Lecture Exam #3 Flashcards

Question

Compare and contrast short-term and long-term memory and describe the parts of the brain involved with each

Answer 1

Short-term memory (STM) is generally characterized by limited capacity (approximately seven small segments of information) and brief duration (typically lasting less than 1 minute unless the information is rehearsed). Once information is placed into long-term memory (LTM), it may exist for limitless periods of time. So, for example, if over the weekend you practice retrieving the information from lecture and/or work with a study partner to explain a lecture concept, you likely will store the information as LTM within the cerebral lobes. Conversion from STM to LTM is called encoding, or memory consolidation. Encoding requires the proper functioning of two components of the limbic system: the hippocampus and the amygdaloid body. The hippocampus is required for the formation of STM, whereas LTM is stored primarily in the corresponding association areas of the cerebral cortex. For example, voluntary motor activity memory is stored in the premotor cortex, whereas memory of sounds is stored in the auditory association area. Because STM and LTM involve different anatomic structures, loss of the ability to form STM does not affect the maintenance or accessibility of LTM.

Answer 2

Expression of our emotions is interpreted by our limbic system but ultimately is controlled by the prefrontal cortex. Irrespective of how we feel, this cortical region decides the appropriate way to show our feelings. Researchers have learned that many important aspects of emotion also depend upon an intact, functional amygdaloid body and hippocampus (components of the limbic system). If specific regions of either of these structures are damaged or artificially stimulated, we exhibit either deadened or exaggerated expressions of aggression, affection, anger, fear, love, pain, pleasure, or sexuality, as well as anomalies in learning and memory.

Answer 3

CN I Olfactory Nerve Sensory nerve for olfaction (smell) CN II Optic Nerve Sensory nerve for vision CN III Oculomotor Nerve Motor nerve that controls muscles that move eye, lift eyelid, change pupil diameter, change lens shape CN IV Trochlear Nerve Motor nerve that controls superior oblique eye muscle CN V Trigeminal Nerve Mixed nerve that receives somatic sensation from face; controls muscles involved in chewing CN VI Abducens Nerve Motor nerve that controls lateral rectus muscle that abducts eye

Answer 4

CN VII Facial Nerve Mixed nerve that controls muscles of facial expression and conducts taste sensations from tongue CN VIII Vestibulocochlear Nerve Sensory nerve involved in hearing and equilibrium CN IX Glossopharyngeal Nerve Mixed nerve that receives taste and touch from tongue; motor control of pharynx muscle CN X Vagus Nerve Mixed nerve that controls muscles in pharynx and larynx; conducts sensation from many viscera; major source of parasympathetic output CN XI Accessory Nerve Motor nerve that controls muscles of neck, pharynx CN XII Hypoglossal Nerve Motor nerve that controls tongue muscles

Answer 5

Their first function is to provide an essential structural and functional link between the brain and the torso and limbs of the body. Sensory input is relayed from the torso and limbs to the brain, and motor output is relayed from the brain to the torso and limbs. These vital inputs and outputs are relayed along neuron pathways that are within the spinal cord and spinal nerves. Notice that both sensory input and motor output are relayed along the pathways within the spinal cord and spinal nerves. The second important function of the spinal cord and spinal nerves is their role in spinal reflexes. These involve nervous system responses that do not require the involvement of the brain, but instead have the spinal cord as the integration center. Spinal reflexes initiate our quickest reactions to a stimulus. It is through spinal reflexes that the spinal cord exhibits some functional independence from the brain.

Answer 6

sensory input is relayed from receptors within torso and limbs to the brain motor output is relayed from brain to effectors, or the muscles and glands of the torso and limbs. This information is relayed along various neural pathways

Answer 7

White matter is (1) primarily composed of myelinated axons and (2) functioning to relay nerve signals. The white matter of the spinal cord is external to the gray matter and on each side of the cord is partitioned into three distinct anatomic structural regions based upon their location within the spinal cord. Each of these regions is called a funiculus. Each posterior funiculus is white matter that lies between the posterior gray horns on the posterior side of the cord and the posterior median sulcus. The lateral funiculus is the white matter on each lateral side of the spinal cord. The anterior funiculus is composed of white matter that occupies the space on each anterior side of the cord between anterior gray horns and the anterior median fissure; the anterior funiculi are interconnected by the white commissure. The axons within each funiculus are organized into smaller structural units (or bundles of myelinated axons) called fasciculi.

Answer 8

White matter on each side of the cord can also be referred to as tracts, which have common functions. Individual tracts are either (1) sensory (or ascending) tracts, which conduct nerve signals from the spinal cord to the brain, or (2) motor (or descending) tracts, which conduct nerve signals from the brain to the spinal cord.

Answer 9

Sensory pathways include the sensory neurons that relay sensory input to the brain. Sensory pathways are also called ascending pathways because the nerve signals are relayed from the sensory receptors superiorly to the brain. Motor pathways include the series of motor neurons that relay motor output from the brain. Motor pathways are also called descending pathways because the nerve signals are relayed from the brain inferiorly to the body’s muscles and glands.

Answer 10

Most conduction pathways—whether sensory or motor—share several general characteristics: Paired tracts. All pathways are composed of paired tracts. Thus, a pathway on one side of the CNS has a matching tract on the other side of the CNS. Composed of two or more neurons. Most pathways are composed of a series of two or three neurons that form the pathway. Common location of neuron cell bodies. Neuron cell bodies are located in one of three general places: the posterior root ganglion, the gray horns within the spinal cord, or nuclei within the brain along the pathway. Common location of axons. The axons of the different neurons extend through spinal nerves, the spinal cord (as named tracts or fasciculi), and the brain. Decussation. Most pathways include neurons that cross over, or decussate, from one side of the body to the other side at some point along the pathway—within either the spinal cord or the brain. This means that the left side of the brain receives sensory input from or initiates motor output to the right side of the body, whereas the right side of the brain receives sensory input from or initiates motor output to the left side of the body. The term contralateral is used to indicate the relationship to the opposite side. Over 90% of all neurons within pathways decussate. Limited ipsilateral pathway. Pathways may have some neurons (about 10%) that remain on the same side of the body. The term ipsilateral is used to indicate the relationship to the same side.

Answer 11

General sense receptors are sensory receptors located throughout the body. General sense receptors are subdivided into two categories: somatic sensory (or somatosensory) receptors and visceral sensory receptors. Somatic sensory (or somatosensory) receptors are tactile receptors or proprioceptors. Tactile receptors are housed within both the skin and mucous membranes that line body cavities. These sensory receptors monitor characteristics of an object (e.g., texture). Proprioceptors are located within joints, muscles, and tendons to detect stretch and pressure relative to position and movement of the skeleton and skeletal muscles. Visceral sensory receptors are located in the walls of the viscera (internal organs) and blood vessels. They detect changes to an organ or a blood vessel (e.g., stretch).

Answer 12

Sensory pathways use a series of two or three neurons to transmit nerve signals from the sensory receptors to the brain, which are the primary neuron, secondary neuron, and tertiary neuron. ∙ The primary neuron is the first neuron in the chain of neurons. The primary neuron extends from the sensory receptor to the CNS (brain or spinal cord), where it synapses with a secondary neuron. ∙ The secondary neuron is an interneuron that extends from the primary neuron to either the tertiary neuron or the cerebellum. ∙ The tertiary neuron is also an interneuron. It extends from the secondary neuron to the cerebrum (specifically, the primary somatosensory cortex of the parietal lobe). Pathways that lead to the cerebellum do not have a tertiary neuron.

Answer 13

The anterolateral pathway (or spinothalamic pathway) uses a chain of three neurons to communicate with the brain about a specific stimulus. This pathway originates at tactile somatosensory receptors within both the skin and mucous membranes. This sensory input is providing information to the brain (specifically, the cerebral cortex) about crude touch and pressure as well as pain and temperature. The posterior funiculus–medial lemniscal pathway uses a chain of three sensory neurons to communicate with the brain about a specific stimulus. This pathway originates at either of the two types of somatosensory receptors: (1) tactile receptors housed within both the skin and mucous membranes or (2) proprioceptors within joints, muscles, and tendons. This sensory input is providing information to the brain (specifically, the cerebral cortex) about discriminative touch, precise pressure, and vibration sensations from the tactile receptors of the skin and with conscious perception of the skeleton and skeletal muscles from proprioceptors. The spinocerebellar pathway uses a chain of only two neurons to communicate with the brain about a specific stimulus. This pathway originates at proprioceptors within joints, muscles, and tendons at different locations in the body. This sensory input is providing information to the brain (specifically, the cerebellum) related to subconscious postural input, which helps in maintaining balance

Answer 14

An upper motor neuron is the first neuron in a chain of neurons. The cell body of the upper motor neuron is housed within the cerebral cortex, cerebral nuclei, or a specific nucleus within the brainstem. Axons of the upper motor neuron synapse either directly upon lower motor neurons (in direct pathways) or upon interneurons that ultimately synapse upon lower motor neurons (in indirect pathways). The upper motor neurons either excite or inhibit the activity of lower motor neurons. ∙ The lower motor neuron is the last neuron in the chain of neurons. The cell body of a lower motor neuron is housed within the anterior horn of the spinal cord. Axons of the lower motor neurons exit the spinal cord through the anterior root and project to and innervate a specific skeletal muscle. The lower motor neuron always excites the skeletal muscle fibers to contract.

Answer 15

DIRECT PATHWAY houses Corticobulbar tracts: Voluntary movement of cranial and facial muscles Lateral corticospinal tracts: Voluntary movement of appendicular muscles Anterior corticospinal tracts: Voluntary movement of axial muscles INDIRECT PATHWAY houses Lateral Pathway: Rubrospinal tract: Regulates and controls precise discrete movements and tone in flexor muscles of the limbs Medial Pathway: Reticulospinal tract: Controls reflexive movements related to posture and maintaining balance Tectospinal tract: Regulates reflexive positional changes of the upper limbs, eyes, head, and neck due to visual and auditory stimuli Vestibulospinal tract: Regulates reflexive muscular activity that helps maintain balance during sitting, standing, and walking

Answer 16

Reflexes are rapid, preprogrammed, involuntary responses of muscles or glands to a stimulus. All reflexes have similar properties: ∙ A stimulus is required to initiate a reflex. ∙ A rapid response requires that few neurons are involved and synaptic delay is minimal. ∙ A preprogrammed response occurs the same way every time. ∙ An involuntary response requires no conscious intent or preawareness of the reflex activity. Thus, reflexes are usually not suppressed.

Answer 17

A reflex is a survival mechanism; it allows us to quickly respond to a stimulus that may be detrimental to our well-being without having to wait for the brain to process the information. Awareness of the stimulus occurs after the reflex action has been completed, in time to correct or avoid a potentially dangerous situation. (This is possible because sensory input has reached the cerebral cortex.)

Answer 18

1 A stimulus activates a sensory receptor. A sensory receptor (dendritic endings of a sensory neuron or specialized receptor cells) responds to external and internal stimuli, such as temperature, pressure, or tactile changes. Proprioceptors are sensory receptors found in muscles and tendons, and a stimulus to a proprioceptor (such as the tapping of tendon) may initiate a reflex as well. 2 The sensory neuron transmits a nerve signal to the CNS. A sensory neuron transmits a nerve signal from the receptor to the spinal cord (or brain). 3 Information from the nerve signal is processed in the integration center by interneurons. 4 The motor neuron transmits a nerve signal from the CNS to an effector. A motor neuron transmits a nerve signal from the CNS to a peripheral effector organ—a gland or a muscle. 5 The effector responds to the nerve signal from the motor neuron. An effector is a muscle or a gland that responds to the nerve signal from the motor neuron. This response is intended to counteract or remove the original stimulus.

Answer 19

Spinal reflex or cranial reflex. A reflex may be identified by the specific area of the central nervous system (integration center) that serves as the processing site. Spinal reflexes involve the spinal cord, whereas cranial reflexes involve the brain. ∙ Somatic reflex or visceral reflex. This classification criterion is determined by the type of effector that is stimulated by the motor neurons involved in the reflex. Somatic reflexes involve skeletal muscle as the effector. Visceral (or autonomic) reflexes involve cardiac muscle, smooth muscle, or a gland as the effector. ∙ Monosynaptic reflex or polysynaptic reflex. A reflex may also be classified by the number of neurons participating in the reflex. A monosynaptic reflex has only a sensory neuron and a motor neuron. The axon of the sensory neuron synapses directly on the motor neuron, whose axon projects to the effector. Thus, there is only one synapse between neurons. Ipsilateral reflex or contralateral reflex. The reflex may also be classified based upon whether it involves only one side of the body. An ipsilateral reflex is a reflex in which both the receptor and effector organs are on the same side of the spinal cord. A contralateral reflex is a reflex that involves an effector on the opposite side of the body from the receptor that detected the stimulus. Note that this terminology is only applicable to reflexes that involve the limbs. Innate reflex or acquired reflex. The reflex may be classified based upon whether you are born with it.

Answer 20

A stretch reflex is a simple monosynaptic reflex. A stretching force detected by a muscle spindle results in the contraction of that muscle. Conversely, antagonistic muscle contraction is dampened, in a process called reciprocal inhibition. A Golgi tendon reflex is a polysynaptic reflex. A contraction force detected by a Golgi tendon organ (within the tendon of the muscle) results in relaxation of that muscle. Conversely, antagonistic muscles are stimulated to contract, a process called reciprocal activation. A withdrawal reflex is a polysynaptic reflex that is initiated by a painful stimulus. The crossed-extensor reflex occurs in response to the withdrawal reflex, by stimulating the extensor muscles in the opposite limb and thereby ensuring the opposite limb supports the body’s weight.

Answer 21

Similarities: Sensory & Motor components Differences: SNS: Detect stimuli and transmission of nerve signals from the special senses, skin, & proprioreceptors to the CNS. Ex. Taste dinner, see mountains, or smell a babies skin. ANS: functions below the conscious level. Detect stimuli associated with blood vessels & internal organs. Initiate and transmit nerve signals from the CNS to cardiac, smooth muscle, and glands. Ex. Monitor carbon dioxide concentration in the blood

Answer 22

Somatic Nervous System Number of neurons in pathway One neuron from CNS: Somatic motor neuron axon extends from CNS to effector Axon properties Myelinated and thicker in diameter; fast nerve signal propagation Neurotransmitter released Acetylcholine (ACh) Response of effector Excitation only Ganglia associated with motor neurons: None Autonomic Nervous Systems Number of neurons: Two neurons from CNS: Preganglionic neuron has preganglionic axon that projects to ganglionic neuron; ganglionic neuron has postganglionic axon that projects to effector Axon properties Preganglionic axons are myelinated and small in diameter Postganglionic axons are unmyelinated and smaller in diameter; both have relatively slow nerve signal propagation Neurotransmitter released Preganglionic axons release ACh Postganglionic axons release either ACh or norepinephrine (NE) Response of effector Either excitation or inhibition Ganglia associated Parasympathetic division: terminal ganglia, intramural ganglia Sympathetic division: sympathetic trunk ganglia, prevertebral ganglia

Answer 23

The autonomic nervous system employs a chain of two lower motor neurons, a preganglionic neuron and a ganglionic neuron. The dendrites and cell body of a preganglionic neuron are housed within the CNS (brain or spinal cord). The preganglionic axon synapses with a ganglionic neuron within an autonomic ganglion. The postganglionic axon extends to an effector organ, which includes cardiac muscle, smooth muscle, and glands.

Answer 24

Autonomic function is regulated by three CNS regions: the hypothalamus, brainstem, and spinal cord. These CNS regions may be influenced by the cerebrum, thalamus, and limbic system. Hypothalamus: Integration and command center for autonomic functions; involved in emotions Brainstem: Contains major ANS reflex centers Spinal Cord: Contains ANS reflex centers for defecation and urination

Answer 25

The parasympathetic division functions to maintain homeostasis when we are at rest. This division is primarily concerned with conserving energy and replenishing nutrient stores. Because it is most active when the body is at rest or digesting a meal, the parasympathetic division has been nicknamed the rest-and-digest division. The sympathetic division functions to maintain homeostasis during exercise or times of stress or emergency, which includes the release of nutrients from stores (e.g., glucose released from the liver). Because of its function in regulating the more active states, the sympathetic division has been nicknamed the fight-or-flight division. (three Es: exercise, excitement, or emergency.)

Answer 26

One of the major differences is where the preganglionic neuron cell bodies are housed in the CNS. Parasympathetic preganglionic cell bodies are located in either the brainstem or the lateral gray matter of the S2–S4 spinal cord segments, and for this reason this division is also termed the craniosacral division. In comparison, sympathetic preganglionic neuron cell bodies are located in the lateral horns of the T1–L2 spinal cord segments, and so this division also goes by the phrase the thoracolumbar division. Other anatomic differences between the parasympathetic and sympathetic nervous system include: ∙ Length of preganglionic and postganglionic axons. Parasympathetic preganglionic axons are longer, and postganglionic axons are shorter, when compared to their counterparts in the sympathetic division. In the sympathetic division, preganglionic axons are shorter and postganglionic axons are longer. ∙ Number of preganglionic axon branches. Parasympathetic preganglionic axons tend to have few (less than 4) branches, whereas sympathetic preganglionic axons tend to have many branches (more than 20). Location of ganglia. Parasympathetic autonomic ganglia are either close to or within the effector (terminal ganglia and intramural ganglia, respectively). In comparison, sympathetic autonomic ganglia are relatively close to the spinal cord, and are on either side of the spinal cord or anterior to the spinal cord (sympathetic trunk ganglia and prevertebral ganglia, respectively).

Answer 27

It is the combination of long preganglionic axons with limited branches that results in a local response when the parasympathetic division is activated. Parasympathetic activity regulates either one or only a few structures at the same time without having to “turn on” or “turn off” all the other organs. In comparison, the combination of short preganglionic axons with more extensive branching within the sympathetic division allows for significant neuronal divergence and facilitates the activation of many structures simultaneously, a process called mass activation. This process is facilitated when the adrenal medulla is stimulated by the sympathetic division, which causes this gland to release norepinephrine and epinephrine into the blood. Mass activation is especially important in response to stress, when it is necessary to coordinate rapid changes in activity with numerous structures at once.

Answer 28

The cranial nerves containing neurons from the parasympathetic division are the oculomotor (CN III), facial (CN VII), glossopharyngeal (CN IX), and vagus (CN X) nerves. he first three of these nerves transmit parasympathetic innervation to the head, whereas the vagus nerve is the source of parasympathetic innervation for the thoracic and most abdominal organs. The oculomotor nerve (CN III) innervates both (1) the ciliary muscle (within the eye) to adjust the shape of the lens to see close-up objects and (2) the sphincter pupillae muscle of the iris (which constricts the pupil) to allow less light into the eye, such as when we first walk outside on a bright, sunny day The facial nerve (CN VII) innervates the submandibular and sublingual salivary glands in the floor of the mouth, lacrimal glands in the superior portion of each orbit, and small glands of the nasal cavity, oral cavity, and palate. Stimulation by the parasympathetic division increases release of secretion by these glands. Your mouth waters when you smell an aromatic meal due in part to these parasympathetic neurons within the facial nerve. The glossopharyngeal nerve (CN IX) innervates the parotid salivary glands and stimulates these glands to increase the release of their secretions. The axons of the preganglionic neurons extend from cell bodies within the brainstem to the otic ganglion, which is anterior to the ear. Postganglionic axons project from this ganglion to innervate the parotid salivary glands The vagus nerve (CN X) innervates the thoracic organs and most of the abdominal organs, as well as the gonads (ovaries and testes). The influence of the vagus nerve is extensive, given the significant number of autonomic effectors this cranial nerve innervates.

Answer 29

These preganglionic axons extend through the anterior root and then branch to form the pelvic splanchnic nerves, which contribute to a superior and inferior hypogastric plexus on each side of the body. The preganglionic axons that continue through each plexus project to the ganglionic neurons within either the terminal or intramural ganglia. The postganglionic axons extend to the effector. The target organs innervated include the distal portion of the large intestine, the rectum, the urinary bladder, the distal part of the ureter, and most of the reproductive organs. The parasympathetic regulation of these target organs causes increased smooth muscle motility (muscle contraction) and secretory activity in these portions of the digestive tract, contraction of smooth muscle in the urinary bladder wall and relaxation of the smooth muscle of the internal urethral sphincter, and erection of the female clitoris and the male penis.

Answer 30

The sympathetic pre-ganglionic neuron cell bodies are housed in the lateral horn of the T1–L2 regions of the spinal cord. From there, the preganglionic sympathetic axons travel with somatic motor axons to exit the spinal cord through first the anterior roots and then the T1–L2 spinal nerves.

Answer 31

Immediately lateral to the vertebral column and anterior to the paired spinal nerves are the left and right sympathetic trunks. A sympathetic trunk looks much like a pearl necklace. The “string” of the necklace is composed of bundles of axons, whereas the “pearls” are the sympathetic trunk ganglia (also known as paravertebral or sympathetic chain ganglia), which house sympathetic ganglionic neuron cell bodies.

Answer 32

Each type of pathway is dependent upon the location of the effector organ being innervated. Axons exit the sympathetic trunk by one of four pathways. The spinal nerve pathway extends from the spinal cord to effectors of the skin of the neck, torso, and limbs. Skin effectors include sweat glands, smooth muscle forming arrector pili muscles (which produce “goose bumps”), and smooth muscle cells within the walls of blood vessels. In this pathway, a preganglionic neuron synapses with a ganglionic neuron in a sympathetic trunk ganglion at either the same or different level The postganglionic sympathetic nerve pathway extends from the spinal cord to the internal organs of the thoracic cavity (including the esophagus, heart, lungs, and thoracic blood vessels), the effectors of the skin of the head (sweat glands, arrector pili, and blood vessels of the skin), the neck viscera, and the superior tarsal and dilator pupillae muscles in the eye The splanchnic nerve pathway extends from the spinal cord to the abdominal and pelvic organs (e.g., stomach, small intestines, kidney). In this pathway, a preganglionic neuron does not synapse with a ganglionic neuron in a sympathetic trunk ganglion. The final pathway is the adrenal medulla pathway. The internal region of the adrenal gland, called the adrenal medulla, is directly innervated by preganglionic sympathetic axons.

Answer 33

Due to the stimulation of the sympathetic division, you would experience increased respiratory rate, increased peripheral vasoconstriction and elevation of blood pressure, increased heart rate and force of contraction, and an increased rate of glucose release into the bloodstream.

Answer 34

Autonomic plexuses are collections of sympathetic postganglionic axons and parasympathetic preganglionic axons, as well as some visceral sensory axons. These sympathetic and parasympathetic axons are close to one another, but they do not interact with each another. Although these plexuses look like disorganized masses of axons, they provide a complex innervation pattern to their target organs. Autonomic plexuses are located in both the thoracic and abdominopelvic cavities. The cardiac, pulmonary, and esophageal plexuses are in the thoracic cavity. The abdominal aortic plexus consists of the celiac plexus, superior mesenteric plexus, and inferior mesenteric plexus.

Answer 35

The enteric nervous system (ENS) is an array of neurons (both autonomic motor and visceral sensory) that are arranged throughout the wall of the gastrointestinal (GI) tract, from the esophagus to the anus. The ENS not only innervates the smooth muscle and glands of the GI tract but also mediates the complex coordinated reflexes for peristalsis, or movement of materials through the GI tract. ENS neurons are located both within numerous small ganglia throughout the GI tract wall and within two large plexuses: (1) the submucosal plexus (also called the Meissner plexus) and (2) the myenteric plexus (also called the Auerbach plexus)

Answer 36

In the parasympathetic pathway, both the preganglionic and postganglionic axons release acetylcholine (ACh). In the sympathetic pathways, all preganglionic axons and a few specific postganglionic axons release ACh. Most postganglionic sympathetic axons release norepinephrine (NE). Neurons that synthesize and release acetylcholine (ACh) are called cholinergic neurons. Receptors that bind ACh are called cholinergic receptors. Neurons that synthesize and secrete norepinephrine (NE) are called adrenergic neurons. Most other sympathetic ganglionic neurons are adrenergic. Receptors that bind NE (or a related molecule, like epinephrine) are called adrenergic receptors.

Answer 37

The parasympathetic and sympathetic divisions both continuously release neurotransmitter to regulate specific target organs for either sustained stimulation or inhibition, a process referred to as the autonomic tone. Activity of an organ may be controlled merely by the change in tone within a single ANS division. autonomic tone is the background rate of activity of the ANS -it is the balance between the sympathetic and parasympathetic tone -parasympathetic tone maintains smooth muscle tone in the intestines and holds resting heart rate down to about 70-80 beats/minute -if the parasympathetic Vagus nerves to the heart are cut the heart beats as its own intrinsic rate of about 100 beats/minute -sympathetic tone keeps most blood vessels partially constricted and this maintains BP; loss of sympathetic tone can cause such a rapid drop in BP that a person goes into shock

Answer 38

Many effectors of the ANS have dual innervation, meaning that they are innervated by postganglionic axons from both parasympathetic and sympathetic divisions. The actions caused by activities of both the divisions on the same organ usually result in effects that are antagonistic or cooperative.

Answer 39

the neurosecretory cells of the adrenal medulla also are innervated only by the sympathetic division. In addition, many blood vessels are innervated by sympathetic axons only. Increased sympathetic stimulation increases smooth muscle contraction, resulting in increased blood pressure. Decreasing the sympathetic stimulation below the autonomic tone will result in vasodilation, just as lifting your foot off the gas pedal may slow a car down (because you are not supplying the gas). Thus, opposing effects are achieved merely by increasing or decreasing the auto- nomic tone in the sympathetic division. Other examples of innervation by only the sympathetic division are seen in sweat glands in the trunk (stimulates sweating) and innervation of arrector pili muscles in the skin to cause “goose bumps”

Answer 40

Cardiovascular reflex. A classic autonomic reflex involves the reduction of blood pressure. When blood pressure elevates, stretch receptors in the walls of large blood vessels are stimulated and nerve signals are propagated along visceral sensory neurons to the cardiac center in the medulla oblongata. These nerve signals inhibit sympathetic output and activate parasympathetic output to the heart to slow heart rate and decrease the volume of blood ejected, resulting in a decrease in blood pressure. ∙ Gastrointestinal reflex. Autonomic reflexes control defecation. Fecal matter entering the rectum causes stretch of the rectal wall. Sensory neurons relay increased nerve signals to the spinal cord, which initiates a change in nerve signals along motor neurons to the rectum and anal sphincter. ∙ Micturition reflex. The mechanism leading to bladder emptying is similar to that for fecal emptying of the colon. In a young child who is not yet toilet trained, stretch receptors send nerve signals to the sacral spinal cord when urine fills the bladder. The reflex results in contraction of the smooth muscle in the bladder wall and relaxation of the urinary sphincters.

Answer 41

The original energy form detected is specific to the type of sensory receptor (e.g., light energy is detect- ed by the eye, sound energy by the ear, and mechanical energy by blood vessels). However, the form the energy is transduced, or changed, to is always electrical energy, and it is sent along a sensory neuron. This sensory information is propagated as nerve signals to the CNS for interpretation. It is because sensory receptors transduce stimulus energy to electrical energy that sensory receptors are referred to as transducers

Answer 42

A receptive field is the area within which the dendritic endings of a single sensory neuron are distributed. The concept of a receptive field and its significance is most clearly shown with a comparison of receptive fields within the skin. Note the relative amount of area that sensory neurons of the skin are distributed in two different regions of the body—the skin of the fingertips and the skin of the upper back. The size of the receptive field will determine the ability of the CNS to identify the exact location of a stimulus. A small receptive field provides us with the ability to identify the stimulus location more specifically.

Answer 43

These characteristics include its modality, location, intensity, and duration. The modality or form of a stimulus is provided by a given type of sensory receptor relaying sensory input along designated sensory neurons to specific regions of the CNS.

Answer 44

Three criteria are used to categorize sensory receptors—receptor distribution, stimulus origin, and modality of stimulus.

Answer 45

The eyes, for example, are special senses because they are located in the head (sensory receptor distribution); exteroceptors because they detect stimuli outside the body (stimulus origin); and photoreceptors because they detect light (modality of stimulus). In comparison, sensory receptors that detect stretch of blood vessels are classified as general senses because they are distributed throughout the body, interoceptors because they detect stimuli within the body, and mechanoreceptors (specifically, baroreceptors) because they detect changes in distension of the organ wall.

Answer 46

Golgi Tendon Organs: proprioceptors located at the junction of a tendon with a muscle. Protect tendons and associated muscles from damage due to excessive tension. Muscle Spindles: proprioceptors found between the skeletal muscle fibers in the muscle belly When a muscle is stretched, the spindle sends a signal to the CNS indicating how much and how fast the muscle's length is changing. Muscle spindles also cause stretch reflex Joint Kinesthetic Receptors: proprioceptors located in and around synovial joints Respond to pressure, acceleration, deceleration, and excessive strain on a joint. Provide feedback about whether movements are two slow, too fast, or in the wrong direction Vestibular Apparatus: a collective group of receptor organs in the inner ear Responds to changes in posture and balance Monitor the position of the head, provide sensory information regarding static equilibrium and the maintenance of body position when motionless. They also contribute to dynamic equilibrium, which is the maintenance of body position in response to movement, by monitoring changes in linear acceleration.

Answer 47

Referred pain occurs when sensory nerve signals from certain viscera are perceived as originating not from the organ, but from somatic sensory receptors within the skin and skeletal muscle. Numerous somatic sensory neurons and visceral sensory neurons conduct nerve signals on the same ascending tracts within the spinal cord. As a result, the somatosensory cortex in the brain is unable to accurately determine the actual source of the stimulus, and thus the stimulus may be localized incorrectly. Misinterpretation of a pain source occurs when nerve signals from two different organs are sent to the brain in a common sensory pathway.

Answer 48

The sensory receptor organ for smell is the olfactory epithelium. This epithelium lines the superior region of the nasal cavity, covering both the inferior surface of the cribriform plate and superior nasal conchae of the ethmoid bone. The olfactory epithelium is composed of three distinct cell types: ∙ Olfactory receptor cells (also called olfactory neurons), which detect odors ∙ Supporting cells (also called sustentacular cells), which sustain the olfactory receptor cells ∙ Basal cells, which function as neural stem cells to continually replace olfactory receptor cells

Answer 49

Odorant --> Receptor cells (axons: CN I) --> Olfactory bulb --> Olfactory tracts --> Temporal lobe (primary olfactory cortex) or Selected different regions including hypothalamus and amygdala Binding of neurotransmitter by secondary neurons results in propagation of nerve signals through the various olfactory pathways. Sensory information reaches different regions of the brain, including the (1) cerebral cortex, which allows us to consciously perceive and identify the smell; (2) hypothalamus, which controls visceral reactions to smell, such as salivation, sneezing, or gagging; and (3) amygdala, which is a center for recognition of odors and often associating those odors to a particular emotion

Answer 50

On the dorsal surface of the tongue are epithelial and connective tis- sue elevations called papillae, which are of four types: filiform, fungiform, foliate, and vallate: Filiform papillae are short and spiked; they are distributed on the anterior two-thirds of the tongue surface. These papillae do not house taste buds and thus, have no role in gustation. Instead, their bristlelike structure serves a mechanical function; they assist in detecting texture and manipulating food. Fungiform papillae are blocklike projections primarily located on the tip and sides of the tongue. Each contains only a few taste buds. Foliate papillae are not well developed on the human tongue. They extend as ridges on the posterior lateral sides of the tongue and house only a few taste buds during infancy and early childhood. Vallate papillae, or circumvallate papillae, are the least numerous (about 10 to 12) yet are the largest papillae on the tongue. They are arranged in an inverted V shape on the posterior dorsal surface of the tongue. Most of our taste buds are housed within the walls of these papillae along the side facing the depression.

Answer 51

Taste buds are cylindrical sensory receptor organs containing cells that have the appearance of an onion. Each taste bud is composed of three distinct cell types: ∙ Gustatory cells (also called gustatory receptors), which detect tastants (taste-producing molecules and ions) in our food ∙ Supporting cells that sustain the gustatory cells ∙ Basal cells, which function as neural stem cells to continually replace the relatively short-lived gustatory cells

Answer 52

Dendritic endings of primary neurons are associated with gustatory cells, with each neuron contacting several gustatory cells. These sensory neurons are primarily components of the facial nerve (CN VII), which innervates taste buds from the anterior two- thirds of the tongue and the glossopharyngeal nerve (CN IX), which innervates taste buds from the posterior one-third of the tongue. Axons within these nerves project to the medulla oblongata (specifically, the nucleus solitarius) to synapse with secondary neurons. These secondary neurons project to the thalamus, and axons of tertiary neurons project to the primary gustatory cortex in the insula of the cerebrum.

Answer 53

Sweet tastes are produced by organic compounds such as sugar or other molecules (e.g., artificial sweeteners). ∙ Salt tastes are produced by metal ions, such as sodium (Na+) and potassium (K+). ∙ Sour tastes are associated with acids in the ingested material, such as hydrogen ions (H+) in vinegar. ∙ Bitter tastes are produced primarily by alkaloids such as quinine, unsweetened chocolate, nicotine, and caffeine. Umami stimuli: Umami (u'ma-mē) is a Japanese word meaning “delicious flavor.” It is a taste related to amino acids, such as glutamate and aspartate, to produce a meaty flavor. association of smell with taste Taste is integrated with temperature, texture, and especially smell Food has less taste if olfaction is blocked (having a cold)

Answer 54

Light rays are straight as they first enter the eye. However, the ability to see clearly requires refraction (or bending) of the light rays so that they hit on the retina—specifically, at the fovea centralis, the portion of the retina that is predominantly composed of cones and pro- vides the sharpest vision. Light rays are refracted when (1) they pass between two media of different densities and (2) these media meet at a curved surface. Each medium—such as air, water, and other clear fluids, and even clear solids such as glass—is assigned a refractive index, a number that represents its comparative density. The refraction of light rays is greater when there is a larger difference in the refractive index between adjacent media, such as between air and water and with increasing curvature of the media surface. Before light can reach the photoreceptor cells, it must pass from the air through the cor- nea, aqueous humor, lens, and vitreous humor, as well as through the cells forming the inner layers of the retina. Both the cornea and lens play a significant role in refraction of light for vision—the cornea because of the relatively large refraction of light that occur as light passes from air into the cornea and the lens because of its ability to change shape. Recall that the curvature of the lens (and thus the refraction of light) can be altered through accommodation by relaxation and contraction of the ciliary muscles

Answer 55

The anterior cavity is subdivided into two chambers by the iris (the colored part of the eye): the anterior chamber, which is located between the iris and cornea, and the posterior chamber, which is located between the iris and the lens. The external layer of the eye wall is called the fibrous tunic, or external tunic. It is composed of the posterior sclera and the anterior cornea. The middle layer of the eye wall is the vascular tunic, also called the uvea. The vascular tunic houses an extensive array of blood vessels, lymph vessels, and the intrinsic muscles of the eye. The most anterior region of the vascular tunic is the iris, which is the colored portion of the eye. The iris is composed of two layers of smooth muscle fibers, melanocytes, and an array of vascular and nervous structures. In the center of the iris is an opening called the pupil, which allows light to enter the eye to reach the retina. The iris controls pupil size, or diameter—and thus the amount of light entering the eye—using its two smooth muscle layers The optic disc contains no photoreceptors. This is where axons of the ganglion cells extend from the back of the eye as the optic nerve. It is commonly called the blind spot because it lacks photoreceptor cells, and no image forms there. The macula lutea is a rounded, yellowish region just lateral to the optic disc. Within the macula lutea is a depressed pit called the fovea centralis, which contains the highest proportion of cones and almost no rods. The lens focuses incoming light onto the retina, and its shape determines the degree of light refraction.

Answer 56

Distant vision: Eyes best adapted for distant vision, far point vision (distance beyond which no change in lens shape needed for focusing) Ciliary muscles relaxed Lens stretched flat by tension in ciliary zone Close vision: light from close objects (<6 m) diverges as approaches eye (requires eye to make active adjustments using three simultaneous processes) accommodation of lenses, constriction of pupils, convergence of eyeballs Accommodation: changing lens shape to increase refraction - Near point vision (closest point on which the eye can focus Constriction: accommodation pupillary reflex constricts pupils to prevent most divergent light rays from entering eye Convergence: medial rotation of eyeballs toward object being views Close vision contracts the ciliary muscle, loosening the ciliary zonule, allowing the lens to bulge

Answer 57

Phototransduction is the converting of light energy into an electrical signal. Photoreceptor cells (rods and cones) are the specific cells within the neural layer of the retina that engage in phototransduction.

Answer 58

Rods * More numerous than cones * Primarily located within peripheral retina * Specialized for dim light, night vision * Cannot distinguish color; poor at sharpness of vision Cones * Less numerous than rods * Primarily located within fovea centralis * Respond to stimulation by bright light * Specialized for color recognition and sharpness of vision * Subdivided into blue, green, and red cones

Answer 59

Each optic nerve conducts visual stimuli information. At the optic chiasm, some axons from the optic nerve decussate. The optic tract on each side then contains axons from both eyes. Visual stimuli information is processed by the thalamus and then interpreted by visual association areas within the occipital lobe of the cerebrum. Visual sensory input involved in reflexes is relayed to nuclei within the midbrain (superior colliculi and pretectal nuclei). Retina Photoreceptors and neurons in the retina process the stimulus from incoming light. Optic nerve Axons of retinal ganglion cells form optic nerves and exit the eye. Optic chiasm Optic nerve axons from the medial region of the retina cross at the optic chiasm; the axons from the lateral region of the retina remain uncrossed. Optic tract The optic tract contains axons from both eyes, and these axons will project to either the thalamus or the midbrain. Lateral geniculate nucleus of thalamus The majority of the optic tract axons project to the lateral geniculate nucleus in the thalamus. Pretectal nucleus of the midbrain Limited number of optic tract axons project to the pretectal nucleus of the midbrain. Superior colliculus of midbrain Some optic tract axons project to the superior colliculus in the midbrain. Primary visual cortex of occipital lobe Receives processed information from the thalamus

Answer 60

-outer ear: auricle, external acoustic meatus, & tympanic membrane -middle ear: auditory ossicles) malleus, incus, & stapes (tensor tympani & stapedius) -inner ear: w/in the bony labyrinth are the portions of the membranous labyrinth for hearing (the cochlear duct) and equilibrium and balance (saccule, utricle, and semicircular ducts). w/in the cochlea, there is the perilymph and the endolymph

Answer 61

-malleus, incus, stapes -the auditory ossicle are responsible for amplifying sound waves from the tympanic membrane to the oval window. when sound waves strike the tympanic membrane, the 3 middle ear ossicles vibrate along with the tympanic membrane, causing the footplate of the stapes to move in and out of the oval window,

Answer 62

The inner ear is located within the petrous part of the temporal bone, where there are spaces, or cavities, called the bony labyrinth. Within the bony labyrinth are membranous, fluid-filled tubes and sacs called the membranous labyrinth. Receptors for both hearing and equilibrium are within the membranous labyrinth. The space between the outer walls of the bony labyrinth and the membranous labyrinth is filled with a fluid called perilymph. The perilymph suspends, supports, and protects the membranous labyrinth from the wall of the bony labyrinth. The space within the membranous labyrinth contains a fluid called endolymph, which is an unusual extracellular fluid because it is similar in composition to intracellular fluid with relatively high levels of K+. The bony labyrinth is structurally and functionally partitioned into three distinct regions, including the cochlea, vestibule, and semicircular canals

Answer 63

The cochlea is a portion of the inner ear that looks like a snail shell. It receives sound in the form of vibrations, which cause the stereocilia to move, which then convert these vibrations into nerve impulses which are taken up to the brain to be interpreted.

Answer 64

1 Sound waves are directed by the auricle into the external acoustic meatus, causing the tympanic membrane to vibrate. 2 Tympanic membrane vibration moves auditory ossicles (malleus, incus, and stapes); sound waves are amplified. 3 The stapes at the oval window generates pressure waves in the perilymph within the scala vestibuli. 4 Pressure waves cause the vestibular membrane to move, resulting in pressure wave formation in the endolymph within the cochlear duct and displacement of a specific region of the basilar membrane. Hair cells in the spiral organ are distorted, initiating nerve signals in the cochlear branch of the vestibulocochlear nerve (CN VIII). 5 Remaining pressure waves are transferred to the perilymph within the scala tympani and are absorbed as the round window bulges slightly.

Answer 65

1 Movement of the basilar membrane produces nerve signals that are propagated along the cochlear branch of CN VIII to the cochlear nucleus within the medulla oblongata. 2a Some secondary neurons relay nerve signals directly to the inferior colliculus of the midbrain. 2b Some secondary neurons relay nerve signals to the superior olivary nucleus within the pons, which are then relayed to the inferior colliculus of the midbrain. 3 Nerve signals are relayed from the inferior colliculus to the thalamus (medial geniculate nucleus). 4 Nerve signals are then relayed from the thalamus to the primary auditory cortex of the temporal lobe of the cerebrum for sound perception.

Answer 66

The term equilibrium refers to our awareness and monitoring of head position. Sensory receptors in the utricle, saccule, and semicircular ducts, collectively called the vestibular apparatus, help monitor and adjust our equilibrium. Our brain receives this sensory input and, along with visual sensory input and input from our proprioceptors, integrates this information so we can keep our balance and make positional adjustments as necessary. The utricle and saccule detect head position during static equilibrium—that is, when the head is stationary. The utricle and saccule also detect linear acceleration changes of the head. This occurs, for example, when you tilt your head downward to look at your shoes. The semicircular ducts, in contrast, are responsible for detecting angular acceleration, or rotational movements of the head.

Answer 67

vestibular apparatus * utricle, saccule, semicircular ducts Maculae detect both the orientation of the head when the body is stationary and the linear acceleration of the head. The maculae are located within the walls of the saccule and utricle. The utricle and saccule make up the part of the vestibular apparatus that senses linear movements. The utricle senses side to side (lateral) movements, whereas the saccule senses movements in the sagittal plane (up/down and forward/back). The utricle and saccule contain hair cells covered by a membrane known as the otolithic membrane. When the head move, certain hair cells bend and depolarize, creating an action potential that signals to the central nervous system. Stereocilia bent toward kinocilium * Hair cells depolarize, increasing neurotransmitter release * Increased nerve signal frequency along vestibular branch of CN VIII Stereocilia bent away from kinocilium * Hair cells hyperpolarize, inhibiting neurotransmitter release * Decreased nerve signal frequency along vestibular branch of CN VIII Rotation of the head causes endolymph within the semicircular duct to push against the cupula covering the hair cells, resulting in bending of their stereocilia and an alteration in the frequency of nerve signal propagation.

Answer 68

Endocrine glands lack ducts. Hormone molecules are instead released from endocrine gland cells into the interstitial fluid and then enter the blood. ∙ These hormone molecules are transported within the blood from the endocrine gland’s associated capillaries by the cardiovascular system to all body tissues, a process that is relatively slow. ∙ There the hormones randomly leave the blood from these capillaries and enter the interstitial fluid, which provides the hormone molecules access to potentially all body cells. Consequently, the response induced by each hormone can be widespread. ∙ The hormone binds to its target cells’ receptors, which may be either in the plasma membrane or within the cell. The binding of hormones to cellular receptors either initiates or inhibits selective metabolic activities within these cells (e.g., activate enzymes, open ion channels, stimulate protein synthesis or cellular division). These altered metabolic activities can have long-lasting effects and may continue after removal of the hormone.

Answer 69

Communication Method Endocrine system - Secretes hormones; hormones are transported within the blood and distributed to target cells throughout body Nervous system - A nerve signal causes neurotransmitter release from a neuron into a synaptic cleft Target of Stimulation Endocrine system - Any cell in the body with a receptor for the hormone Nervous system - Other neurons, muscle cells, and gland cells Response Time Endocrine system - Relatively slow reaction time: Seconds to minutes to hours Nervous system - Rapid reaction time: Typically milliseconds or seconds Range of Effect Endocrine system - Typically has widespread effects throughout the body Nervous system - Typically has localized, specific effects in the body Duration of Response Endocrine system - Long-lasting: Minutes to days to weeks; may continue after stimulus is removed Nervous system - Short-term: Milliseconds; terminates with removal of stimulus

Answer 70

Controlling reproductive activities Controlling digestive processes Maintaining homeostasis of blood composition and volume Regulating development, growth, and metabolism

Answer 71

- Pineal gland within the brain superior and posterior to the Hypothalamus. - Hypothalamus is within the brain anterior and inferior to the Pineal gland. -The Pituitary gland is connected to the Hypothalamus through the infindubulum and is inferior to the Hypothalamus. -The Thyroid gland is in the neck and anterior to the Parathyroid glands. -The Parathyroid glands are posterior to the Thyroid glands. -The Thymus is inferior to the Thyroid/ Parathyroid glands and is anterior to the heart. -The adrenal glands are superior to the kidneys. -The Ovaries/ Testes like medially within the body between each thigh. The testis are exterior to the body whereas the ovaries are internal and inferior to the belly button.

Answer 72

Hormonal stimulation. The stimulus for the release of many hormones from an endocrine gland is the binding of another hormone. An example occurs when thyroid-stimulating hormone (which is released from the anterior pituitary) binds to the thyroid gland to cause release of thyroid hormone. ∙ Humoral stimulation. Some endocrine glands are stimulated to release their hormones in response to a changing level of nutrient molecules or ions within the blood. When either nutrient or ion levels decrease or increase within the blood, an endocrine gland is stimulated to release its hormone molecules. An example of humoral stimulation occurs when blood glucose increases and the pancreas releases insulin. ∙ Nervous system stimulation. A few endocrine glands are stimulated to release hormone(s) by direct stimulation from the nervous system. The classic example is the release of epinephrine and norepinephrine by the adrenal medulla in response to stimulation by the sympathetic division of the autonomic nervous system

Answer 73

Steroids * Lipid-soluble * Formed from cholesterol Examples: Estrogen, progesterone, testosterone, cortisol, aldosterone Biogenic amines Water-soluble (except thyroid hormone) * Derived from amino acid that is modified (e.g., tyrosine) Examples: Norepinephrine, epinephrine, thyroid hormone, melatonin Proteins * Water-soluble * Consists of amino acid chains Examples: Antidiuretic hormone, insulin, glucagon, growth hormone, erythropoietin

Answer 74

Local hormones are a large group of short-lived signaling molecules that do not circulate within the blood like Eicosanoids and Prostaglandins. Instead, cells synthesize and release these molecules, which then bind with either the same cell that produced them (autocrine stimulation) or neighboring cells (paracrine stimulation). These signaling molecules have properties similar to hormones because the released ligands (signaling molecules) initiate and regulate cellular changes. They just do so “in the tissue neighborhood.”

Answer 75

Lipid-soluble hormones (e.g., steroids, calcitriol, thyroid hormone) do not dissolve readily within the aqueous environment of the blood (blood plasma), and so they require carrier molecules. These mole-cules are water-soluble proteins synthesized by the liver. Water-soluble hormones (i.e., most biogenic amines and proteins), in comparison, readily dissolve within the aqueous environment of the blood, and so these hormones do not generally require carrier proteins. Thus, water-soluble hormones are generally released directly into the blood and transported to target cells. Note that some water-soluble hormones (e.g., insulin-like growth factor) are transported by carrier proteins, which function to prolong the life of these hormones.

Answer 76

Hormone release. Hormone release from an endocrine gland and hormone concentration within the blood are positively correlated. An increase in release of the hormone results in a higher hormone concentration within the blood. In contrast, a decrease in release of the hormone results in a lower hormone concentration within the blood. ∙ Hormone elimination. Hormones are typically eliminated (1) through enzymatic degradation, which usually occurs in liver cells, (2) through removal of the hormone from the blood by its excretion from the kidneys as a component of urine, or (3) by uptake into target cells. Hormone elimination and hormone concentration in the blood are negatively correlated. The faster the rate of hormone elimination, the lower the hormone concentration within the blood, whereas the slower the rate of hormone elimination, the higher the hormone concentration within the blood.

Answer 77

Lipid soluble 1 The unbound hormone diffuses readily through the plasma membrane and binds with an intracellular receptor, either within the cytosol or the nucleus to form a hormone-receptor complex. 2 The hormone-receptor complex binds with a specific DNA sequence called a hormone-response element (HRE). 3 Binding of the HRE stimulates mRNA synthesis. 4 mRNA exits the nucleus and is translated by a ribosome in the cytosol. A new protein is synthesized. Water soluble 1 Hormone (first messenger) binds to receptor and induces shape change to activate the receptor. 2 G protein binds to activated receptor 3 GDP is “bumped off” and GTP binds to G protein; G protein is then activated. 4 Activated G protein (with GTP) is released from the receptor and moves along the inside of the plasma membrane, which results in formation or availability of second messenger

Answer 78

Target cells may increase the number of receptors, thereby increasing cell sensitivity to a hormone, a process called up-regulation. In contrast, a target cell may decrease its number of receptors and reduce the target cell’s sensitivity to a hormone through down-regulation A target cell may increase its number of receptors when there is a lower than normal hormone concentration level, or decrease its number of receptors in response to an elevated hormone level. The ability of a target cell to change the number of its available receptors helps to maintain a normal level of cellular response, preventing either understimulation or overstimulation of the target cell. Changes in receptor number also occur as a consequence of developmental maturity, the target cell’s state of activity, and the different stages of the cell cycle.

Answer 79

Synergistic interaction occurs when the activity of one hormone reinforces the activity of another hormone. Synergy means “working together.” Permissive interaction takes place when the activity of one hormone requires a second hormone—as if one hormone “gives permission” for the first hormone to function. Antagonistic interaction occurs when the activity of one hormone opposes the effects of another hormone.

Answer 80

The pituitary gland is also called the hypophysis. It lies inferior to the hypothalamus and is connected to the hypothalamus by a very thin stalk, called either the infundibulum or the infundibular stalk. The hypothalamus is connected to the posterior pituitary by the hypothalamo-hypophyseal tract, and the anterior pituitary by the hypothalamo-hypophyseal portal system.

Answer 81

Hormone is released from the posterior pituitary when a nerve signal is sent from the hypothalamus along the hypothalamo-hypophyseal tract. Specifically, nerve signals from the supraoptic nucleus primarily cause release of ADH, and those from the paraventricular nucleus primarily stimulate release of oxytocin. These molecules are considered hormones, and not neurotransmitters, because they enter the blood when released, even though they are released from synaptic knobs of neurons. Antidiuretic hormone (ADH) functions to help maintain fluid balance, blood volume, and blood pressure. Oxytocin facilitates the movement of sperm through the reproductive ducts in male. Oxytocin (OT) functions in both the delivery of a baby and the ejection of milk in females.

Answer 82

Thyrotropin-releasing hormone (TRH) stimulates the anterior pituitary to release thyroid-stimulating hormone (TSH) (also called thyrotropin). TSH stimulates the thyroid gland to release thyroid hormone (TH), which regulates the metabolic rate. * Prolactin-releasing hormone (PRH) stimulates the anterior pituitary to release prolactin, which acts on mammary glands to influence gland growth and stimulate milk production. Prolactin release is inhibited by prolactin-inhibiting hormone * Gonadotropin-releasing hormone (GnRH) stimulates the anterior pituitary to release both follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which are collectively called gonadotropins. These hormones act on the gonads in both females and males to stimulate development of gametes (oocyte and sperm). The ovaries release estrogen and progesterone; the testes release testosterone * Corticotropin-releasing hormone (CRH) stimulates release of adrenocorticotropic hormone (ACTH) (also called corticotropin). ACTH stimulates the adrenal cortex to produce and secrete glucocorticoids (e.g., cortisol), which raise blood levels of nutrient molecules (e.g., glucose). * Growth hormone–releasing hormone (GHRH) stimulates the anterior pituitary to release growth hormone (GH) (or somatotropin). GH stimulates the liver to release both insulin-like growth factor 1 and 2 (IGF-1 and IGF-2) . GH and IGFs function synergistically to cause growth.

Answer 83

1. STIMULUS Variables that influence the release of GHRH from the hypothalamus: * Negative feedback by growth hormone * Age * Time of day * Nutrient levels in the blood * Stress and exercise 2. RECEPTOR The hypothalamus responds to various stimuli. 3. CONTROL CENTER The hypothalamus releases growth hormone–releasing hormone (GHRH) into the hypothalamo-hypophyseal portal system. 4. In response to GHRH, the anterior pituitary releases growth hormone (GH). 5. GH stimulates hepatocytes to release insulin-like growth factor (IGFs) into the blood. 6. Both GH and IGFs stimulate target cells (effectors). NET EFFECT 7. Increased protein synthesis, cellular division, and cell differentiation occur— especially in cartilage, bone, and muscle; release of stored nutrients into the blood. 8. Increased levels of both GH and IGFs inhibit the release of GHRH from the hypothalamus; Increased levels of GH also inhibits the release of GH from the anterior pituitary.

Answer 84

Bone Muscle All cells Increased growth Increased amino acid uptake, which results in protein synthesis Stimulated cellular division Cell differentiation Liver tissue Increased glycogenolysis and gluconeogenesis Decreased glycogenesis Adipose connective tissue Increased lipolysis Decreased lipogenesis

Answer 85

The thyroid gland is a butterfly-shaped gland located immediately inferior to the thyroid cartilage of the larynx and anterior to the trachea. This gland is composed of left and right lobes, which are connected at the anterior midline by a narrow isthmus

Answer 86

The follicular cells produce and later release thyroid hormone (TH) by first synthesizing a glycoprotein called thyroglobulin (TGB) and secreting it by exocytosis into the colloid-filled lumen Parafollicular cells—which are the other, less numerous endocrine cells of the thyroid—are located around the follicular cells. These cells synthesize and release calcitonin

Answer 87

All cells, especially neurons Increased metabolic rate Increased glucose uptake Liver tissue Increased glycogenolysis and gluconeogenesis Decreased glycogenesis Adipose connective tissue Increased lipolysis Decreased lipogenesis Lungs Increased breathing rate Heart Increased heart rate Increased force of contraction These responses help meet increased O2 demand for aerobic cellular respiration.

Answer 88

Calcitonin is synthesized and released from the less numerous cells of the thyroid gland call the parafollicular cells. These cells are located around the follicular cells that produce thyroid hormone. The stimulus for calcitonin release from parafollicular cells is a high blood calcium level; it is also secreted in response to stress from exercise. Calcitonin primarily inhibits osteoclast activity within bone tissue (which decreases the breakdown of bone tissue) and stimulates the kidneys to increase the loss of calcium in the urine. The net effect of calcitonin is a reduction in blood calcium levels.

Answer 89

The adrenal glands, or suprarenal glands, are paired, pyramid-shaped endocrine glands anchored on the superior surface of each kidney. These glands (like the kidney that each is superior to) are retroperitoneal, which is posterior to the parietal peritoneum. Each adrenal gland is embedded within fat and fascia to minimize their movement. Two regions constitute an adrenal gland: the adrenal medulla and the adrenal cortex

Answer 90

Zona glomerulosa - Mineralocorticoids: hormones that regulate electrolyte levels Zona fasciculata - Glucocorticoids: hormones that regulate blood sugar Zona reticularis - Gonadocorticoids: sex hormones

Answer 91

The hypothalamus responds to particular stimuli by releasing corticotropin- releasing hormone (CRH), which stimulates the anterior pituitary to release adrenocorticotropic hormone (ACTH). ACTH stimulates the adrenal cortex to release cortisol. Cortisol increases the availability of nutrient molecules to support the response to stress. Liver Increased glycogenolysis and gluconeogenesis Decreased glycogenesis Adipose connective tissue Increased lipolysis Decreased lipogenesis High doses of cortisol Increase retention of Na+, H2O Decrease inflammation Suppress the immune system Inhibit connective tissue repair All cells Stimulation of protein catabolism (occurs in all cells except hepatocytes) Decreased glucose uptake

Answer 92

The pancreas is an elongated organ situated posterior to the stomach. The vast majority of the cells of the pancreas serve an exocrine gland function. These cells, specifically called acinar cells, are modified simple cuboidal epithelial cells arranged in saclike acini. Each is specifically called a pancreatic acinus. The pancreatic acini serve as an exocrine gland by producing digestive enzymes, which are released into the pancreatic ducts and ultimately into the duodenum region of the small intestine

Answer 93

The endocrine cells of the pancreas are located within small clusters called pancreatic islets, also known as islets of Langerhans. These endocrine cell clusters form only about 1% of the total pancreatic volume. A pancreatic islet is composed of two primary types of cells: alpha cells, which secrete glucagon, and beta cells, which secrete insulin. Minor cells within the pancreatic islets include delta cells, which secrete somatostatin (also described as growth hormone–inhibiting hormone), and F cells, which secrete pancreatic polypeptide.

Answer 94

The release of insulin results in both a decrease in all nutrients in the blood and an increase in the synthesis of the storage form of these molecules within body tissues. By decreasing alternative nutrients (fatty acids and amino acids), the cells of the body are more likely to use the available glucose within the blood and help return blood glucose to a normal level more quickly. The release of insulin is controlled by negative feedback; as blood glucose levels decrease, less insulin is released from the pancreas. Liver tissue Increased glycogenesis Decreased glycogenolysis and gluconeogenesis Adipose connective tissue Increased lipogenesis Decreased lipolysis All cells (especially muscle) Increased uptake of amino acids, which stimulates protein anabolism Most cells Increased uptake of glucose by increasing glucose transport proteins in the plasma membrane

Answer 95

Glucagon is released from alpha cells within pancreatic islets in response to low blood glucose levels. Glucagon binds with target cells that increase glucose, glycerol, and fatty acid levels within the blood. Liver Increased glycogenolysis and gluconeogenesis Decreased glycogenesis Adipose connective tissue Decreased lipogenesis Increased lipolysis

Answer 96

The pineal gland (or pineal body) is a small, cone-shaped structure forming the posterior region of the epithalamus within the diencephalon. The pineal gland secretes melatonin, which makes us drowsy.

Answer 97

There are two different types of cells in the parathyroid glands: chief cells and oxyphil cells. The more common chief cells, or principal cells, are the source of parathyroid hormone (PTH), which is released from the parathyroid gland in response to a decrease in blood calcium levels. Parathyroid hormone functions to increase blood calcium levels. It stimulates release of calcium from bone tissue, decreases loss of calcium in urine, and causes the kidney to release an enzyme to convert the inactive cal- cidiol hormone to the active calcitriol hormone

Answer 98

The T-lymphocytes migrate to the thymus following their formation in the bone marrow, and epithelial cells there secrete thymic hormones (i.e., thymosin, thymulin, and thymopoietin), which participate in the maturation of T-lymphocytes Endocrine tissue within the atria of the heart synthesizes and releases the hormone atrial natriuretic peptide (ANP) in response to increased stretch of the atrial wall. This peptide hormone stimulates both the kidneys to increase urine output (which decreases blood volume) and the blood vessels to dilate. Endocrine tissue within the kidneys release erythropoietin (EPO) when specialized receptors (chemoreceptors) with- in the kidney detect low blood oxygen levels. EPO stimulates red bone marrow to increase the production rate of red blood cells (erythrocytes), which are the oxygen-carrying cells. The liver releases insulin-like growth factors (IGFs) in response to growth hormone. The liver also releases angiotensinogen, an inactive hormone. The activation of angiotensinogen to angiotensin II (the active form of the hormone) requires both an enzyme released from the kidney (renin) and an enzyme anchored within the inner lining of blood vessels The stomach both synthesizes and releases gastrin. A primary function of gastrin is to increase stomach activity to facilitate digestion within the stomach. The small intestine releases both secretin and cholecystokinin, both of which function to facilitate digestion within the small intestine. Ultraviolet light penetrates into surface skin cells (keratinocytes) to convert modified cholesterol molecules to vitamin D3 (cholecalciferol), which is then released into the blood. Vitamin D3 is converted to calcidiol by an enzyme within the liver and then by an enzyme within the kidney to calcitriol, the active hormone. Adipose connective tissue is located throughout the body, and it releases the hormone leptin. This hormone helps to regulate food intake by binding to the neurons within the hypothalamus that control appetite. Lower percentage of body fat is associated with lower blood levels of leptin, which stimulates the appetite.