the primary motor area) and ascending sensory tracts (from the primary somatosensory area) cross over in the spinal cord and medulla. Motor neurons in the right cerebral hemisphere control the left side of the body and vice versa because of crossing-over. Likewise, sensation from the left half of the body travels to the right cerebral hemisphere. Destruction of brain tissue by a stroke interferes with outgoing motor signals to the opposite side of the body, as well as incoming sensory information from that side. The primary somatosensory area is just posterior to the central sulcus in the parietal lobe. Sensory information from the skin and skeletal muscles arrives here, where each part of the body is sequentially represented (Fig. 14.11b). Like the primary motor cortex, large areas of the primary sensory cortex are dedicated to those body areas with acute sensation. Once again, the face and hands require the largest proportion of the sensory cortex. Page 291Reception areas for the other primary sensations—taste, vision, hearing, and smell—are located in other areas of the cerebral cortex (see Fig. 14.10). The primary taste area in the parietal lobe (pink) accounts for taste sensations. Visual information is received by the primary visual cortex (blue) in the occipital lobe. The primary auditory area in the temporal lobe (green) accepts information from our ears. Smell sensations travel to the primary olfactory area (yellow) found on the deep surface of the frontal lobe. Association Areas Association areas are places where integration occurs and where memories are stored. Anterior to the primary motor area is a premotor area. The premotor area organizes motor functions for skilled motor activities, such as walking and talking at the same time. Next, the primary motor area sends signals to the cerebellum, which integrates them. A momentary lack of oxygen during birth can damage the motor areas of the cerebral cortex, resulting in cerebral palsy, a condition characterized by a spastic weakness of the arms and legs. The somatosensory association area, located just posterior to the primary somatosensory area, processes and analyzes sensory information from the skin and muscles. The visual association area in the occipital lobe associates new visual information with stored visual memories. It might “decide,” for example, if we have seen a face, scene, or symbol before. The auditory association area in the temporal lobe performs the same functions with regard to sounds. Processing Centers Processing centers of the cortex receive information from the other association areas and perform higher-level analytical functions. The prefrontal area, an association area in the frontal lobe, receives information from the other association areas and uses this information to reason and plan our actions. Integration in this area accounts for our most cherished human abilities. Reasoning, critical thinking, and formulating appropriate behaviors are possible because of integration carried out in the prefrontal area. The unique ability of humans to speak is partially dependent on two processing centers found only in the left cerebral cortex. Wernicke’s area is located in the posterior part of the left temporal lobe. Broca’s area is located in the left frontal lobe. Broca’s area is just anterior to the portion of the primary motor area for speech musculature (lips, tongue, larynx, and so forth) (see Fig. 14.10). Wernicke’s area helps us understand both the written and the spoken word and sends the information to Broca’s area. Broca’s area adds grammatical refinements and directs the primary motor area to stimulate the appropriate muscles for speaking and writing. Central White Matter Much of the rest of the cerebrum is composed of white matter. Myelination occurs and white matter develops as a child grows. Progressive myelination enables the brain to grow in size and complexity. For example, as neurons become myelinated within tracts designed for language development, children become more capable of speech. Descending tracts from the primary motor area communicate with lower brain centers, and ascending tracts from lower brain centers send sensory information up to the primary somatosensory area. Tracts within the cerebrum also take information among the different sensory, motor, and association areas pictured in Figure 14.10. The corpus callosum contains tracts that join the two cerebral hemispheres. Basal Nuclei Though the majority of each cerebral hemisphere is composed of tracts, there are masses of gray matter deep within the white matter. These basal nuclei integrate motor commands to ensure that the proper muscle groups are stimulated or inhibited. Integration ensures that movements are coordinated and smooth. Parkinson disease (see Section 18.5) is believed to be caused by degeneration of specific neurons in the basal nuclei. The Diencephalon The hypothalamus and thalamus are in the diencephalon, a region that encircles the third ventricle. The hypothalamus forms the floor of the third ventricle. The hypothalamus is an integrating center that helps maintain homeostasis. It regulates hunger, sleep, thirst, body temperature, and water balance. The hypothalamus controls the pituitary gland and thereby serves as a link between the nervous and endocrine systems. The thalamus consists of two masses of gray matter located in the sides and roof of the third ventricle. The thalamus is on the receiving end for all sensory input except the sense of smell. Visual, auditory, and somatosensory information arrives at the thalamus via the cranial nerves and tracts from the spinal cord. The thalamus integrates this information and sends it on to the appropriate portions of the cerebrum. The thalamus is involved in arousal of the cerebrum, and it participates in higher mental functions, such as memory and emotions. The pineal gland, which secretes the hormone melatonin, is located in the diencephalon. Presently, there is much popular interest in the role of melatonin in our daily rhythms. Some researchers believe it can help alleviate jet lag or insomnia. Scientists are also interested in the possibility that the hormone may regulate the onset of puberty. The Cerebellum The cerebellum lies under the occipital lobe of the cerebrum and is separated from the brain stem by the fourth ventricle. The cerebellum has two portions joined by a narrow median portion. Each portion is primarily composed of white matter. In a longitudinal section, the white matter has a treelike pattern called arbor vitae. Overlying the white matter is a thin layer of gray matter that forms a series of complex folds. The cerebellum receives sensory input from the eyes, ears, joints, and muscles about the present position of body parts. It also receives motor output from the cerebral cortex about where these parts should be located. After integrating this information, the cerebellum sends motor signals by way of the brain stem to the skeletal muscles. In this way, the cerebellum maintains posture and balance. It also ensures that all the muscles work together to produce smooth, coordinated, voluntary movements. The cerebellum assists in the learning of new motor skills, such as playing the piano or hitting a baseball. The Brain Stem The tracts cross in the brain stem, which contains the midbrain, the pons, and the medulla oblongata (see Fig. 14.9a). The midbrain acts as a relay station for tracts passing between the cerebrum and Page 292the spinal cord or cerebellum. It also has reflex centers for visual, auditory, and tactile responses. The pons (“bridge” in Latin) contains bundles of axons traveling between the cerebellum and the rest of the CNS. In addition, the pons functions with the medulla oblongata to regulate breathing rate. Reflex centers in the pons coordinate head movements in response to visual and auditory stimuli. The medulla oblongata contains a number of reflex centers for regulating heartbeat, breathing, and vasoconstriction (blood pressure). It also contains the reflex centers for vomiting, coughing, sneezing, hiccuping, and swallowing. The medulla oblongata lies just superior to the spinal cord, and it contains tracts that ascend or descend between the spinal cord and higher brain centers. Recall that tracts are groups of axons that travel together. Ascending tracts convey sensory information. Motor information is transmitted on descending tracts. The Reticular Formation The reticular formation is a complex network of nuclei, which are masses of gray matter, and fibers that extends the length of the brain stem (Fig. 14.12). The reticular formation is a major component of the reticular activating system (RAS). The RAS receives sensory signals and sends them to higher centers. Motor signals received by the RAS are sent to the spinal cord. Figure 14.12 The reticular formation of the brain. The reticular formation receives and sends on motor and sensory information to various parts of the CNS. One portion, the reticular activating system (RAS) (see arrows), arouses the cerebrum and, in this way, controls alertness versus sleep. The RAS arouses the cerebrum via the thalamus and causes a person to be alert. If you want to awaken the RAS, surprise it with sudden stimuli, such as an alarm clock ringing, bright lights, smelling salts, or cold water splashed on your face. The RAS can filter out unnecessary sensory stimuli, explaining why you can study with the TV on. Similarly, the RAS allows you to take a test without noticing the sounds of the people around you—unless the sounds are particularly distracting. To inactivate the RAS, remove visual or auditory stimuli, allowing yourself to become drowsy and drop off to sleep. General anesthetics function by artificially suppressing the RAS. A severe injury to the RAS can cause a person to become comatose, from which recovery may be impossible. CHECK YOUR PROGRESS 14.2 List the functions of the spinal cord. Answer Provides a means of communication between the brain and the peripheral nerves, and is the center for reflex actions. Summarize the major regions of the brain and describe the general function of each. Answer Cerebrum—largest part of the brain, integrates sensory inputs and coordinates the activities of the other parts of the brain; diencephalon—contains the hypothalamus and thalamus, maintains homeostasis, receives sensory input; cerebellum—sends out motor impulses by way of the brain stem to the skeletal muscles, produces smooth, coordinated voluntary movements; brain stem—contains the midbrain, pons, and medulla oblongata, acts as a relay station, and the medulla has reflex centers. Relate how the RAS aids in homeostasis. Answer The RAS regulates a person’s alertness, relays sensory signals to higher centers, and filters out unnecessary stimuli, which are important functions in being properly responsive to one’s environment. CONNECTING THE CONCEPTS For more information on the central nervous system, refer to the following discussions: Section 10.5 examines how the central nervous system controls breathing. Section 18.5 explores how aging and diseases such as Alzheimer disease influence the brain. Sections 23.3 and 23.4 outline how the size of the brain has changed over the course of human evolution.

Answer 317

The CNS generates motor output. Nerve signals from the CNS go by way of the PNS to the muscles, glands, and organs, all in response to the cookies. Signals to the salivary glands make you salivate. Your stomach generates the acid and enzymes Page 281needed to digest the cookies—even before you’ve had a bite. The CNS also coordinates the movement of your arms and hands as you reach for the cookies.

Answer 318

What are basal nuclei? **What is Parkinson disease** (see Section 18.5)

Answer 319

* electrochemical changes that convey information within the nervous system.

Answer 320

* This is a complex network of nuclei--masses of gray matter--and fibers that extends the length of the brain stem * major component of the **_reticular activating system_** (RAS): receives sensory signals and sends them to higher centers. * Motor signals received by the RAS are sent to the spinal cord. * arouses the cerebrum via the thalamus and causes a person to be **alert.** If you want to awaken the RAS, surprise it with sudden stimuli, such as an alarm clock ringing, bright lights, smelling salts, or cold water splashed on your face. * The RAS can filter out unnecessary sensory stimuli, explaining why you can study with the TV on. * Similarly, the RAS allows you to take a test without noticing the sounds of the people around you—unless the sounds are particularly distracting. * To inactivate the RAS, remove visual or auditory stimuli, allowing yourself to become drowsy and drop off to sleep. * General anesthetics function by artificially suppressing the RAS. A severe injury to the RAS can cause a person to become comatose, from which recovery may be impossible.

Answer 321

1. As mentioned in Section 14.1, there are more than 100 known neurotransmitters. 2. The most widely studied neurotransmitters to date are acetylcholine, norepinephrine, dopamine, serotonin, and gamma-aminobutyric acid (GABA). * Acetylcholine is an essential CNS neurotransmitter for memory circuits in the limbic system. * Norepinephrine is important to dreaming, waking, and mood. * The neurotransmitter dopamine plays a central role in the brain’s regulation of mood. Dopamine is also the basal nuclei neurotransmitter that helps organize coordinated movements. * Serotonin is involved in thermoregulation, sleeping, emotions, and perception. * GABA is an abundant inhibitory neurotransmitter in the CNS

Answer 322

14.2 The Central Nervous System 10 The CNS: Spinal cord • Reflex arc: • Stimulus causes sensory receptors to generate afferent signals in sensory axons to the spinal cord • Interneurons in spinal cord integrate the information and relay the information to the efferent motor neurons • Motor neuron axons cause skeletal and/or smooth muscles to contract 14.2 The Central Nervous System 11 What does the spinal cord look like? Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. dorsal root dorsal root ventral root ventral root vertebra spinal cord white matter central canal gray matter gray matter white matter gray matter meninges ventral dorsal white matter central canal vertebra b. a. c. dorsal root ganglion spinal nerve dorsal root ganglion spinal nerve dorsal root branches dorsal root ganglion cut vertebrae d. Dorsal view of spinal cord and dorsal roots of spinal nerves. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a: © Karl E. Deckart/Phototake; d: © The McGraw-Hill Companies, Inc./Rebecca Gray, photographer and Don Kincaid, dissections Figure 14.7 The organization of white and gray matter in the spinal cord and the spinal nerves. 14.2 The Central Nervous S

Answer 323

1. Normally, any excess cerebrospinal fluid drains away into the cardiovascular system. However, blockages can occur.

Answer 324

Neuromodulators

Answer 325

Distinguish between the functions of the primary motor and the primary somatosensory areas of the brain.

Answer 326

1. In common: * (1) They usually function in an involuntary manner; * (2) they innervate all internal organs; and * (3) they use two neurons and one ganglion for each impulse. * The first neuron has a cell body within the CNS and a preganglionic fiber that enters the ganglion. * The second neuron has a cell body within a ganglion and a postganglionic fiber that leaves the ganglion. 1. Reflex actions: such as those that * regulate blood pressure * and breathing rate, * are especially important to the maintenance of homeostasis. 1. These reflexes begin when the **sensory neurons** in contact with **internal organs send messages to the CNS.** 2. They are **completed by motor neurons within the autonomic system.**

Answer 327

Propogation of an Action Potential

Answer 328

* emerge either side of the spinal cord * 31 pairs * The roots physically **_separate the axons of sensory neurons from the axons of motor neurons:_** forming an arrangement resembling a letter **Y**. * The **posterior root** contains **sensory** fibers that direct sensory receptor information inward (toward the spinal cord). * The **cell body** of a sensory neuron is in a **posterior-root ganglion** (also termed a dorsal-root ganglion). * The **anterior** (also termed ventral) root of a spinal nerve contains motor fibers that conduct impulses outward (away from the cord) to the effecto**rs.** * **Observe in Figure 14.8** * that the anterior and posterior roots join to form a spinal nerve. * All spinal nerves are called mixed nerves, because they contain both sensory and motor fibers. * Each spinal nerve serves the particular region of the body in which it is located. * For example, the intercostal muscles of the rib cage are innervated by thoracic nerves.

Answer 329

Figure 14.7 The ventricles of the brain. The brain has four ventricles. A lateral ventricle is found on each side of the brain. They join at the third ventricle. The third ventricle connects with the fourth ventricle superiorly; the central canal of the spinal cord joins the fourth ventricle inferiorly. All structures are filled with cerebrospinal fluid. a. Lateral view of ventricles seen through a transparent brain. b. Anterior view of ventricles seen through a transparent brain. The CNS is composed of two types of nervous tissue—gray matter and white matter. Gray matter contains cell bodies and short, nonmyelinated axons. White matter contains myelinated axons that run together in bundles called tracts.

Answer 330

Check Yourself

Answer 331

1. posterior to the central sulcus in the parietal lobe. 2. Sensory information from the **_skin and skeletal muscles_** arrives here, where each part of the body is sequentially represented 3. . Like the primary motor cortex, large areas of the primary sensory cortex are dedicated to those body areas with **_acute sensation_**. 4. Once again, the **_face and hands_** require the largest proportion of the sensory cortex. 5. Reception areas for the other primary sensations—**taste, vision, hearing, and smell**—are located in other areas of the cerebral cortex (see Fig. 14.10). 1. The primary taste area in the parietal lobe (pink) accounts for taste sensations. 2. Visual information is received by the primary visual cortex (blue) in the occipital lobe. 3. The primary auditory area in the temporal lobe (green) accepts information from our ears. 4. Smell sensations travel to the primary olfactory area (yellow) found on the deep surface of the frontal lobe.

Answer 332

* vary in appearance, but all of them have * three distinct structures: 1. a **_cell body_**: contains the nucleus, as well as other organelles. 2. **_dendrites_**: short extensions that receive signals from sensory receptors or other neurons. Incoming signals from dendrites can result in nerve signals that are then conducted by an axon. T. 3. **_axon_**: portion of a neuron that conducts nerve impulses; quite long. Individual axons are termed nerve fibers, and collectively they form a nerve **_Myelin Sheath_** * plays an important role in the rate at which signals move through the neuron. * Many axons covered by this protective sheath * develops when **_Schwann cells (PNS)_** or **_oligodendrocytes (CNS)_** wrap their **membranes** around an **axon** many times. * Each **neuroglia** cell covers only a portion of an axon, so the myelin sheath is interrupted. * The gaps where there is no myelin sheath are called **_nodes of Ranvier_**. Later in this section, we will see how the myelin sheath

Answer 333

Spinal cord

Answer 334

* Like mental illness, drug abuse is linked to _neurotransmitter levels._ * dopamine -- mood regulation. * Dopamine plays a central role in the working of the brain’s **built-in reward** circuit. * The reward circuit is a collection of neurons that, under normal circumstances, **promotes healthy, pleasurable activities,** such as consuming food. * behaviors stimulate the reward circuit and make us feel good. * Drug abusers take drugs that **artificially affect the reward circuit** to the point that they **neglect their basic physical needs in favor of continued drug use.** 1. Drug abuse is apparent when a person takes a drug at a dose level and under circumstances that increase the potential for a harmful effect. 2. Drug abusers are apt to display a psychological and/or physical dependence on the drug. 3. Psychological dependence is apparent when a person craves the drug, spends time seeking the drug, and takes it regularly. 4. With physical dependence, formerly called “addiction,” the person has become tolerant to the drug. 5. More is needed to get the same effect, and withdrawal symptoms occur when he or she stops taking the drug. This is true for not only teenagers and adults but also newborn babies of mothers who abuse and are addicted to drugs. Alcohol, drugs, and tobacco can all adversely affect the developing embryo, fetus, or newborn.

Answer 335

1. An action potential arrives at the axon terminal and 2. calcium enters the terminal. 3. Synaptic vesicles enclosing the neurotransmitter fuse with the sending neuron’s membrane. 4. Neurotransmitters are released, travel across the synapse, and bind to receptors on the receiving neuron membrane. 5. Sodium diffuses into the receiving neuron, and an action potential is created.

Answer 336

Drug Abuse

Answer 337

1. I regulate : * hunger, * sleep, * thirst, * body temperature, * and water balance.

Answer 338

Reticular Formation

Answer 339

1. branched cells that wrap CNS nerve fibers 2. Produce fatty insulating coverings (myelin sheath) around nerve fibers in the CNS – Can coil around as many as 60 different fibers at one time

Answer 340

Primary Motor and Sensory Areas of the Cortex The cerebral cortex contains motor areas and sensory areas, as well as association areas. The primary motor area is in the frontal lobe just anterior to (before) the central sulcus. Voluntary commands to skeletal muscles begin in the primary motor area, and each part of the body is controlled by a certain section (Fig. 14.11a). In this illustration, notice that large areas of the cerebral cortex are devoted to controlling structures that carry out very fine, precise movements. Thus, the muscles that control facial movements—swallowing, salivation, expression—take up an especially large portion of the primary motor area. Likewise, hand movements require tremendous accuracy. Together, these two structures command nearly two-thirds of the primary motor area.Page 290 Figure 14.11 The primary motor and primary somatosensory areas of the brain. a. The primary motor area (blue) is located in the frontal lobe, adjacent to (b) the primary somatosensory area in the parietal lobe. The primary taste area is colored pink. The size of each body region shown indicates the relative amount of cortex devoted to control of that body region. SCIENCE IN YOUR LIFE Why does a stroke on the right side of the brain cause weakness or paralysis on the left side of the body? Descending motor tracts (from the primary motor area) and ascending sensory tracts (from the primary somatosensory area) cross over in the spinal cord and medulla. Motor neurons in the right cerebral hemisphere control the left side of the body and vice versa because of crossing-over. Likewise, sensation from the left half of the body travels to the right cerebral hemisphere. Destruction of brain tissue by a stroke interferes with outgoing motor signals to the opposite side of the body, as well as incoming sensory information from that side. The primary somatosensory area is just posterior to the central sulcus in the parietal lobe. Sensory information from the skin and skeletal muscles arrives here, where each part of the body is sequentially represented (Fig. 14.11b). Like the primary motor cortex, large areas of the primary sensory cortex are dedicated to those body areas with acute sensation. Once again, the face and hands require the largest proportion of the sensory cortex. Page 291Reception areas for the other primary sensations—taste, vision, hearing, and smell—are located in other areas of the cerebral cortex (see Fig. 14.10). The primary taste area in the parietal lobe (pink) accounts for taste sensations. Visual information is received by the primary visual cortex (blue) in the occipital lobe. The primary auditory area in the temporal lobe (green) accepts information from our ears. Smell sensations travel to the primary olfactory area (yellow) found on the deep surface of the frontal lobe. Association Areas Association areas are places where integration occurs and where memories are stored. Anterior to the primary motor area is a premotor area. The premotor area organizes motor functions for skilled motor activities, such as walking and talking at the same time. Next, the primary motor area sends signals to the cerebellum, which integrates them. A momentary lack of oxygen during birth can damage the motor areas of the cerebral cortex, resulting in cerebral palsy, a condition characterized by a spastic weakness of the arms and legs. The somatosensory association area, located just posterior to the primary somatosensory area, processes and analyzes sensory information from the skin and muscles. The visual association area in the occipital lobe associates new visual information with stored visual memories. It might “decide,” for example, if we have seen a face, scene, or symbol before. The auditory association area in the temporal lobe performs the same functions with regard to sounds. Processing Centers Processing centers of the cortex receive information from the other association areas and perform higher-level analytical functions. The prefrontal area, an association area in the frontal lobe, receives information from the other association areas and uses this information to reason and plan our actions. Integration in this area accounts for our most cherished human abilities. Reasoning, critical thinking, and formulating appropriate behaviors are possible because of integration carried out in the prefrontal area. The unique ability of humans to speak is partially dependent on two processing centers found only in the left cerebral cortex. Wernicke’s area is located in the posterior part of the left temporal lobe. Broca’s area is located in the left frontal lobe. Broca’s area is just anterior to the portion of the primary motor area for speech musculature (lips, tongue, larynx, and so forth) (see Fig. 14.10). Wernicke’s area helps us understand both the written and the spoken word and sends the information to Broca’s area. Broca’s area adds grammatical refinements and directs the primary motor area to stimulate the appropriate muscles for speaking and writing. Central White Matter Much of the rest of the cerebrum is composed of white matter. Myelination occurs and white matter develops as a child grows. Progressive myelination enables the brain to grow in size and complexity. For example, as neurons become myelinated within tracts designed for language development, children become more capable of speech. Descending tracts from the primary motor area communicate with lower brain centers, and ascending tracts from lower brain centers send sensory information up to the primary somatosensory area. Tracts within the cerebrum also take information among the different sensory, motor, and association areas pictured in Figure 14.10. The corpus callosum contains tracts that join the two cerebral hemispheres. Basal Nuclei Though the majority of each cerebral hemisphere is composed of tracts, there are masses of gray matter deep within the white matter. These basal nuclei integrate motor commands to ensure that the proper muscle groups are stimulated or inhibited. Integration ensures that movements are coordinated and smooth. Parkinson disease (see Section 18.5) is believed to be caused by degeneration of specific neurons in the basal nuclei. The Diencephalon The hypothalamus and thalamus are in the diencephalon, a region that encircles the third ventricle. The hypothalamus forms the floor of the third ventricle. The hypothalamus is an integrating center that helps maintain homeostasis. It regulates hunger, sleep, thirst, body temperature, and water balance. The hypothalamus controls the pituitary gland and thereby serves as a link between the nervous and endocrine systems. The thalamus consists of two masses of gray matter located in the sides and roof of the third ventricle. The thalamus is on the receiving end for all sensory input except the sense of smell. Visual, auditory, and somatosensory information arrives at the thalamus via the cranial nerves and tracts from the spinal cord. The thalamus integrates this information and sends it on to the appropriate portions of the cerebrum. The thalamus is involved in arousal of the cerebrum, and it participates in higher mental functions, such as memory and emotions. The pineal gland, which secretes the hormone melatonin, is located in the diencephalon. Presently, there is much popular interest in the role of melatonin in our daily rhythms. Some researchers believe it can help alleviate jet lag or insomnia. Scientists are also interested in the possibility that the hormone may regulate the onset of puberty. The Cerebellum The cerebellum lies under the occipital lobe of the cerebrum and is separated from the brain stem by the fourth ventricle. The cerebellum has two portions joined by a narrow median portion. Each portion is primarily composed of white matter. In a longitudinal section, the white matter has a treelike pattern called arbor vitae. Overlying the white matter is a thin layer of gray matter that forms a series of complex folds. The cerebellum receives sensory input from the eyes, ears, joints, and muscles about the present position of body parts. It also receives motor output from the cerebral cortex about where these parts should be located. After integrating this information, the cerebellum sends motor signals by way of the brain stem to the skeletal muscles. In this way, the cerebellum maintains posture and balance. It also ensures that all the muscles work together to produce smooth, coordinated, voluntary movements. The cerebellum assists in the learning of new motor skills, such as playing the piano or hitting a baseball. The Brain Stem The tracts cross in the brain stem, which contains the midbrain, the pons, and the medulla oblongata (see Fig. 14.9a). The midbrain acts as a relay station for tracts passing between the cerebrum and Page 292the spinal cord or cerebellum. It also has reflex centers for visual, auditory, and tactile responses. The pons (“bridge” in Latin) contains bundles of axons traveling between the cerebellum and the rest of the CNS. In addition, the pons functions with the medulla oblongata to regulate breathing rate. Reflex centers in the pons coordinate head movements in response to visual and auditory stimuli. The medulla oblongata contains a number of reflex centers for regulating heartbeat, breathing, and vasoconstriction (blood pressure). It also contains the reflex centers for vomiting, coughing, sneezing, hiccuping, and swallowing. The medulla oblongata lies just superior to the spinal cord, and it contains tracts that ascend or descend between the spinal cord and higher brain centers. Recall that tracts are groups of axons that travel together. Ascending tracts convey sensory information. Motor information is transmitted on descending tracts. The Reticular Formation The reticular formation is a complex network of nuclei, which are masses of gray matter, and fibers that extends the length of the brain stem (Fig. 14.12). The reticular formation is a major component of the reticular activating system (RAS). The RAS receives sensory signals and sends them to higher centers. Motor signals received by the RAS are sent to the spinal cord. Figure 14.12 The reticular formation of the brain. The reticular formation receives and sends on motor and sensory information to various parts of the CNS. One portion, the reticular activating system (RAS) (see arrows), arouses the cerebrum and, in this way, controls alertness versus sleep. The RAS arouses the cerebrum via the thalamus and causes a person to be alert. If you want to awaken the RAS, surprise it with sudden stimuli, such as an alarm clock ringing, bright lights, smelling salts, or cold water splashed on your face. The RAS can filter out unnecessary sensory stimuli, explaining why you can study with the TV on. Similarly, the RAS allows you to take a test without noticing the sounds of the people around you—unless the sounds are particularly distracting. To inactivate the RAS, remove visual or auditory stimuli, allowing yourself to become drowsy and drop off to sleep. General anesthetics function by artificially suppressing the RAS. A severe injury to the RAS can cause a person to become comatose, from which recovery may be impossible. CHECK YOUR PROGRESS 14.2 List the functions of the spinal cord. Answer Provides a means of communication between the brain and the peripheral nerves, and is the center for reflex actions. Summarize the major regions of the brain and describe the general function of each. Answer Cerebrum—largest part of the brain, integrates sensory inputs and coordinates the activities of the other parts of the brain; diencephalon—contains the hypothalamus and thalamus, maintains homeostasis, receives sensory input; cerebellum—sends out motor impulses by way of the brain stem to the skeletal muscles, produces smooth, coordinated voluntary movements; brain stem—contains the midbrain, pons, and medulla oblongata, acts as a relay station, and the medulla has reflex centers. Relate how the RAS aids in homeostasis. Answer The RAS regulates a person’s alertness, relays sensory signals to higher centers, and filters out unnecessary stimuli, which are important functions in being properly responsive to one’s environment. CONNECTING THE CONCEPTS For more information on the central nervous system, refer to the following discussions: Section 10.5 examines how the central nervous system controls breathing. Section 18.5 explores how aging and diseases such as Alzheimer disease influence the brain. Sections 23.3 and 23.4 outline how the size of the brain has changed over the course of human evolution.

Answer 341

Neuromodulators are naturally occurring molecules that block the release of a neurotransmitter or modify a neuron’s response to a neurotransmitter. Two well-known neuromodulators are substance P and endorphins. Substance P is a neuropeptide that is released by sensory neurons when pain is present. Endorphins block the release of substance P and serve as natural painkillers. Endorphins are produced by the brain during times of physical and/or emotional stress. They are associated with the “runner’s high” of joggers. Both pharmaceuticals and illegal drugs have several basic modes of action: They promote the action of a neurotransmitter, usually by increasing the amount of neurotransmitter at a synapse. Examples include drugs such as alprazolam (Xanax) and diazepam (Valium), which increase GABA. These medications are used for panic attacks and anxiety. Reduced levels of norepinephrine and serotonin are linked to depression. Drugs such as fluoxetine (Prozac), paroxetine (Paxil), and duloxetine (Cymbalta) allow norepinephrine and/or serotonin to accumulate at the synapse, which explains their effectiveness as antidepressants. Alzheimer disease causes a slow, progressive loss of memory (see Section 18.5). Drugs used for Alzheimer disease allow acetylcholine to accumulate at synapses in the limbic system. They interfere with or decrease the action of a neurotransmitter. For instance, antipsychotic drugs used for the treatment of schizophrenia decrease the activity of dopamine. The caffeine in coffee, chocolate, and tea keeps us awake by interfering with the effects of inhibitory neurotransmitters in the brain. They replace or mimic a neurotransmitter or neuromodulator. The opiates—namely, codeine, heroin, and morphine—bind to endorphin receptors and in this way reduce pain and produce a feeling of well-being. Ongoing research into neurophysiology and neuropharmacology (the study of nervous system function and the way drugs work in the nervous system) continues to provide evidence that mental illnesses are caused by imbalances in neurotransmitters. These studies will undoubtedly improve treatments for mental illness, as well as provide insight into the problem of drug abuse.

Answer 342

1. integration occurs 2. memories are stored. 3. **_premotor area._** * **__***Anterior to the primary motor area* * **organizes motor functions** for **_skilled motor activities_**, * such as walking and talking at the same time. * Next, the **primary motor area** sends signals to the **cerebellum,** which _integrates them_. * A momentary lack of oxygen during birth can damage the motor areas of the cerebral cortex, resulting in **_cerebral palsy_**, a condition characterized by a spastic weakness of the arms and legs. 4. **_T_**he **_visual association area_** in the **occipital lobe** * **_processes and analyzes sensory information from the skin and muscles._** * just posterior to the primary somatosensory area, * *associates new visual information with stored visual memories.* It might “decide,” for example, if we have seen a face, scene, or symbol before. 1. The **auditory association area** in the **temporal lobe** performs the same functions with regard to **sounds**

Answer 343

The central nervous system • The CNS consists of the brain and spinal cord. • Both are protected by • Scalp and skin • Bones – skull and vertebral column • Meninges – 3 protective membranes that wrap around CNS • Cerebral spinal fluid (CSF) – space between meninges is filled with this fluid that cushions and protects the CNS • Blood brain barrier (BBB) Meninges • Dura mater • Double-layered external covering • Periosteum – dense connective tissue attached to surface of the skull • Meningeal layer – outer covering of the brain • Folds inward in several areas Meninges • Arachnoid mater • Middle layer • Web-like • Pia mater • Internal layer • Clings to the surface of the brain • Many blood vessels http://droualb.faculty.mjc.edu/Lecture%20Notes/Unit%205/Meninges\_peeled\_away

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Primary Motor and Sensory Areas of the Cortex The cerebral cortex contains motor areas and sensory areas, as well as association areas. The primary motor area is in the frontal lobe just anterior to (before) the central sulcus. Voluntary commands to skeletal muscles begin in the primary motor area, and each part of the body is controlled by a certain section (Fig. 14.11a). In this illustration, notice that large areas of the cerebral cortex are devoted to controlling structures that carry out very fine, precise movements. Thus, the muscles that control facial movements—swallowing, salivation, expression—take up an especially large portion of the primary motor area. Likewise, hand movements require tremendous accuracy. Together, these two structures command nearly two-thirds of the primary motor area.Page 290 Figure 14.11 The primary motor and primary somatosensory areas of the brain. a. The primary motor area (blue) is located in the frontal lobe, adjacent to (b) the primary somatosensory area in the parietal lobe. The primary taste area is colored pink. The size of each body region shown indicates the relative amount of cortex devoted to control of that body region.

Answer 345

Describe the relationship between the left and right sides of the brain and language and speech.

Answer 346

Summarize how a nerve impulse is transmitted from one neuron to the next.

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1. gray matter and white matter. 2. **Gray matter** contains cell bodies and short, nonmyelinated axons. 3. White matter contains myelinated axons that run together in bundles called **tracts**.

Answer 348

4.2 The Central Nervous System 19 Prefrontal Cortex • “CEO of the brain” • Where you control and plan your actions • Working memory • Organization • Modulate your mood • Conscience • Personality • Not fully developed until at least 25 years of age– maybe even later! (You can blame your bad decisions on this if you are younger than this-- ha!– or flip it around: drugs, alcohol, excessive videogaming, etc. can really have a permanent negative impact on this developing brain area even if you are of ‘legal age’…) 14.2 The Central Nervous System 20 1. The brain: Cerebrum – The cerebral cortex Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. salivation vocalization mastication longitudinal fissure facial expression swallowing thumb, fingers, and hand forearm arm trunk pelvis thigh leg foot and toes lips upper face

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* regulates the activity of * cardiac and smooth muscles * organs, and * glands. * * System: 1. sympathetic 2. parasympathetic divisions * Activation generally causes opposite responses in 2. * Shared features despite different functions: 1. usually function involuntarily 2. innervate all internal organs 3. they use two neurons and one ganglion for each impulse. 1. The first neuron has a cell body within the CNS and a preganglionic fiber that enters the ganglion. 2. The second neuron has a cell body within a ganglion and a postganglionic fiber that leaves the ganglion. * Reflex actions, such as those that regulate blood pressure and breathing rate, are especially important to the maintenance of **homeostasis.** These reflexes begin when the sensory neurons in contact with internal organs send messages to the CNS. They are **completed by motor neurons within the autonomic system.**

Answer 350

* The resting potential energy of the neuron can be used to perform the work of the neuron: conduction of nerve signals. * The process of conduction is termed an action potential, and it occurs in the axons of neurons: 1. A stimulus activates the neuron and begins the action potential. * For example, a stimulus for pain neurons in the skin would be the prick of a sharp pin. * However, the stimulus must be strong enough to cause the cell to reach **threshold**, the voltage that will result in an action potential. In Figure 14.4b, the threshold voltage is around −55 mV. * An action potential is an **all-or-nothing event.** * ****Once threshold is reached, the action potential happens automatically and completely. On the other hand, if the threshold voltage is never reached, the action potential does not occur. Increasing the strength of a stimulus (such as pressing harder with the pin) does not change the strength of an action potential. However, it may cause more action potentials to occur in a given period. As a result, the person may perceive that pain has increased.

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* white matter. Myelination occurs and white matter develops as a child grows. * **Progressive myelination** enables the brain to grow in size and complexity. For example, as neurons become myelinated within tracts designed for language development, children become more capable of speech. * **Descending tracts** from the primary motor area communicate with lower brain centers, and ascending tracts from lower brain centers send sensory information up to the primary somatosensory area. * Tracts take information among the different sensory, motor, and association areas pictured in Figure 14.10. The corpus callosum contains tracts that join the two cerebral hemispheres.

Answer 352

The Somatic System The PNS has divisions: the somatic system and the autonomic system. The nerves in the somatic system serve the skin, skeletal muscles, and tendons (see Fig. 14.2). The somatic system sensory nerves take sensory information from external sensory receptors to the CNS. Motor commands leaving the CNS travel to skeletal muscles via somatic motor nerves. Not all somatic motor actions are voluntary. Some are automatic. Automatic responses to a stimulus in the somatic system are called reflexes. A reflex occurs quickly, without your even having to think about it. For example, a reflex may cause you to blink your eyes in response to a flash of light, without your willing it. We will study the path of a reflex, because it allows us to study in detail the path of nerve signals to and from the CNS.Page 296 The Reflex Arc Figure 14.17 illustrates the path of a reflex that involves only the spinal cord. If your hand touches a sharp pin, sensory receptors in the skin generate nerve signals that move along sensory fibers through the posterior (dorsal) root ganglia toward the spinal cord. Sensory neurons that enter the cord posteriorly pass signals on to many interneurons. Some of these interneurons synapse with motor neurons whose short dendrites and cell bodies are in the spinal cord. Nerve signals travel along these motor fibers to an effector, which brings about a response to the stimulus. In this case, the effector is a muscle, which contracts so that you withdraw your hand from the pin. Various other reactions are also possible—you will most likely look at the pin, wince, and cry out in pain. This whole series of responses occurs because some of the interneurons involved carry nerve signals to the brain. The brain makes you aware of the stimulus and directs these other reactions to it. In other words, you don’t feel pain until the brain receives the information and interprets it.

Answer 353

14.3 The Limbic System and Higher Mental Functions LEARNING OUTCOMES Upon completion of this section, you should be able to Identify the structures of the limbic system. Explain how the limbic system is involved in memory, language, and speech. Summarize the types of memory associated with the limbic system.

Answer 354

The brain has 4 of these. This is where they are found This is where they join - this number ventricle the third and fourth ventricle join \_\_\_\_\_\_\_\_\_\_\_\_ The _______________ joins the 4th ventricle \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ All are filled with \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_. See/Download image

Answer 355

I work closely as a link between the nervous and endochrine systems.

Answer 356

* cortex **_receive information from the other association areas and perform higher-level analytical functions._** * The prefrontal area, an association area in the frontal lobe, receives information from the other association areas and uses this information to reason and plan our actions. Integration in this area accounts for our most cherished human abilities. * Reasoning, critical thinking, and formulating appropriate behaviors are possible because of integration carried out in the prefrontal area. * The unique ability of humans to speak is partially dependent on two processing centers found only in the left cerebral cortex. * **Wernicke’s area** is located in the **posterior part** of the left temporal lobe. * **Broca’s area** is located in the left frontal lobe. Broca’s area is just anterior to the portion of the primary motor area for **speech musculature (**lips, tongue, larynx, and so forth) (see Fig. 14.10). * **Wernicke’s area helps us understand both the written and the spoken word and sends the information to Broca’s area.** * **Broca’s area adds grammatical refinements and directs the primary motor area to**

Answer 357

The spinal cord and brain are protected by \_\_\_\_\_\_\_\_\_\_\_\_\_\_, with the spinal cord being surrounded by \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, and the brain enclosed by \_\_\_\_\_\_\_\_\_\_\_\_. They are both also wrapped in \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.

Answer 358

Spinal Cord Reflex Arcs for Internal Organs What are the steps of regulating blood pressure?

Answer 359

1. In myelinated fibers, an action potential at one node of Ranvier causes an action potential at the next, jumping over the entire myelin-coated portion of the axon: This type of conduction is translated from (saltatio is a Latin word that means “to jump”) and is much faster. In thick, myelinated fibers, the rate of transmission is more than 100 m/s. 2. Regardless of whether an axon is myelinated or not, its action potentials are self-propagating. Each action potential generates another, along the entire length of the axon. 3. Like the action potential itself, conduction of an action potential is an **all-or-none event**—either an axon conducts its action potential or it does not. The **intensity** of a message is determined by how many action potentials are generated within a given time. An axon can conduct a volley of action potentials very quickly, because only a small number of ions are exchanged with each action potential. Once the action potential is complete, the ions are rapidly restored to their proper place through the action of the sodium–potassium pump 4. Neural Transmission: Action Potential Propagation * As soon as the action potential has passed by each successive portion of an axon, that portion undergoes a **_short refractory period_**, during which it is unable to conduct an action potential. * This ensures the **one-way direction** of a signal from the cell body down the length of the axon to the axon terminal. \*\*\*a*ll functions of the nervous system, from our deepest emotions to our highest reasoning abilities, are dependent on the conduction of nerve signals\*\** **_Propagation of an Action Potential_** 1. If an axon is unmyelinated, an action potential at one locale stimulates an adjacent part of the axon membrane to produce an action potential. Conduction along the entire axon in this fashion can be rather slow—approximately 1 meter/second (1 m/s) in thin axons—because each section of the axon must be stimulated.

Answer 360

1. outside the nervous system, contains the nerves 1. cranial nerves when they arise from the brain and are termed 2. spinal nerves when they arise from the spinal cord. 3. In any case, all nerves carry signals to and from the CNS. 2. anatomy of a nerve: * The cell body and the dendrites of neurons are in either the CNS or the ganglia. * Ganglia (sing., ganglion) are collections of nerve cell bodies outside the CNS. * The axons of neurons project from the CNS and form the spinal cord. * In other words, nerves, whether cranial or spinal, are composed of axons, the long part of neurons. 1. 2. Humans have 12 pairs of cranial nerves attached to the brain. By convention, the pairs of cranial nerves are referred to by Roman numerals (Fig. 14.16). Some cranial nerves are sensory nerves—they contain only sensory fibers; some are motor nerves that contain only motor fibers; others are mixed nerves that contain both sensory and motor fibers. Cranial nerves are largely concerned with the head, neck, and facial regions of the body. However, the vagus nerve (X) has branches not only to the pharynx and larynx but also to most of the internal organs. It arises from the brain stem—specifically, the medulla oblongata, which communicates with the hypothalamus. These two parts of the brain control the internal organs. 3. Figure 14.16 The cranial nerves. Overall, cranial nerves receive sensory input from, and send motor outputs to, the head region. The spinal nerves receive sensory input from, and send motor outputs to, the rest of the body. Two important exceptions are the vagus nerve, X, which communicates with internal organs, and the spinal accessory nerve, XI, which controls neck and back muscles. 4. The spinal nerves of humans emerge from either side of the spinal cord (see Fig. 14.8). There are 31 pairs of spinal nerves. The roots of a spinal nerve physically separate the axons of sensory neurons from the axons of motor neurons, forming an arrangement resembling a letter Y. The posterior root of a spinal nerve contains sensory fibers that direct sensory receptor information inward (toward the spinal cord). The cell body of a sensory neuron is in a posterior-root ganglion (also termed a dorsal-root ganglion). The anterior (also termed ventral) root of a spinal nerve contains motor fibers that conduct impulses outward (away from the cord) to the effectors. Observe in Figure 14.8 that the anterior and posterior roots join to form a spinal nerve. All spinal nerves are called mixed nerves, because they contain both sensory and motor fibers. Each spinal nerve serves the particular region of the body in which it is located. For example, the intercostal muscles of the rib cage are innervated by thoracic nerves. 5.

Answer 361

Functional Classification of the Peripheral Nervous System  Sensory (afferent) division  Nerve fibers that carry information to the central nervous system  Motor (efferent) division  Nerve fibers that carry impulses away from the central nervous system  Somatic nervous system = voluntary (skeletal muscles)  Autonomic nervous system = involuntary (cardiac and smooth muscles, glands)

Answer 362

Somatic Versus Autonomic Systems

Answer 363

1. A single neuron has a cell body and may have many dendrites (Fig. 14.6a). All can have synapses with many other neurons. Therefore, a neuron is on the receiving end of many signals,which can either be excitatory or inhibitory. 2. Recall that an excitatory neurotransmitter produces an excitatory signal by opening sodium gates at a synapse. This drives the neuron closer to its threshold. If threshold is reached, an action potential is inevitable. On the other hand, an inhibitory neurotransmitter drives the neuron farther from an action potential (red line in Fig. 14.6b) by opening the gates for potassium. **_Neurons integrate these incoming signals_**. Integration is the summing up of excitatory and inhibitory signals. If a neuron receives enough excitatory signals (either from different synapses or at a rapid rate from a single synapse) to outweigh the inhibitory ones, chances are the axon will **transmit a signal.** On the other hand, if a neuron receives more inhibitory than excitatory signals, summing these signals may prohibit the axon from reaching threshold and then depolarizing (the solid black line in Fig. 14.6b).

Answer 364

Nerve Impulse Action Potential

Answer 365

What is the Limbic System and Higher Level Functions? What areas may work with lower centers to produce l**_earning and memory?_** This is the ability to hold a thought in mind or recall a word from yesterday? What are types of this Page 294

Answer 366

The Central Nervous System 1. The brain: Cerebrum –

Answer 367

The PNS: Somatic division • The somatic system serves the skin, skeletal muscles and tendons. • Automatic responses are called reflexes. • Reflexes consist of sensory receptorsensory neuron interneuron  motor neuron effector organ (we talked about this in 14.1)

Answer 368

These are the differences amongst neuron types insofar as structures

Answer 369

integrates our emotions with our higher mental functions contains the amygdala and hippocampus accounts for why eating and sexual behavior seem pleasurable

Answer 370

Both pharmaceuticals and illegal drugs have several basic modes of action: They promote the action of a neurotransmitter, usually by increasing the amount of neurotransmitter at a synapse. Examples include drugs such as alprazolam (Xanax) and diazepam (Valium), which increase GABA. These medications are used for panic attacks and anxiety. Reduced levels of norepinephrine and serotonin are linked to depression. Drugs such as fluoxetine (Prozac), paroxetine (Paxil), and duloxetine (Cymbalta) allow norepinephrine and/or serotonin to accumulate at the synapse, which explains their effectiveness as antidepressants. Alzheimer disease causes a slow, progressive loss of memory (see Section 18.5). Drugs used for Alzheimer disease allow acetylcholine to accumulate at synapses in the limbic system. They interfere with or decrease the action of a neurotransmitter. For instance, antipsychotic drugs used for the treatment of schizophrenia decrease the activity of dopamine. The caffeine in coffee, chocolate, and tea keeps us awake by interfering with the effects of inhibitory neurotransmitters in the brain. They replace or mimic a neurotransmitter or neuromodulator. The opiates—namely, codeine, heroin, and morphine—bind to endorphin receptors and in this way reduce pain and produce a feeling of well-being. Ongoing research into neurophysiology and neuropharmacology (the study of nervous system function and the way drugs work in the nervous system) continues to provide evidence that mental illnesses are caused by imbalances in neurotransmitters. These studies will undoubtedly improve treatments for mental illness, as well as provide insight into the problem of drug abuse.

Answer 371

Classified according to function, the three types of neurons are sensory neurons, interneurons, and motor neurons (Fig. 14.3). Their functions are best described relative to the CNS. A sensory neuron takes nerve signals from a sensory receptor to the CNS. Sensory receptors are special structures that detect changes in the environment. An interneuron lies entirely within the CNS. Interneurons can receive input from sensory neurons and from other interneurons in the CNS. Thereafter, they sum up all the information received from other neurons before they communicate with motor neurons. A motor neuron takes nerve impulses away from the CNS to an effector (muscle fiber, organ, or gland). Effectors carry out our responses to environmental changes, whether these are external or internal. Figure 14.3 The structure of sensory neurons, interneurons, and motor neurons. a. A sensory neuron has a long axon covered by a myelin sheath that takes nerve impulses all the way from dendrites to the CNS. b. In the CNS, some interneurons, such as this one, have a short axon that is not covered by a myelin sheath. c. A motor neuron has a long axon covered by a myelin sheath that takes nerve impulses from the CNS to an effector. (photos) (a): ©McGraw-Hill Education/Dr. Dennis Emery, Dept. of Zoology and Genetics, Iowa State University, photographer; (b): ©David M. Phillips/Science Source Neurons vary in appearance, but all of them have three distinct structures: a cell body, dendrites, and an axon. The cell body contains the nucleus, as well as other organelles. Dendrites are short extensions that receive signals from sensory receptors or other neurons. Incoming signals from dendrites can result in nerve signals that are then conducted by an axon. The axon is the portion of a neuron that conducts nerve impulses. An axon can be quite long. Individual axons are termed nerve fibers, and collectively they form a nerve. In sensory neurons, a very long axon carries nerve signals from the dendrites associated with a sensory receptor to the CNS, and this axon is interrupted by the cell body. In interneurons and motor neurons, on the other hand, multiple dendrites take signals to the cell body, and then an axon conducts nerve signals away from the cell body. Myelin Sheath Many axons are covered by a protective myelin sheath. The myelin sheath develops when Schwann cells (PNS) or oligodendrocytes (CNS) wrap their membranes around an axon many times. Each neuroglia cell covers only a portion of an axon, so the myelin Page 282sheath is interrupted. The gaps where there is no myelin sheath are called nodes of Ranvier (Fig. 14.3). Later in this section, we will see how the myelin sheath plays an important role in the rate at which signals move through the neuron.

Answer 372

Science in your life: aspirin

Answer 373

1. More than 100 substances are known or suspected to be neurotransmitters. 2. Common: acetylcholine, norepinephrine, dopamine, serotonin, glutamate, and GABA (gamma aminobutyric acid). 3. transmit signals between nerves; Nerve-muscle, nerve-organ, and nerve-gland synapses also communicate using neurotransmitters. 4. **_Acetylcholine (ACh) and norepinephrine are active in both the CNS and PNS_**. * In the PNS, these neurotransmitters act at synapses called **_neuromuscular junctions_**. We will explore the structure of the neuromuscular junctions in Section 13.2. 1. In the PNS, ACh excites skeletal muscle but inhibits cardiac muscle. It has either an excitatory or inhibitory effect on smooth muscle or glands, depending on their location. * Norepinephrine generally excites smooth muscle. * In the CNS, norepinephrine is important to dreaming, waking, and mood. * Serotonin is involved in thermoregulation, sleeping, emotions, and perception. * Many drugs that affect the nervous system act at the synapse. Some interfere with the actions of neurotransmitters, and other drugs prolong the effects of neurotransmitters (see Section 14.5). 1.

Answer 374

14.3 Check Yourself

Answer 375

14.5 Drug Therapy and Drug Abuse LEARNING OUTCOMES Upon completion of this section, you should be able to Explain the ways that drugs interact with the nervous system. Classify drugs as to whether they have a depressant, stimulant, or psychoactive effect on the nervous system.

Answer 376

Range in shape from squamous to columnar, many are ciliated • They line the ventricles of the brain and central canal of the spinal cord to form a permeable barrier between cerebrospinal fluid (CSF) and tissue fluid bathing cells of CNS, as well as from blood • Functionally, ependymal cells produce, possibly monitor, and assist in the circulation of cerebrospinal fluid – Help circulate CNS with their cilia

Answer 377

Nerve Impulse Sodium Gates Open * Protein channels specific for sodium ions are located in the plasma membrane of the axon. * When an action potential begins in response to a threshold stimulus, these protein channels open and sodium ions rush into the cell. * Adding positively charged sodium ions causes the inside of the axon to become positive compared to the outside (Fig. 14.4c). T * his change is called depolarization, because the charge (polarity) inside the axon changes from negative to positive. * Potassium Gates Open * Almost immediately after depolarization, the channels for sodium close and a separate set of potassium protein channels opens. * Potassium flows rapidly from the cell. As positively charged potassium ions exit the cell, the inside of the cell becomes negative again because of the presence of large, negatively charged ions trapped inside the cell. This change in polarity is called repolarization, because the inside of the axon resumes a negative charge as potassium exits the axon (Fig. 14.4d). Finally, the sodium–potassium pump completes the action potential. Potassium ions are returned to the inside of the cell and sodium ions to the outside, and resting potential is restored. * Neural Transmission: Resting Membrane Potential and Propagation * Graph of an Action Potential * To visualize such rapid fluctuations in voltage across the axonal membrane, researchers generally find it useful to plot the voltage changes over time (Fig. 14.4e). During depolarization, the voltage increases from −70 mV to −55 mV to between +30 and +35 mV as sodium ions move to the inside of the axon. In repolarization, the opposite change occurs when potassium ions leave the axon. The entire process is very rapid, requiring only 3 to 4 milliseconds (ms) to complete.

Answer 378

**_The structures of neurons_** **_These are the three parts:_** The common parts See download, review and study: Page 282, (Fig. 14.3)

Answer 379

difference in electron potential inside and outside of axon of neuron across membrane about 40 ..., inside the axon is negative- resting potential- no impulse - structure of membrane- cell membranes channel proteins- neurons- 2 channels Na + or K+ channel- resting - Sodium is greater, outside than inside, and K is greater inside than outside 3 sodium out for every 2 K into the cell when nerve impulse or action potential reaches center of membrane- stiumuls causes membraine to depolarize- action potential- all or none event- if depolarize certain level- threshold- action potential occurs gates open first, potential begins, sodium float into axon- positive charge- once moved- membrane potental- -70 to +35, threshold- overcomes, all or nothing event- depolarization- sudden rush of sodium axons into- negative to positive, K- channels open- float down to oustide of axon- concentration gradient- also + = repolarization- resumes negative charge as potassium exits- travels down axon- one membrane at a time- depolarization- stiumulus to neighboring - sections of membrane refractory period- sodium gates- unpoen- action potential can't move backwards and always moves in same direction - K and Na pump- restores previous ion distribution Na outside and K inside- each small segment depolarization and repolarization takes just a few miliseconds, ready to transmit another action potential

Answer 380

Summarize the major regions of the brain and describe the general function of each. CONNECTING THE CONCEPTS For more information on the central nervous system, refer to the following discussions: Section 10.5 examines how the central nervous system controls breathing. Section 18.5 explores how aging and diseases such as Alzheimer disease influence the brain. Sections 23.3 and 23.4 outline how the size of the brain has changed over the course of human evolution.

Answer 381

The CNS performs information processing and integration, summing up the input it receives from all over the body. The CNS reviews the information, stores the information as memories, and creates the appropriate motor responses. The smell of those baking cookies evokes memories of their taste.

Answer 382

1. CNS, where **sensory information** is **received** and 2. **motor control is initiated.**

Answer 383

has been called the last great frontier of biology. The goal of modern neuroscience is to understand the structure and function of the brain’s various parts so well that it will be possible to prevent or correct the thousands of mental disorders that rob humans of a normal life. This section gives only a glimpse of what is known about the brain and the modern avenues of research. We discuss the parts of the brain with reference to the cerebrum, the diencephalon, the cerebellum, and the brain stem. The brain’s four ventricles (see Fig. 14.7) are called, in turn, the two lateral ventricles, the third ventricle, and the fourth ventricle. It may be helpful for you to associate the cerebrum with the two lateral ventricles, the diencephalon with the third ventricle, and the brain stem and cerebellum with the fourth ventricle (Fig. 14.9a). Figure 14.9 The human brain. a. The cerebrum is the largest part of the brain in humans. b. Viewed from above, the cerebrum has left and right cerebral hemispheres. The hemispheres are connected by the corpus callosum. (b): ©McGraw-Hill Education; photo and dissection by Christine Eckel

Answer 384

* Diencephalon * skull * meninges * pituitary gland * fourth ventricle * cord * Cerebrum * Diencephalon * Cerebellum * hypothalamus * midbrain * pons * Brain stem * a. Parts of brain * b. Cerebral hemispheres * lateral ventricle * third ventricle * pineal gland * corpus callosum * thalamus (surrounds the third ventricle) * medulla oblongata * Study! * * Figure 14.8 The human brain.

Answer 385

What happens to excess cerebrospinal fluid?

Answer 386

Important for Nervous SyStem

Answer 387

All or Nothing Action Potential In Figure 14.4b, the threshold voltage is around −55 mV.

Answer 388

resting neuron- charge difference between inside and outside, maintained by K and Na pumps- while other channels- sodium -- can't get back in- exterior net positive, net negative interior- resting membrane potential- nerve impulse begins when stiumulus disturbs on dendrite- Na ions float into cell- charge reduced, change is enough, will cause nearby Na channels to open- depolarize-d local region- positively charged on inside and negative on the outside- neighboring channels open- depolarization on membrane- action potential- changes occur - to restore resting membrane potential, Na closes, K opens- allows K to float out repolarization membrane

Answer 389

The synapse

Answer 390

* The tracts cross containing: 1. **_midbrain:_** * **relay station** for tracts between the cerebrum and the spinal cord or cerebellum. * **reflex centers** for visual, auditory, and tactile responses. 1. **_pons_**: * (“bridge” in Latin) * contains bundles of **axons** traveling * between the cerebellum and the rest of the CNS. * functions with the medulla oblongata to **regulate breathing rate.** * **Reflex centers** in the pons **coordinate head movements** in response to visual and auditory stimuli. 3. **medulla oblongata** * **reflex centers** for r*egulating heartbeat, breathing, and vasoconstriction (blood pressure).* * It also contains the reflex centers for *vomiting, coughing, sneezing, hiccuping, and swallowing.* * superior to the spinal cord * * groups of axons that travel together; * Between brain and higher level brain centers 1. **Ascending tracts** convey **sensory information.** 2. **Motor information** is transmitted on **descending tracts.**

Answer 391

These are the 14.2 learning goals.

Answer 392

Cerebellum (cont) Cerebral Hemispheres with the 4 \_\_\_\_\_\_\_\_\_\_\_\_\_

Answer 393

14.2 The Central Nervous System LEARNING OUTCOMES Upon completion of this section, you should be able to Identify the structures of the spinal cord and provide a function for each. Identify the structures of the brain and provide a function for each. Identify the lobes and major areas of the human brain. Distinguish between the functions of the primary motor and the primary somatosensory areas of the brain.

Answer 394

contains two types of cells: neurons and neuroglia (sometimes referred to as glial cells). Neurons are the cells that transmit nerve impulses between parts of the nervous system; neuroglia support and nourish neurons. Neuroglia (see Section 4.4) greatly outnumber neurons in the brain. There are several types of neuroglia in the CNS, each with specific functions. Microglia are phagocytic cells that help remove bacteria and debris, whereas astrocytes provide metabolic and structural support directly to the neurons. The myelin sheath is formed from the membranes of tightly spiraled neuroglia. In the PNS, Schwann cells perform this function, leaving gaps called nodes of Ranvier. In the CNS, neuroglia cells called oligodendrocytes form the myelin sheath. We will focus our attention on the anatomy and physiology of neurons.

Answer 395

1. Protein channels specific for sodium ions are located in the plasma membrane of the axon. When an action potential begins in response to a threshold stimulus, these protein channels open and **sodium ions rush into** the cell. 2. Adding positively charged sodium ions causes the inside of the axon to become positive compared to the outside (Fig. 14.4c). This change is called **depolarization**, because the charge (polarity) inside the axon changes from negative to positive. 3. Almost immediately after depolarization, the channels for sodium close and a separate set of **potassium protein channels opens**. **Potassium flows rapidly from the cell.** As positively charged potassium ions exit the cell, the inside of the cell becomes negative again because of the presence of large, negatively charged ions trapped inside the cell. This change in polarity is called **repolarization,** because the inside of the axon resumes a negative charge as potassium exits the axon 4. Finally, the **_sodium–potassium pump completes the action potential._** *Potassium ions are returned to the inside of the cell and sodium ions to the outside, and resting potential is restored.*

Answer 396

Association areas and Processing Centers Wernick's and Broca's aphasias

Answer 397

These are the central nervous system, and this is what is primarily done.

Answer 398

Drug Mode of Action As mentioned in Section 14.1, there are more than 100 known neurotransmitters. The most widely studied neurotransmitters to date are acetylcholine, norepinephrine, dopamine, serotonin, and gamma-aminobutyric acid (GABA). Acetylcholine is an essential CNS neurotransmitter for memory circuits in the limbic system. Norepinephrine is important to dreaming, waking, and mood. The neurotransmitter dopamine plays a central role in the brain’s regulation of mood. Dopamine is also the basal nuclei neurotransmitter that helps organize coordinated movements. Serotonin is involved in thermoregulation, sleeping, emotions, and perception. GABA is an abundant inhibitory neurotransmitter in the CNS.

Answer 399

14.5 Drug Therapy and Drug Abuse LEARNING OUTCOMES Upon completion of this section, you should be able to Explain the ways that drugs interact with the nervous system. Classify drugs as to whether they have a depressant, stimulant, or psychoactive effect on the nervous system. List the long-term effects of drug use on the body. As you are reading these words, synapses throughout your brain are organizing, integrating, and cataloging the information you take in. Neurotransmitters at these synapses control the firing of countless action potentials, thus creating a network of neural circuits. It is amazing to realize that all thoughts, feelings, and actions of a human are dependent on neurotransmitters in the CNS and PNS. By modifying or controlling synaptic transmission, a wide variety of drugs with neurological activity, both legal pharmaceuticals and illegal drugs of abuse, can alter mood, emotional state, behavior, and personality.

Answer 400

sensory, motor, interneurons... interneurons

Answer 401

14.2 The Central Nervous System LEARNING OUTCOMES Upon completion of this section, you should be able to Identify the structures of the spinal cord and provide a function for each. Identify the structures of the brain and provide a function for each. Identify the lobes and major areas of the human brain. Distinguish between the functions of the primary motor and the primary somatosensory areas of the brain. The spinal cord and the brain make up the CNS, where sensory information is received and motor control is initiated. Both the spinal cord and the brain are protected by bone. The spinal cord is surrounded by vertebrae, and the brain is enclosed by the skull. Also, both the spinal cord and the brain are wrapped in protective Page 287membranes known as meninges (sing., meninx). Meningitis is an infection of the meninges and may be caused by either bacterial or viral pathogens. The spaces between the meninges are filled with cerebrospinal fluid, which cushions and protects the CNS. In a spinal tap (lumbar puncture), a small amount of this fluid is withdrawn from around the spinal cord for laboratory testing. Cerebrospinal fluid is also contained within the ventricles of the brain and in the central canal of the spinal cord. The brain has four ventricles, interconnecting chambers that produce and serve as a reservoir for cerebrospinal fluid (Fig. 14.7). Normally, any excess cerebrospinal fluid drains away into the cardiovascular system. However, blockages can occur. In an infant, the brain can enlarge due to cerebrospinal fluid accumulation, resulting in a condition called hydrocephalus (“water on the brain”). If cerebrospinal fluid collects in an adult, the brain cannot enlarge. Instead, it is pushed against the skull. Such situations cause severe brain damage and can be fatal unless quickly corrected. Figure 14.7 The ventricles of the brain. The brain has four ventricles. A lateral ventricle is found on each side of the brain. They join at the third ventricle. The third ventricle connects with the fourth ventricle superiorly; the central canal of the spinal cord joins the fourth ventricle inferiorly. All structures are filled with cerebrospinal fluid. a. Lateral view of ventricles seen through a transparent brain. b. Anterior view of ventricles seen through a transparent brain. The CNS is composed of two types of nervous tissue—gray matter and white matter. Gray matter contains cell bodies and short, nonmyelinated axons. White matter contains myelinated axons that run together in bundles called tracts. The Spinal Cord The spinal cord extends from the base of the brain through a large opening in the skull called the foramen magnum (see Fig. 12.4). From the foramen magnum, the spinal cord proceeds inferiorly in the vertebral canal. Structure of the Spinal Cord A cross-section of the spinal cord (Fig. 14.8a) shows a central canal, gray matter, and white matter. Figure 14.8b shows how an individual vertebra protects the spinal cord. The spinal nerves project from the cord through small openings called intervertebral foramina. Fibrocartilage intervertebral discs separate the vertebrae. If a disc ruptures or herniates, it may compress a spinal nerve, resulting in pain and a loss of mobility. Figure 14.8 The organization of white and gray matter in the spinal cord and the spinal nerves. a. Cross-section of the spinal cord, showing arrangements of white and gray matter. b. Spinal nerves originating from the spinal cord. c. The spinal cord is protected by vertebrae. d. Spinal nerves emerging from the cord. (a): ©Scientifica/Corbis Documentary/Getty Images; (d): ©McGraw-Hill Education/Rebecca Gray, photographer & Don Kincaid, dissections The central canal of the spinal cord contains cerebrospinal fluid, as do the meninges that protect the spinal cord. The gray matter is centrally located and shaped like the letter H (Fig. 14.8a–c). Portions of sensory neurons and motor neurons are found in gray matter, as are interneurons that communicate with these two types of neurons. The dorsal root of a spinal nerve contains sensory fibers entering the gray matter. The ventral root of a spinal nerve contains motor fibers exiting the gray matter. The dorsal and ventral roots join before the spinal nerve leaves the vertebral canal (Fig. 14.8c, d), forming a mixed nerve. Spinal nerves are a part of the PNS. The white matter of the spinal cord occurs in areas around the gray matter. The white matter contains ascending tracts taking information to the brain (primarily located posteriorly) and descending tracts taking information from the brain (primarily located anteriorly). Many tracts cross just after they enter and exit the brain, so the left side of the brain controls the right side of the body. Likewise, the right side of the brain controls the left side of the body. Functions of the Spinal Cord The spinal cord provides a means of communication between the brain and the peripheral nerves that leave the cord. When someone touches your hand, sensory receptors generate nerve signals that pass through sensory fibers to the spinal cord and up ascending tracts to the brain (see Fig. 14.2b, red arrows). The gate control theory of pain proposes that the tracts in the spinal cord have “gates” and that these gates control the flow of pain messages from the peripheral nerves to the brain. Depending on how the gates process a pain signal, the pain message can be allowed to pass directly to the brain or can be prevented from reaching the brain. Pain messages may also be blocked by other inputs, such as those received from touch receptors or endorphins. The brain coordinates the voluntary control of our limbs. Motor signals originating in the brain pass down descending tracts to the spinal cord and out to our muscles by way of motor fibers (see Fig. 14.2b, black arrows). Therefore, if the spinal cord is severed, we suffer a loss of sensation and a loss of voluntary control—paralysis. If the cut occurs in the thoracic region, the lower body and legs are paralyzed, a condition known as paraplegia. If the injury is in the neck region, all four limbs are usually affected, a condition called quadriplegia. Page 288 Reflex Actions The spinal cord is the center for thousands of reflex arcs (see Fig. 14.17). A stimulus causes sensory receptors to generate signals that travel in sensory axons to the spinal cord. Interneurons integrate the incoming data and relay signals to motor neurons. A response to the stimulus occurs when motor axons cause skeletal muscles to contract. Motor neurons in a reflex arc may also affect smooth muscle, organs, or glands. Each interneuron in the spinal cord synapses with numerous other neurons. From there, interneurons send signals to other interneurons and motor neurons. Similarly, the spinal cord creates reflex arcs for the internal organs. For example, when blood pressure falls, internal receptors in the carotid arteries and aorta generate nerve signals that pass through sensory fibers to the cord and then up an ascending tract to a cardiovascular center in the brain. Thereafter, nerve signals pass down a descending tract to the spinal cord. Motor signals then cause blood vessels to constrict, so that the blood pressure rises. The Brain The human brain has been called the last great frontier of biology. The goal of modern neuroscience is to understand the structure and function of the brain’s various parts so well that it will be possible to prevent or correct the thousands of mental disorders that rob humans of a normal life. This section gives only a glimpse of what is known about the brain and the modern avenues of research. We discuss the parts of the brain with reference to the cerebrum, the diencephalon, the cerebellum, and the brain stem. The brain’s four ventricles (see Fig. 14.7) are called, in turn, the two lateral ventricles, the third ventricle, and the fourth ventricle. It may be helpful for you to associate the cerebrum with the two lateral ventricles, the diencephalon with the third ventricle, and the brain stem and cerebellum with the fourth ventricle (Fig. 14.9a). Figure 14.9 The human brain. a. The cerebrum is the largest part of the brain in humans. b. Viewed from above, the cerebrum has left and right cerebral hemispheres. The hemispheres are connected by the corpus callosum. (b): ©McGraw-Hill Education; photo and dissection by Christine Eckel The Cerebrum The cerebrum is the largest portion of the brain in mammals, including humans. The cerebrum is the last center to receive sensory input and carry out integration before commanding voluntary motor responses. It communicates with and coordinates the activities of the other parts of the brain. Cerebral Hemispheres Just as the human body has two halves, so does the cerebrum. These halves are called the left and right cerebral hemispheres (Fig. 14.9b). A deep groove called the longitudinal fissure divides the left and right cerebral hemispheres. The two cerebral hemispheres communicate via the corpus callosum, an extensive bridge of nerve tracts. Page 289The characteristic appearance of the cerebrum is the result of thick folds, called gyri (sing., gyrus) separated by shallow grooves called sulci (sing., sulcus). The sulci divide each hemisphere into lobes (Fig. 14.10). The frontal lobe is the most anterior of the lobes (directly behind the forehead). The parietal lobe is posterior to the frontal lobe. The occipital lobe is posterior to the parietal lobe (at the rear of the head). The temporal lobe lies inferior to the frontal and parietal lobes (at the temple and the ear). Figure 14.10 The lobes of the cerebral hemispheres. Each cerebral hemisphere is divided into four lobes: frontal, parietal, temporal, and occipital. Centers in the frontal lobe control movement and higher reasoning, as well as the smell sensation. Somatic sensing is carried out by parietal lobe neurons, and those of the temporal lobe receive sound information. Visual information is received and processed in the occipital lobe. The Cerebral Cortex The cerebral cortex is a thin, highly convoluted outer layer of gray matter that covers the cerebral hemispheres. Recall that gray matter consists of neurons whose axons are not myelinated. The cerebral cortex contains over 1 billion cell bodies and is the region of the brain that accounts for sensation, voluntary movement, and all the thought processes we associate with consciousness. Primary Motor and Sensory Areas of the Cortex The cerebral cortex contains motor areas and sensory areas, as well as association areas. The primary motor area is in the frontal lobe just anterior to (before) the central sulcus. Voluntary commands to skeletal muscles begin in the primary motor area, and each part of the body is controlled by a certain section (Fig. 14.11a). In this illustration, notice that large areas of the cerebral cortex are devoted to controlling structures that carry out very fine, precise movements. Thus, the muscles that control facial movements—swallowing, salivation, expression—take up an especially large portion of the primary motor area. Likewise, hand movements require tremendous accuracy. Together, these two structures command nearly two-thirds of the primary motor area.Page 290 Figure 14.11 The primary motor and primary somatosensory areas of the brain. a. The primary motor area (blue) is located in the frontal lobe, adjacent to (b) the primary somatosensory area in the parietal lobe. The primary taste area is colored pink. The size of each body region shown indicates the relative amount of cortex devoted to control of that body region. SCIENCE IN YOUR LIFE Why does a stroke on the right side of the brain cause weakness or paralysis on the left side of the body? Descending motor tracts (from the primary motor area) and ascending sensory tracts (from the primary somatosensory area) cross over in the spinal cord and medulla. Motor neurons in the right cerebral hemisphere control the left side of the body and vice versa because of crossing-over. Likewise, sensation from the left half of the body travels to the right cerebral hemisphere. Destruction of brain tissue by a stroke interferes with outgoing motor signals to the opposite side of the body, as well as incoming sensory information from that side. The primary somatosensory area is just posterior to the central sulcus in the parietal lobe. Sensory information from the skin and skeletal muscles arrives here, where each part of the body is sequentially represented (Fig. 14.11b). Like the primary motor cortex, large areas of the primary sensory cortex are dedicated to those body areas with acute sensation. Once again, the face and hands require the largest proportion of the sensory cortex. Page 291Reception areas for the other primary sensations—taste, vision, hearing, and smell—are located in other areas of the cerebral cortex (see Fig. 14.10). The primary taste area in the parietal lobe (pink) accounts for taste sensations. Visual information is received by the primary visual cortex (blue) in the occipital lobe. The primary auditory area in the temporal lobe (green) accepts information from our ears. Smell sensations travel to the primary olfactory area (yellow) found on the deep surface of the frontal lobe. Association Areas Association areas are places where integration occurs and where memories are stored. Anterior to the primary motor area is a premotor area. The premotor area organizes motor functions for skilled motor activities, such as walking and talking at the same time. Next, the primary motor area sends signals to the cerebellum, which integrates them. A momentary lack of oxygen during birth can damage the motor areas of the cerebral cortex, resulting in cerebral palsy, a condition characterized by a spastic weakness of the arms and legs. The somatosensory association area, located just posterior to the primary somatosensory area, processes and analyzes sensory information from the skin and muscles. The visual association area in the occipital lobe associates new visual information with stored visual memories. It might “decide,” for example, if we have seen a face, scene, or symbol before. The auditory association area in the temporal lobe performs the same functions with regard to sounds. Processing Centers Processing centers of the cortex receive information from the other association areas and perform higher-level analytical functions. The prefrontal area, an association area in the frontal lobe, receives information from the other association areas and uses this information to reason and plan our actions. Integration in this area accounts for our most cherished human abilities. Reasoning, critical thinking, and formulating appropriate behaviors are possible because of integration carried out in the prefrontal area. The unique ability of humans to speak is partially dependent on two processing centers found only in the left cerebral cortex. Wernicke’s area is located in the posterior part of the left temporal lobe. Broca’s area is located in the left frontal lobe. Broca’s area is just anterior to the portion of the primary motor area for speech musculature (lips, tongue, larynx, and so forth) (see Fig. 14.10). Wernicke’s area helps us understand both the written and the spoken word and sends the information to Broca’s area. Broca’s area adds grammatical refinements and directs the primary motor area to stimulate the appropriate muscles for speaking and writing. Central White Matter Much of the rest of the cerebrum is composed of white matter. Myelination occurs and white matter develops as a child grows. Progressive myelination enables the brain to grow in size and complexity. For example, as neurons become myelinated within tracts designed for language development, children become more capable of speech. Descending tracts from the primary motor area communicate with lower brain centers, and ascending tracts from lower brain centers send sensory information up to the primary somatosensory area. Tracts within the cerebrum also take information among the different sensory, motor, and association areas pictured in Figure 14.10. The corpus callosum contains tracts that join the two cerebral hemispheres. Basal Nuclei Though the majority of each cerebral hemisphere is composed of tracts, there are masses of gray matter deep within the white matter. These basal nuclei integrate motor commands to ensure that the proper muscle groups are stimulated or inhibited. Integration ensures that movements are coordinated and smooth. Parkinson disease (see Section 18.5) is believed to be caused by degeneration of specific neurons in the basal nuclei. The Diencephalon The hypothalamus and thalamus are in the diencephalon, a region that encircles the third ventricle. The hypothalamus forms the floor of the third ventricle. The hypothalamus is an integrating center that helps maintain homeostasis. It regulates hunger, sleep, thirst, body temperature, and water balance. The hypothalamus controls the pituitary gland and thereby serves as a link between the nervous and endocrine systems. The thalamus consists of two masses of gray matter located in the sides and roof of the third ventricle. The thalamus is on the receiving end for all sensory input except the sense of smell. Visual, auditory, and somatosensory information arrives at the thalamus via the cranial nerves and tracts from the spinal cord. The thalamus integrates this information and sends it on to the appropriate portions of the cerebrum. The thalamus is involved in arousal of the cerebrum, and it participates in higher mental functions, such as memory and emotions. The pineal gland, which secretes the hormone melatonin, is located in the diencephalon. Presently, there is much popular interest in the role of melatonin in our daily rhythms. Some researchers believe it can help alleviate jet lag or insomnia. Scientists are also interested in the possibility that the hormone may regulate the onset of puberty. The Cerebellum The cerebellum lies under the occipital lobe of the cerebrum and is separated from the brain stem by the fourth ventricle. The cerebellum has two portions joined by a narrow median portion. Each portion is primarily composed of white matter. In a longitudinal section, the white matter has a treelike pattern called arbor vitae. Overlying the white matter is a thin layer of gray matter that forms a series of complex folds. The cerebellum receives sensory input from the eyes, ears, joints, and muscles about the present position of body parts. It also receives motor output from the cerebral cortex about where these parts should be located. After integrating this information, the cerebellum sends motor signals by way of the brain stem to the skeletal muscles. In this way, the cerebellum maintains posture and balance. It also ensures that all the muscles work together to produce smooth, coordinated, voluntary movements. The cerebellum assists in the learning of new motor skills, such as playing the piano or hitting a baseball. The Brain Stem The tracts cross in the brain stem, which contains the midbrain, the pons, and the medulla oblongata (see Fig. 14.9a). The midbrain acts as a relay station for tracts passing between the cerebrum and Page 292the spinal cord or cerebellum. It also has reflex centers for visual, auditory, and tactile responses. The pons (“bridge” in Latin) contains bundles of axons traveling between the cerebellum and the rest of the CNS. In addition, the pons functions with the medulla oblongata to regulate breathing rate. Reflex centers in the pons coordinate head movements in response to visual and auditory stimuli. The medulla oblongata contains a number of reflex centers for regulating heartbeat, breathing, and vasoconstriction (blood pressure). It also contains the reflex centers for vomiting, coughing, sneezing, hiccuping, and swallowing. The medulla oblongata lies just superior to the spinal cord, and it contains tracts that ascend or descend between the spinal cord and higher brain centers. Recall that tracts are groups of axons that travel together. Ascending tracts convey sensory information. Motor information is transmitted on descending tracts. The Reticular Formation The reticular formation is a complex network of nuclei, which are masses of gray matter, and fibers that extends the length of the brain stem (Fig. 14.12). The reticular formation is a major component of the reticular activating system (RAS). The RAS receives sensory signals and sends them to higher centers. Motor signals received by the RAS are sent to the spinal cord. Figure 14.12 The reticular formation of the brain. The reticular formation receives and sends on motor and sensory information to various parts of the CNS. One portion, the reticular activating system (RAS) (see arrows), arouses the cerebrum and, in this way, controls alertness versus sleep. The RAS arouses the cerebrum via the thalamus and causes a person to be alert. If you want to awaken the RAS, surprise it with sudden stimuli, such as an alarm clock ringing, bright lights, smelling salts, or cold water splashed on your face. The RAS can filter out unnecessary sensory stimuli, explaining why you can study with the TV on. Similarly, the RAS allows you to take a test without noticing the sounds of the people around you—unless the sounds are particularly distracting. To inactivate the RAS, remove visual or auditory stimuli, allowing yourself to become drowsy and drop off to sleep. General anesthetics function by artificially suppressing the RAS. A severe injury to the RAS can cause a person to become comatose, from which recovery may be impossible. CHECK YOUR PROGRESS 14.2 List the functions of the spinal cord. Answer Provides a means of communication between the brain and the peripheral nerves, and is the center for reflex actions. Summarize the major regions of the brain and describe the general function of each. Answer Cerebrum—largest part of the brain, integrates sensory inputs and coordinates the activities of the other parts of the brain; diencephalon—contains the hypothalamus and thalamus, maintains homeostasis, receives sensory input; cerebellum—sends out motor impulses by way of the brain stem to the skeletal muscles, produces smooth, coordinated voluntary movements; brain stem—contains the midbrain, pons, and medulla oblongata, acts as a relay station, and the medulla has reflex centers. Relate how the RAS aids in homeostasis. Answer The RAS regulates a person’s alertness, relays sensory signals to higher centers, and filters out unnecessary stimuli, which are important functions in being properly responsive to one’s environment. CONNECTING THE CONCEPTS For more information on the central nervous system, refer to the following discussions: Section 10.5 examines how the central nervous system controls breathing. Section 18.5 explores how aging and diseases such as Alzheimer disease influence the brain. Sections 23.3 and 23.4 outline how the size of the brain has changed over the course of human evolution.

Nervous System Flashcards

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