chapter 3 reading - in exam Flashcards

Question

central sulcus

Answer 1

The sulcus that separates the frontal lobe from the parietal lobe.

Answer 2

the base of the somatosensory cortex and a portion of the insular cortex, which is normally hidden from view by the frontal and temporal lobes, receive information about taste.

Answer 3

With the exception of olfaction (smell) and gustation (taste), sensory information from the body or the environment is sent to the primary sensory cortex of the contralateral hemi- sphere. For example, the primary somatosensory cortex of the left hemisphere learns what the right hand is holding; the left primary visual cortex learns what is happening toward the person’s right.

Answer 4

The regions of primary sensory and motor cortex occupy only a small part of the cerebral cortex. The rest of the cerebral cortex accomplishes what is done be- tween sensation andaction:perceiving,learning and remembering, planning, and acting. These processes take place in the association areas of the cerebral cortex. The central sulcus provides an important dividing line between the rostral and caudal regions of the cerebral cortex. (Look once more at Figure 3.9.) The rostral region is involved in movement-related activities, such as planning and executing behaviors. The caudal region is involved in perceiving and learning.

Answer 5

Each primary sensory area of the cerebral cortex sends information to adjacent regions, called the sensory association cortex. Circuits of neurons in the sensory association cortex analyze the information received from the primary sensory cortex; perception takes place there, and memories are stored there. The regions of the sensory association cortex located closest to the primary sensory areas receive information from only one sensory system. For example, the region closest to the primary visual cortex analyzes visual information and stores visual memories. Regions of the sensory association cortex located far from the pri- mary sensory areas receive information from more than one sensory system and are involved in several kinds of perceptions and memories. These regions make it possible to integrate information from more than one sensory system. For example, we can learn the connection between the sightof a particular faceand the sound of a particular voice. This type of learning requires information from visual and auditory association areas (see Chapter 7). If people sustain damage to the somatosensory association cortex, their deficits are related to somatosensation and to the environment in general. For example, they may have difficulty perceiving the shapes of objects that they can touch but not see, they may be unable to name parts of their bodies (see the following case of Mr. M.), or they may have trouble drawing maps or following them. Although people who sustain damage to the visual association cortex will not become blind, they may be unable to recognize objects by sight. People who sustain damage to the auditory association cortex may have difficulty perceiving speech or even producing meaningful speech of their own. People who sustain damage to regions of the association cortex at the junction of the three posterior lobes, where the somatosensory, visual, and auditory functions overlap, may have difficulty reading or writing.

Answer 6

The region of the cerebral cortex that is most directly involved in the control of movement is the primary motor cortex, located just in front of the primary somatosen- sory cortex. Neurons in different parts of the primary motor cortex are connected to muscles in different parts of the body. The connections, like those of the sensory regions of the ce- rebral cortex, are contralateral. This means that the left primary motor cortex controls the right side of the body and vice versa. For example, if a surgeon places an electrode on the surface of the primary motor cortex and stimulates the neurons there with a weak electrical current, the result will be contralateral movement of a particular part of the body. Moving the electrode to a different spot will cause a different part of the body to move. (Look again at Figure 3.9.) You can think of the strip of primary motor cortex as the keyboard of a piano, with each key controlling a different movement. (We will see shortly who is the “player” of this piano.)

Answer 7

Just as regions of the sensory association cortex of the posterior part of the brain are involved in perceiving and remembering, the frontal association cortex is involved in the planning and execution of movements. The motor association cortex (also known as the premotor cortex) is located just rostral to the primary motor cortex. Because this region controls the primary motor cortex, it directly controls behavior. If the primary motor cortex is the keyboard of the piano, then the motor association cortex is the piano player. The rest of the frontal lobe, rostral to the motor association cortex, is known as the prefrontal cortex. This region of the brain is less involved with the control of movement and more involved in formulating plans and strategies.

Answer 8

Although the two cerebral hemispheres cooperate with each other, they do not perform identical functions. Some functions are lateralized— located primarily on one side of the brain. In general, the left hemisphere participates in the analysis of information—the extraction of the elements that make up the whole of an experi- ence. This ability makes the left hemisphere particularly good at recognizing serial events— events whose elements occur one after the other—and controlling sequences of behavior. (In a few people, the functions of the left and right hemispheres are reversed.) The serial functions that are performed by the left hemisphere include verbal activities, such as talking, understanding the speech of other people, reading, andwriting. These abilities are disrupted by damage to the various regions of the left hemisphere. (We will say more about language and the brain in Chapter 14.) In contrast, the right hemisphere is specialized for synthesis; it is particularly good at putting isolated elements together to perceive things as a whole. For example, our ability to draw sketches (especially of three-dimensional objects), read maps, and construct complex objects out of smaller elements depends heavily on circuits of neurons that are located in the right hemisphere. Damage to the right hemisphere disrupts these abilities.

Answer 9

As we go about our daily lives, we are not aware of the fact that each hemisphere per- ceives the world differently. Although the two cerebral hemispheres perform somewhat differ- ent functions, our perceptions and our memories are unified. This unity is accomplished by the corpus callosum, a largeband of axons that connectscorresponding parts of thecerebral cortex of the left and right hemispheres: The left and right temporal lobes are connected, the left and right parietal lobes are connected,and so on. Because of thecorpus callosum,each region of the association cortex knows what is happening in the corresponding region of the opposite side of the brain. The corpus callosum also makes a few asymmetrical connections that link different regions of the two hemispheres.

Answer 10

The brain (and part of the spinal cord) has been sliced down the middle, dividing it into its two symmetrical halves. The left half has been re- moved, so we see the inner surface of the right half. The cerebral cortex covers most of the surface of the cerebral hemispheres (including the frontal, parietal, occipital, and temporal lobes). Another form of ce- rebral cortex, the limbic cortex, is located around the medial edge of the cerebral hemispheres (limbus means “border”). The cingulate gyrus, an important region of the limbic cortex, can be seen in Figure 3.11. The limbic cortex, along with other parts of the brain, form the limbic system. Besides the limbic cortex, the most important parts of the limbic system are the hippocampus (“sea horse”) and the amygdala (“almond”), located next to the lateral ventricle in the temporal lobe. The for- nix (“arch”) is a bundle of axons that connects the hippocampus with other regions of the brain, includ- ing the mammillary (“breast-shaped”) bodies, pro- trusions on the base of the brain that contain parts of the hypothalamus. (See Figure 3.12.) We now know that parts of the limbic system (notably, the hippocampal formation and the region of limbic cortex that surrounds it) are involved in learning and memory. The amygdala and some regions of the limbic cortex are specifically involved in emotions: feelings and expressions of emotions, emotional memories, and recog- nition of the signs of emotions in other people.

Answer 11

The basal ganglia are a collection of nuclei below the cortex in the fore- brain, which lie beneath the anterior portion of the lateral ventricles. Nuclei are groups of neurons of similar shape. (The word nucleus can refer to the inner portion of an atom, to the structure of a cell that contains the chromosomes, and—as in this case—to a col- lection of neurons located within the brain.) The major parts of the basal ganglia are the caudate nucleus, the putamen, and the globus pallidus (the “nucleus with a tail,” the “shell,” and the “pale globe”). (See Figure 3.13.) The basal ganglia are involved in the control of movement. For example, Parkinson’s disease is caused by the degeneration of certain neurons located in the midbrain that send axons to the caudate nucleus and the puta- men. The symptoms of this disease are weakness, tremors, rigidity of the limbs, poor balance, and difficulty in initiating movements.

Answer 12

The thalamus (from the Greek thalamos, “inner chamber”) makes up the dor- sal part of the diencephalon. It is located near the middle of the cerebral hemispheres, immediately medial and caudal to the basal ganglia. (Look again at Figure 3.13.). The thala- mus has two lobes, connected by a bridge of gray matter called the massa intermedia. Most neural input to the cerebral cortex is received from the thalamus; indeed, much of the cortical surface can be divided into regions that receive projections from specific parts of the thalamus. The thalamus is divided into several nuclei. Some thalamic nuclei receive sensory information from the sensory systems. The neurons in these nuclei then relay the sensory information to specific sensory projection areas of the cerebral cortex. For example, the lateral geniculate nucleus receives information from the eye and sends axons to the pri- mary visual cortex, and the medial geniculate nucleus receives information from the inner ear and sends axons to the primary auditory cortex. Other thalamic nuclei project to specific regions of the cerebral cortex, but they do not relay sensory information.

Answer 13

The second major division of the forebrain, the diencephalon, is situated between the telencephalon and the mesencephalon; it surrounds the third ven- tricle. Its two most important structures are the thalamus and the hypothalamus.

Answer 14

receives information from the cerebellum and projects it to the primary motor cortex. Still other nuclei receive infor- mation from one region of the cerebral cortex and relay it to another region. Several nuclei are involved in controlling the general excitabil- ity of the cerebral cortex. To accomplish this task, these nuclei have widespread projections to all cortical regions.

Answer 15

The hypothalamus is located under the thalamus. Although the hypothalamus is a relatively small structure, it is an im- portant one. It controls the autonomic nervous system and the endo- crine system and organizes behaviors related to the survival of the species, such as fighting, escape, eating, and reproduction. The hypothalamus is situated on both sides of the ventral por- tion of the third ventricle. The hypothalamus is a complex structure, containing many nuclei and fiber tracts. Figure 3.14 indicates its loca- tion and size. Note that the pituitary gland is attached to the base of the hypothalamus via the pituitary stalk. Just in front of the pituitary stalk is the optic chiasm, where half of the axons in the optic nerves (from the eyes) cross from one side of the brain to the other. The hypo- thalamus controls many behaviors, such as drinking and sleeping. Much of the endocrine system is controlled by hormones produced by cells in the hypothalamus. A special system of blood vessels directly connects the hypothalamus with the anterior pitu- itary gland. (See Figure 3.15) The hypothalamic hormones are secreted by specialized neurons called neurosecretory cells, located near the base of the pituitary stalk. These hormones stimulate the anterior pituitary gland to secrete its hormones. For example, gonadotropin-releasing hormone causes the anterior pituitary gland to secrete the gonadotropic hormones, which play a role in reproductive physiology and behavior. Most of the hormones secreted by the anterior pituitary gland control other endocrine glands. For example, the gonadotropic hormones stimulate the gonads (ovaries and tes- tes) to release male or female sex hormones. These hormones affect cells throughout the body, including some in the brain. Two other anterior pituitary hormones—prolactin and somatotropic hormone (growth hormone)—do not control other glands but act as the final messenger.

Answer 16

The hypothalamus also produces and controls the secretion of the hormones of the posterior pituitary gland. These hormones include oxytocin and vasopressin. Oxytocin and vasopressin are involved in a number of different physiological and behavioral functions, including pair bonding and parental behavior, which you can read more about in Chapter 9. They are produced by neurons in the hypothalamus whose axons travel down the pituitary stalk and terminate in the posterior pituitary gland. The hormones are carried in vesicles through the axoplasm of these neurons and collect in the terminal buttons in the posterior pituitary gland. When these axons fire, the hormone contained within their terminal but- tons is released and enters the circulatory system.

Answer 17

surrounds the cerebral aqueduct and consists of two major parts: the tectum and the tegmentum.

Answer 18

The tectum (“roof”) is located in the dorsal portion of the mesencephalon. Its principal structures are the superior colliculi and the inferior colliculi, which appear as four bumps on the dorsal surface of the brain stem. The brain stem includes the midbrain and the hindbrain, and it is called the brain stem because it looks just like that: a stem. Figure 3.17 shows several views of the brain stem: lateral and posterior views of the brain stem inside a semitransparent brain, an enlarged view of the brain stem with part of the cerebellum cut away to reveal the inside of the fourth ventricle, and a cross section through the midbrain. The inferior colliculi are a part of the auditory system. The superior colliculi are part of the visual system. In mammals, they are primarily involved in visual reflexes and reactions to moving stimuli.

Answer 19

The tegmentum (“covering”) consists of the portion of the mesencephalon beneath the tectum. It includes the rostral end of the reticular formation, several nuclei controlling eye movements, the periaqueductal gray matter, the red nucleus, the substantia nigra, and the ventral tegmental area.

Answer 20

Alarge network of neural tissue located in the central region of the brain stem, from the medulla to the diencephalon.

Answer 21

The region of the midbrain surrounding the cerebral aqueduct; contains neural circuits involved in species-typical behaviors.

Answer 22

Alarge nucleus of the midbrain thatreceives input from the cerebellum and motor cortexand sends axons to motor neurons in thespinal cord.

Answer 23

A darkly stained re- gion of the tegmentum that contains neu- rons that communicatewith the caudate nucleus and putamen in the basal ganglia.

Answer 24

which surrounds the fourth ventricle, consists of two major divisions: the metencephalon and the myelencephalon.

Answer 25

The metencephalon consists of the cerebellum and the pons. The cerebel- lum is critical in coordinating movementswhile the pons is important in sleep/wake regulation.

Answer 26

The cerebellum (“little brain”), with its two hemispheres, resembles a miniature version of the cerebrum. It is covered by the cerebellar cortex and has a set of deep cerebellar nuclei. These nuclei receive projections from the cerebellar cor- tex and themselves send projections out of the cerebellum to other parts of the brain. Each hemisphere of the cerebellum is attached to the dorsal surface of the pons by bun- dles of axons: the superior, middle, and inferior cerebellar peduncles (“little feet”). (See Figure 3.17c.) Musicians, artists and athletes owe much to their cerebellums. The cerebel- lum receives visual, auditory, vestibular, and somatosensory information, and it also receives information about individual muscle movements being directed by the brain. The cerebellum integrates this information and modifies the motor outflow, exerting a coordinating and smoothing effect on the movements. Cerebellar damage results in jerky, poorly coordinated, exaggerated movements; extensive cerebellar damage makes it impossible even to stand.

Answer 27

The pons, a large bulge in the brain stem, lies between the mesencephalon and me- dulla oblongata, immediately ventral to the cerebellum. Pons means “bridge,” but it does not really look like one. The pons contains, in its core, a portion of the reticular formation, including some nuclei that appear to be important in sleep and arousal. It also contains a large nucleus that relays information from the cerebral cortex to the cerebellum.

Answer 28

The myelencephalon contains one major structure, the medulla oblongata (literally, “oblong marrow”), usually just called the medulla. This structure is the most caudal portion of the brain stem; its lower border is the rostral end of the spinal cord. (Refer again to Figure 3.17c.) The medulla contains part of the reticular formation, including nuclei that control vital functions such as regulation of the cardiovascular system, respira- tion, and skeletal muscle tone.

Answer 29

The spinal cord is a long, tubelike structure, wider at the top than the bottom. The principal functions of the spinal cord are to distribute motor fibers to the effector organs of the body (glands and muscles) and to col- lect somatosensory information to be passed on to the brain. The spinal cord can sometimes function independently of the brain. For example, some reflex circuits involve only the spinal cord and not the brain (see Figure 3.18). The spinal cord is protected by the vertebral column, which is com- posed of twenty-four individual vertebrae of the cervical (neck), thoracic (chest), and lumbar (lower back) regions and the fused vertebrae that make up the sacral and coccygeal portions of the column (located in the pelvic region). The spinal cord passes through a hole in each of the vertebrae (the spinal foramen). Figure 3.18 illustrates the divisions and structures of the spinal cord and vertebral column. The spinal cord is only about two- thirds as long as the vertebral column; the rest of the space is filled by spinal roots composing the cauda equina (“horse’s tail”). (See Figure 3.1.) To produce the caudal block that is sometimes used in pelvic surgery or childbirth, a local anesthetic can be injected into the CSF contained within the sac of dura mater surrounding the cauda equina. The drug blocks con- duction in the axons of the cauda equina. Figure 3.19a shows a portion of the spinal cord, with the layers of the meninges that wrap it. Small bundles of fibers emerge from each side of the spinal cord in two straight lines along its dorsolateral and ventrolateral surfaces. Groups of these bundles fuse together and become the thirty-one paired sets of dorsal roots and ventral roots. The dorsal and ventral roots join together as they pass through the intervertebral foramens and become spinal nerves. Figure 3.19b shows a cross section of the spinal cord. Like the brain, the spinal cord consists of white matter and gray matter. Unlike the brain’s white matter, the spinal cord’s white matter (consisting of ascending and descending bundles of myelinated axons) is on the outside and the gray matter (mostly neural cell bodies and short, unmyelinated axons) is on the inside. In Figure 3.19b, ascend- ing tracts are indicated in blue; descending tracts are indicated in red.

Answer 30

The brain and spinal cord communicate with the rest of the body via the cranial nerves and spinal nerves. These nerves are part of the PNS, which conveys sensory information to the CNS and conveys messages from the CNS to the body’s muscles and glands.

Answer 31

Twelve pairs of cranial nerves are attached to the ventral surface of the brain. Most of these nerves serve sensory and motor functions of the head and neck region. One of them, the tenth, or vagus nerve, regulates the functions of organs in the thoracic and abdominal cavities. It is called the vagus (“wandering”) nerve because its branches wander throughout the thoracic and abdominal cavities. (The word vagabond has the same root.) Figure 3.20 presents a view of the base of the brain and illustrates the cranial nerves and the structures they serve. Note that efferent (motor) fibers are drawn in red and that afferent (sensory) fibers are drawn in blue. As we mentioned in the previous section, cell bodies of sensory nerve fibers that enter the brain and spinal cord (except for the visual system) are located outside the central ner- vous system. Somatosensory information (and the sense of taste) is received via the cranial nerves. Olfactory information is received via the olfactory bulbs, which receive information from the olfactory receptors in the nose. The olfactory bulbs are complex structures that con- tain a considerable amount of neural circuitry; actually, they are part of the brain.

Answer 32

The spinal nerves begin at the junction of the dorsal and ventral roots of the spinal cord. The nerves leave the vertebral column and travel to the muscles or sensory receptors they innervate (or supply), branching repeatedly as they go. Branches of spinal nerves often fol- low blood vessels, especially those branches that innervate skeletal muscles. Let’s consider the pathways by which sensory information enters the spinal cord and motor information leavesit.The cell bodies of all axons that bring sensory information into the brain and spinal cord are located outside the CNS. (The sole exception is the visual system; the retina of the eye is actually a part of the brain.) These incoming axons are referred to as afferent axons, meaning that the direction of information is inward, toward the CNS. The cell bodies that give rise to the axons that bringsomatosensory information to the spinal cord reside in the dorsal root ganglia, rounded swellings of the dorsal root. (See Figure 3.21.) The axonal stalk divides close to the cellbody,sending one limbinto the spinal cord andthe otherlimb outto the sensory organ. Note that all of the axons in the dorsal root convey somatosensory information. Cell bodies that give rise to the ventral root are located within the gray matter of the spinal cord. The axons of these multipolar neurons leave the spinal cord via a ventral root, which joinsa dorsal root tomake a spinalnerve.The axons that leave the spinal cord through the ventral roots control muscles and glands. They are referred to as efferent axons, meaning that the direction of information is outward, away from the CNS.

Answer 33

The part of the PNS that we have discussed so far—that receives sensory information from the sensory organs and that controls movements of the skeletal muscles—is called the somatic nervous system. The other branch of the PNS—the autonomic nervous system (ANS)—is concerned with regulation of smooth muscle, cardiac muscle, and glands. Smooth muscle is found in the skin, in blood vessels, in the eyes, and in the walls and sphincters of the gut, gallbladder, and urinary bladder, and its regulation is critical for keeping us alive. The ANS consists of two anatomically separate systems: the sympathetic division and the parasympathetic division. With few exceptions, organs of the body are innervated by both of these subdivisions, and each has a different effect. For example, the sympathetic division speeds the heart rate, whereas the parasympathetic division slows it.

Answer 34

The sympathetic division is most involved in activities associated with the expenditure of energy from reserves that are stored in the body. For example, when an organism is excited, the sympathetic nervous system increases blood flow to skeletal muscles, stimulates the secretion of epinephrine (resulting in increased heart rate and a rise in blood sugar level), and causes piloerection (erection of fur in mammals that have it and production of “goose bumps” in humans). Sometimes the sympathetic division is described as coordinating fight, flight, or freeze responses to a stressor. The cell bodies of sympathetic motor neurons are located in the gray matter of the thoracic and lumbar regions of the spinal cord (the sympathetic nervous system is also known as the thoracolumbar system). The fibers of these neurons exit via the ventral roots. After joining the spinal nerves, the fibers branch off and pass into sympathetic ganglia (not to be confused with the dorsal root ganglia). Figure 3.22 shows the relationship of these ganglia to the spinal cord. Note that individual sympathetic ganglia are connected to the neighboring ganglia above and below to form the sympathetic ganglion chain. The axons that leave the spinalcord through the ventralroot belong to the preganglionic neurons. Sympathetic preganglionic axons enter the ganglia of the sympathetic chain. Most of the axons form synapses there, but others pass through these ganglia and travel to one of the sympathetic ganglia located among the internal organs. With one exception, all sym- pathetic preganglionic axons form synapses with neurons located in one of the ganglia. The neurons with which they form synapses are called postganglionic neurons. The postgan- glionic neurons send axons to the target organs, such as the intestines, stomach, kidneys, or sweat glands.

Answer 35

The parasympathetic division of the ANS supports activities that are involved with increases in the body’s supply of stored energy. These activities include salivation, gastric and intestinal motility, secretion of digestive juices, and increased blood flow to thegastrointestinal system. Sometimes theparasympathetic divi- sion is described as coordinating the rest and relax responses after the body has been stressed. Cell bodies that give rise to preganglionic axons in the parasympathetic nervous system are located in two regions: the nuclei of some of the cranial nerves (especially the vagus nerve) and the intermediate horn of the gray matter in the sacral region of the spinal cord. Because of this, the parasympathetic division of the ANS can also be referred to as the cra- niosacral system. Parasympathetic ganglia are located in the immediate vicinity of the target organs; the postganglionic fibers are therefore relatively short. The terminal buttons of both preganglionic and postganglionic neurons in the parasympathetic nervous system secrete acetylcholine.

Answer 36

somatic nervous system spinal nerves afferents from sense organs efferents to muscles cranial nerves afferents from sense organs efferents to muscles autonomic nervous system sympathetic branch spinal nerves (from thoracic and lumbar regions) sympathetic ganglia parasympathetic branch cranial nerves (3rd, 7th, 9th and 10th) spinal nerves (from sacral region) parasympathetic ganglia (adjacent to target organs)

chapter 3 reading - in exam Flashcards

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