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Saladin 5e Extended Outline Chapter 14 The Brain and Cranial Nerves I. Overview of the Brain (pp. 515–520) A. The brain of vertebrates has changed a great deal over evolutionary time; in average humans, the size of the brain is proportional to body size, not to intelligence. (p. 515) B. The brain has been assigned major landmarks as reference points for its study. (pp. 515–518) 1. Two directional terms are rostral (“toward the nose,” or the forehead in upright humans) and caudal (“toward the tail,” or the spinal cord in humans). 2. The brain can be divided conceptually into the cerebrum, cerebellum, and brainstem. a. The cerebrum is about 83% of the brain volume and consists of two cerebral hemispheres. (Fig. 14.1a) i. Each hemisphere has thick folds called gyri separated by shallow grooves called sulci. ii. The deep longitudinal fissure separates the right and left hemispheres. iii. At the bottom of this fissure the hemispheres are connected by the corpus callosum. (Fig. 14.2) b. The cerebellum, the second largest region of the brain containing over 50% of the brain’s neurons, occupies the posterior cranial fossa inferior to the cerebrum. (Fig. 14.1b, c) c. The brainstem is that which remains of the brain if the cerebrum and cerebellum are removed. i. Its major components, rostral to caudal, are the diencephalon, midbrain, pons, and medulla oblongata. (Figs. 14.1b, 14.2) ii. It is oriented like a vertical stalk with the cerebrum perched on top in a living person; postmortem changes give it an oblique angle. iii. The brainstem ends at the foramen magnum, and the CNS continues below this as the spinal cord. C. The brain, like the spinal cord, is composed of gray matter and white matter. (p. 518) (Figs. 14.5, 14.6c) 1. White matter has a bright pearly white color due to myelin around its nerve fibers. 2. Gray matter has little myelin and a duller white color. a. Gray matter forms a surface layer called the cortex over the cerebrum and cerebellum. Saladin Outline Ch.14 Page 2 b. Deeper masses called nuclei are surrounded by white matter. c. In most of the brain, the white matter lies deep to the cortical gray matter, opposite from their relation in the spinal cord. d. White matter in the brain is composed of tracts, or bundles of axons. D. Embryonic development of the brain produces the mature brain anatomy consisting of forebrain, midbrain, and hindbrain.(pp. 518–520) (Fig. 14.3) 1. The nervous system develops from ectoderm; early in the third week of development, a dorsal streak called the neuroectoderm appears along the embryo’s length and thickens to form the neural plate. a. The neural plate gives rise to most neurons and all glial cells except microglia, which arise from mesoderm. b. The neural plate sinks and its edges thicken, forming a neural groove with a raised neural fold. c. The neural folds then fuse along the midline, beginning in the cervical (neck) region and progressing in both directions. 2. By four weeks of development, the neural tube has formed and closed, and it separates from the overlying ectoderm. a. The neural tube grows lateral processes that later form motor nerve fibers. b. The lumen becomes a fluid filled space that later constitutes the central canal of the spinal cord and ventricles of the brain. 3. As the neural tube develops, some ectodermal cells originally along the margin of the groove separate and form two neural crests on each side of the tube. a. Neural crest cells give rise to the arachnoid mater and pia mater; most of the PNS including sensory and autonomic nerves, ganglia, and Schwann cells; and some other structures of the skeletal, integumentary, and endocrine systems. 4. By the fourth week, the neural tube exhibits three primary vesicles: the forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon). (Fig. 14.4) 5. By the fifth week, the neural tube continues to subdivide into five secondary vesicles. (Fig. 14.4) a. The forebrain becomes the telencephalon and diencephalon. (Fig. 14.4b) i. The telenecephalon has a pair of lateral outgrowths that become the cerebral hemispheres. ii. The diencephalon has a pair of small cuplike optic vesicles that become the retinas. b. The midbrain is undivided and retains the name mesencephalon. c. The hindbrain becomes the metencephalon and the myelencephalon. Saladin Outline Ch.14 Page 3 II. Meninges, Ventricles, Cerebrospinal Fluid, and Blood Supply (pp. 520–524) A. The brain is enveloped in three connective tissue membranes, the meninges, which lie between the nervous tissue and bone. (pp. 520–521) 1. The three membranes of the meninges are the dura mater, arachnoid mater, and pia mater. (Fig. 14.5) 2. In the cranial cavity, the dura mater consists of two layers, the outer periosteal layer and the inner meningeal layer. a. Only the meningeal layer continues into the vertebral canal, where it forms the dural sac. b. The dura mater is pressed closely against the cranial bone, but is not attached except in limited places (foramen magnum, sella turcica, crista galli, and sutures). c. In some places the two layers of the dura are separated by dural sinuses. i. The superior sagittal sinus is found just under the cranium along the median line. ii. The transverse sinus runs horizontally from the rear of the head toward each ear. iii. These sinuses meet like an inverted T at the back of the brain and ultimately empty into the internal jugular veins. d. In certain places, the meningeal layer of the dura folds inward to separate major parts of the brain. i. The falx cerebri extends into the longitudinal fissure as a wall between the cerebral hemispheres. ii. The tentorium cerebelli is like a roof over the posterior cranial fossa and separates the cerebellum from the cerebrum. iii. The falx cerebelli partially separates the right and left halves of the cerebellum. 3. The arachnoid mater and pia mater are similar to those of the spinal cord. a. The arachnoid mater is a transparent membrane over the brain surface. (Fig. 14.1c) i. The subarachnoid space separates it from the pia mater below. ii. In some places a subdural space separates it from the dura above. b. The pia mater is a very thin, delicate membrane that follows all contours of the brain and sulci. Insight 14.1 Meningitis B. The brain has four internal chambers called ventricles that are filled with cerebrospinal fluid. (pp. 521–524) (Fig. 14.6) Saladin Outline Ch.14 Page 4 1. The largest and most rostral are the lateral ventricles, which form an arc in each cerebral hemisphere. 2. The lateral ventricles connect to the third ventricle, a median space inferior to the corpus callosum, via the interventricular foramina. 3. A canal called the cerebral aqueduct leads from the third ventricle to the fourth ventricle, a triangular chamber between the pons and cerebellum. 4. The fourth ventricle narrows caudally to form the central canal that extends through the medulla oblongata into the spinal cord. 5. Each ventricle has a mass of blood capillaries on the floor or wall called a choroids plexus. a. Ependyma is a type of neuroglia that resembles cuboidal epithelium. b. It lines the ventricles and canals, covers the choroids plexuses, and produces cerebrospinal fluid. 6. Cerebrospinal fluid (CSF) is a clear, colorless liquid that fills the ventricles and canals of the CNS and bathes its external surface. a. The brain produces about 500 mL of CSF per day, but it is constantly reabsorbed and only 100 to 160 mL is normally present at one time. b. CSF production begins with filtration of blood plasma through the brain’s capillaries. i. Ependymal cells modify this filtrate so that CSF has more sodium and chloride, but less potassium, calcium, and glucose and very little protein. b. CSF is circulated through the CNS by its own pressure, by the beating of cilia on the ependymal cells, and by rhythmic pulsations of the brain produced by the heartbeat. i. CSF secreted in the lateral ventricles flows through the interventricular foramina into the third ventricle and then down the cerebral aqueduct to the fourth ventricle. (Fig. 14.7) ii. The third and fourth ventricles add more CSF. c. A small amount of CSF fills the central canal of the spinal cord, but all of it escapes through three pores in the walls of the fourth ventricle: a median aperture and two lateral apertures. i. These apertures lead into the subarachnoid space. ii. CSF is reabsorbed in this space by the arachnoid villi. 7. CSF serves three purposes. a. Buoyancy. The brain and CSF are similar in density; this buoyancy allows the brain to attain considerable size without being impaired by its own weight. Saladin Outline Ch.14 Page 5 b. Protection. CSF helps prevent the brain from striking the cranium when the head is jolted; however, severe jolts may still be damaging, as in shaken baby syndrome and concussions from car accidents, boxing, etc. c. Chemical stability. The flow of CSF rinses metabolic wastes away and homeostatically regulates the brain’s chemical environment. Insight 14.2 Hydrocephalus C. The blood supply to the nervous system is critically important, and the brain barrier system protects the brain from harmful agents in the blood. (p. 524) 1. The brain is only 2% of the adult weight, but it receives 15% of the blood and consumes 20% of the oxygen and glucose of the body. a. A 10-second interruption in blood flow can cause loss of consciousness; 1 to 2 minutes, impairment of function; and 4 minutes irreversible brain damage. 2. The brain barrier system regulates what substances can get from the bloodstream into the tissue fluid of the brain. a. The blood capillaries through the brain tissue is one point of entry, and it is protected by the blood–brain barrier (BBB) consisting of tight junctions between endothelial cells that form the capillary walls. i. During development, astrocytes induce development of the tight junctions in these endothelial cells. ii. Anything leaving the blood must therefore pass through the cells and not between them. b. The choriod plexuses are another point of entry, and this is protected by the blood–CSF barrier formed by tight junctions between ependymal cells. i. Tight junctions are absent from ependymal cells elsewhere, allowing exchange between brain and CSF. 2. The BBS is highly permeable to water, glucose, and lipid-soluble substances such as oxygen, carbon dioxide, alcohol, caffeine, nicotine, and anesthetics; it is slightly permeable to sodium, potassium, chloride, and waste produces urea and creatinine. a. The BBS is an obstacle to delivery of medications such as antibiotics and cancer drugs. b. Trauma and inflammation sometimes damage the BBS, allowing pathogens to enter the brain tissue. c. In the third and fourth ventricles, circumventricular organs (CVOs) lack the barrier, and the blood has direct access to the brain. i. CVOs allow the brain to monitor and respond to blood variables, but they also afford a route of invasion by HIV. III. The Hindbrain and Midbrain (pp. 524–531) Saladin Outline Ch.14 Page 6 A. Beginning caudally, the medulla oblongata of the adult hindbrain differentiates from the embryonic myelencephalon. (pp. 524–525) 1. The medulla begins at the foramen magnum and extends about 3 cm rostrally, ending at a groove between the medulla and pons. (Figs. 14.2, 14.8) a. Externally, the anterior surface has a pair of ridges called the pyramids, which are wider at the rostral end, taper caudally, and are separated by the anterior median fissure. b. Lateral to each pyramid is a bulge called the olive. c. Posteriorly, the gracile fasciculi and cuneate fasciculi of the spinal cord continue as two pairs of ridges on the medulla. 2. All nerve fibers connecting the brain to the spinal cord pass through the medulla. a. The ascending fibers include first-order sensory fibers of the two fasciculi, which end in the gracile and cuneate nuclei. (Fig. 14.9c) i. These nuclei synapse with second-order fibers that decussate and form the medial lemniscus on each side. ii. The second-order fibers rise to the thalamus, synapsing with thirdorder fibers that continue to the cerebral cortex. iii. Near the cuneate nucleus, a continuation of the spinal posterior spinocerebellar tract carries sensory signals to the cerebellum. b. The largest group of descending fibers is the pair of corticospinal tracts filling the pyramids on the anterior surface. i. These carry motor signals from the cerebral cortex to the spinal cord, ultimately to stimulate skeletal muscles. ii. About 90% of these fibers cross over at the pyramidal decussation near the caudal end of the pyramids; muscles below the neck are therefore controlled contralaterally. (Fig. 14.8a) iii. A smaller bundle of descending fibers, the tectospinal tract, originates in the midbrain, passes through the medulla, and controls muscles of the neck. 3. The medulla contains neural networks involved in many sensory and motor functions. a. Sensory functions include the sense of touch, pressure, temperature, taste and pain b. Motor functions include chewing, salivation, swallowing, gagging, vomiting, respiration, speech, coughing, sneezing, sweating, cardiovascular and gastrointestinal control, and head, neck, and shoulder movements. Saladin Outline Ch.14 Page 7 4. Signals enter and leave the medulla not only via the spinal cord but also through four pairs of cranial nerves that begin or end there: glossopharyngeal (CN IX), vagus, (CN X), accessory (CN XI), and hypoglossale (CN XII) nerves. (Table 14.1) a. The trigeminal nerve (CN V), belongs to the pons but has parts extending into the medulla. 5. The wavy inferior olivary nucleus is a major relay center. 6. The reticular formation is a loose network of nuclei extending throughout the medulla, pons, and midbrain. a. In the medulla, it includes a cardiac center, a vasomotor center, two respiratory centers, and other nuclei involved in motor functions. B. The embryonic metencephalon develops into two structures, the pons and the cerebellum; the pons is about 2.5 cm long and appears as a broad anterior bulge rostral to the medulla. (pp. 525– 527) (Figs. 14.2, 14.8) 1. Posteriorly, the pons consists of two pairs of thick stalks called cerebellar peduncles that connect the pons and midbrain. (Fig. 14.9b) 2. The pons has continuations of the reticular formation, medial lemniscus, and tectospinal tract, as well as extensions from the spinal cord of the anterolateral system and anterior spinocerebellar tract. 3. The anterior pons has tracts of white matter, including transverse fascicles that decussate and connect the cerebellar hemispheres, and longitudinal fascicles that carry sensory and motor signals. (Fig. 14.9b) 4. Cranial nerves V to VIII begin or end in the pons; their functions include sensory roles and motor roles. (Table 14.1) 5. The reticular formation in the pons contains additional nuclei concerned with sleep, respiration, and posture. C. The embryonic mesencephalon becomes just one adult brain structure, the midbrain; it connects the hindbrain and forebrain. (Figs. 14.2, 14.8) (p. 528) 1. The midbrain contains the cerebral aqueduct, continuations of the medial lemniscus and reticular formation, and motor nuclei for the oculomotor (CN III) and trochlear (CN IV) nerves that control eye movements. 2. The part of the midbrain posterior to the cerebral aqueduct is the rooflike tectum, which exhibits four bulges, the corpora quadrigemina. a. The upper pair, the superior colliculi, controls vision and eye-related functions (visual tracking, blinking, focusing, etc.). b. The lower pair, the inferior colliculi, receives signals from the inner ear and relays them to other parts of the brain, especially the thalamus. Saladin Outline Ch.14 Page 8 3. Anterior to the cerebral aqueduct, the midbrain consists mainly of the two cerebral peduncles that anchor the cerebrum to the brain stem; each peduncle has three main components: tegmentum, substantia nigra, and cerebral crus. a. The tegmentum is dominated by the red nucleus, whose fibers form the rubrospinal tract in most mammals, but in humans go to and from the cerebellum to collaborate in fine motor control. b. The substantia nigra is a nucleus pigmented with melanin; it is a motor center that relays inhibitory signals to the thalamus and basal nuclei. i. Degeneration of neurons in the substantia nigra is responsible for the tremors of Parkinson disease. c. The cerebral crus is a bundle of nerve fibers connecting the cerebrum to the pons and carrying corticospinal nerve tracts. 4. Surrounding the cerebral aqueduct is the central (periaqueductal) gray matter, an arrowhead-shaped body; it is involved with the reticulospinal tracts in controlling awareness of pain. D. The reticular formation is a web of gray matter that runs vertically through all levels of the brain stem. (Fig. 14.9) (pp. 528–529) 1. The reticular formation occupies much of the space between the white fiber tracts and the brainstem nuclei, and connects with many areas of the cerebrum. (Fig. 14.10) 2. It consists of more than 100 small neural networks that include five functions. a. Somatic motor control. Some motor neurons of the cerebral cortex send axons to reticular formation nuclei, which give rise to the reticulospinal tracts of the spinal cord; these adjust muscle tone, balance, and posture during movement i. The reticular formation also relays signals from the eyes and ears to the cerebellum so that this information can be integrated with motor coordination. ii. Other motor nuclei include gaze centers and central pattern generators. b. Cardiovascular control. The reticular formation includes the cardiac and vasomotor centers of the medulla oblongata. c. Pain modulation. The reticular formation is one route for pain signals to the cerebral cortex; is also is the origin of the descending analgesic pathways that block pain signal transmission. d. Sleep and consciousness. The reticular formation plays a central role in states such as alertness and sleep; injury to the reticular formation can result in irreversible coma. Saladin Outline Ch.14 Page 9 e. Habituation. This process allows the brain to ignore repetitive, inconsequential stimuli via the reticular activating system or extrathalamiccortical modulatory system. E. The cerebellum is the largest part of the hindbrain and consists of right and left cerebellar hemispheres connected by a wormlike bridge, the vermis. (pp. 529–530) (Fig. 14.11) 1. Each hemisphere exhibits parallel folds called folia separated by shallow sulci.. 2. The cerebellum has a surface cortex of gray matter and a deeper layer of white matter. a. The white matter exhibits a fernlike pattern called the arbor vitae. b. Each hemisphere has four masses of gray matter called deep nuclei embedded in the white matter. c. All input to the cerebellum goes to the cortex and all output comes from the deep nuclei. 3. The cerebellum is 10% of the brain’s mass but has 60% of the surface area of the cerebral cortex and contains more than half of all brain neurons. a. Its tiny granule cells are the most abundant type of neuron in the brain. b. The unusually large Purkinje cells are the most distinctive; they have a tremendous profusion of dendrites compressed into a single plane like a flat tree. (Fig. 12.5) 4. The cerebellum is connected to the brain stem by three pairs of stalks, the cerebellar peduncles. (Fig. 14.8b) a. A pair of inferior peduncles connect to the medulla oblongata. b. A pair of middle peduncles connect to the pons. c. A pair of superior peduncles connect to the midbrain. 5. Most spinal input enters by way of the inferior peduncles; most input from the rest of the brain by way of the middle peduncles; and most output travels by way of the superior peduncles. 6. Cerebellar lesions cause deficits in coordination and locomotor ability, and also in sensory, linguistic, emotional, and other nonmotor functions. a. The cerebellum is highly active in tactile exploration and in spatial perception. b. The cerebellum is a timekeeping center involved in rhythm and in prediction of trajectories of moving objects. c. Cerebellar lesions may impair a person’s ability to judge differences in pitch of sounds, and language input and output may be affected. d. People with cerebellar lesions also have difficulty planning and scheduling tasks, tend to overreact, and have difficulty with impulse control. i. Many children with ADHD have abnormally small cerebellums. IV. The Forebrain (pp. 531–537) Saladin Outline Ch.14 Page 10 A. The forebrain consists of the diencephalon, which is the most rostral part of the brainstem, and the telencephalon, which develops chiefly into the cerebrum. (p. 531) B. The diencephalon, which encloses the third ventricle, has three major derivatives; the thalamus, hypothalamus, and epithalamus. 1. Each side of the brain has a thalamus, an ovoid mass at the superior end of the brainstem beneath the cerebral hemisphere. (Figs. 14.6c, 14.8, 14.16) a. The thalami constitute about four-fifths of the diencephalon, protruding medially into the third ventricle and laterally into the lateral ventricles. b. In about 70% of people, the thalami are joined medially by a narrow intermediate mass. c. The thalamus is composed of 23 nuclei classed into five main functional groups: anterior, posterior, medial, lateral, and ventral. (Fig. 14.12a) d. The thalamus is the “gateway to the cerebral cortex” in that nearly all input passes through synapses in the thalamic nuclei. e. The thalamus plays a key role in motor control by relaying signals from the cerebellum to the cerebrum. f. It provides feedback loops between the cerebral cortex and the deep cerebral motor centers (the basal nuclei). g. The thalamus is involved in the memory and emotional functions of the limbic system. 2. The hypothalamus forms part of the walls and floor of the third ventricle and extends anteriorly to the optic chiasm and posteriorly to the mammillary bodies. (Fig. 14.2) a. Each mamillary body contains three to four mammillary nuclei that relay signals from the limbic system to the thalamus. b. The pituitary glad is attached to the hypothalamus by a stalk (infundibulum) between the optic chiasm and mammillary bodies. c. The hypothalamus is the major control center of the autonomic nervous system and endocrine system and is concerned with a variety of visceral functions. (Fig. 14.12b) i. Hormone secretion. Hormones secreted by the hypothalamus control the anterior pituitary gland to regulate growth, metabolism, reproduction, and stress response; the hypothalamus also produces hormones that are stored in the posterior pituitary that have to do with labor contraction, lactation, and water balance. ii. Autonomic effects. The hypothalamus is an integrating center for the autonomic nervous system and influences heart rate, blood pressure, and other visceral functions. Saladin Outline Ch.14 Page 11 iii. Thermoregulation. The hypothalamic thermostat, a collection of neurons mainly in the preoptic nucleus, monitor body temperature and adjust it. iv. Food and water intake. The hunger and satiety centers of the hypothalamus monitor blood glucose levels, and osmoreceptors monitor the salt concentration of the blood; these stimulate behavioral and hormonal changes. v. Sleep and circadian rhythms. The caudal part of the hypothalamus is part of the reticular formation and regulates the rhythm of sleep and waking; the suprachiasmatic nucleus superior to the optic chiasm controls circadian rhythms. vi. Memory. The mammillary nuclei lie in the pathway of signals from the hippocampus, a memory center, to the thalamus; lesions to the mammillary nuclei cause memory deficits. vii. Emotional behavior. Hypothalamic centers are involved in anger, aggression, fear, pleasure, sexual drive, copulation, and orgasm. C. The epithalamus is a very small mass of tissue composed of the pineal gland, the habenula that serves as a relay from the limbic system to midbrain, and a thin roof over the third ventricle. (p. 533) (Fig. 14.2a) D. The cerebrum develops from the embryonic telencephalon; it is the largest and most conspicuous part of the human brain. (pp. 533–537) 1. In terms of gross anatomy, the cerebrum has two cerebral hemispheres separated by the longitudinal fissure but connected by the corpus callosum. a. The conspicuous gyri of each hemisphere are separated by grooves called sulci; the folding into gyri allows a greater amount of cortex to fit into the cranial cavity. b. Some gyri have consistent anatomy while others vary between individuals. c. Certain prominent sulci divide each hemisphere into five distinct lobes. (Fig. 14.13) i. The front lobe lies behind the frontal bone, superior to the eyes, and extends caudally to the central sulcus; it is involved in voluntary motor functions and higher mental functions. ii. The parietal lobe forms the uppermost part of the brain, underlying the parietal bone, and extends caudally to the parieto-occipital sulcus; it is involved in general sense, taste, and some visual processing. (Fig. 14.2) Saladin Outline Ch.14 Page 12 iii. The occipital lobe is at the rear of the head, caudal to the parietooccipital sulcus and underlying the occipital bone; it is the principle visual center. iv. The temporal lobe is a lateral, horizontal lobe deep to the temporal bone and separated from fthe parietal lobe by a deep lateral sulcus; it is concerned with hearing, smell, learning, memory, and some aspects of vision and emotion. v. The insula is a small mass of cortex deep to the lateral sulcus and only visible by retracting or cutting away some of the cerebrum; it has roles in language, sense of taste, and integrating visceral sensory information. (Figs. 14.1c, 14.6c, 14.13) 2. White matter makes up most of the volume of the cerebrum and is composed of glia and myelinated nerve fibers organized into three kinds of tracts. a. Projection tracts extend vertically between higher and lower brain and spinal cord centers. i. For example, corticospinal tracts carry motor signals from the cerebrum to the brain stem and spinal cord. ii. Superior to the brain stem, the projection tracts form a broad, dense sheet, the internal capsule, and the radiate in a fanlike array, the corona radiate, to specific cortical centers. b. Commissural tracts cross from one hemisphere to the other through commisures. i. Most pass through the corpus callosum, which forms the floor of the longitudinal fissure. ii. A few pass through the much smaller anterior and posterior commissures. c. Association tracts connect different regions within the same hemisphere. i. Long association fibers connect different lobes within the same hemisphere, whereas short association fibers connect different gyri within a single lobe. ii. Among other roles, association tracts link perceptual and memory centers. 3. Neural integration is carried out in the cerebral gray matter, found in the cerebral cortex, basal nuclei, and limbic system. 4. The cerebral cortex is a layer covering the surface of the hemispheres, constituting 40% of the mass of the brain and containing 14 to 16 billion neurons. (Fig. 14.6) Saladin Outline Ch.14 Page 13 a. The cerebral cortex contains two principle types of neurons, stellate cells and pyramidal cells. (Fig. 14.15) b. Stellate cells have spheroidal somas with dendrites projecting short distances in all directions; they are concerned with sensory input and processing information locally. c. Pyramidal cells are tall and conical with their apex pointing toward the brain surface. i. They have a thick dendrite with many branches, and small knobby dendritic spines. ii. The base gives rise to horizontally oriented dendrites and an axons that passes into the white matter. iii. Pyramidal cells include the output neurons of the cerebrum and are the only neurons whose fibers leave the cortex and connect with other parts of the CNS. d. 90% of the human cerebral cortex is a six-layered tissue called neocortex from its recent evolutionary origin about 60 million years ago. (Fig. 14.15) i. Layer thickness, composition, and connections vary in different regions. ii. All axons that leave the cortex and enter the white matter arise from layers III, V, and VI. e. Some regions of the cerebral cortex have fewer than six layers. i. The earliest type of cortex to appear was the paleocortex, limited in humans to part of the insula and certain areas of the temporal lobe concerned with smell. ii. The next to evolve was the archicortex, found in the human hippocampus. iii. The neocortex was the last to evolve. 5. The basal nuclei are masses of cerebral gray matter buried in the white matter, lateral to the thalamus. (Fig. 14.16) a. They are often called basal ganglia, although ganglion is best restricted to clusters of neurons outside the CNS. b. Three brain centers are classified as basal nuclei: the caudate nucleus, putamen, and globus pallidus. i. The putamen and globus pallidus are collectively called the lentiform nucleus. ii. The putamen and caudate nucleus are collectively called the corpus striatum. Saladin Outline Ch.14 Page 14 c. The basal nuclei receive input from the substantia nigra of the midbrain and motor areas of the cerebral cortex. 6. The limbic system is an important center of emotion and learning and consists of a ring of structures on the medial side of the cerebral hemisphere, encircling the corpus callosum and thalamus. (Fig. 14.17) a. Its most prominent components are the cingulate gyrus that arches over the corpus callosum; the hippocampus, in the medial temporal lobe; and the amygdala, rostral to the hippocampus in the temporal lobe. b. Other components include the mammillary nuclei and other hypothalamic nuclei; some thalamic nuclei; parts of the basal nuclei; and parts of the frontal cortex. c. Limbic system components are interconnected through a complex loop of fiber tracts allowing for feedback; the structures are bilaterally paired in each hemisphere. d. The limbic system has significant roles in emotion and memory and contains structures for both gratification and aversion. i. Gratification centers dominate some structures, such as the nucleus accumbens, while aversion centers dominate others, such as the amygdala. V. Integrative Functions of the Brain (pp. 538–549) A. Higher brain functions such as sleep, memory, cognition, emotion, sensation, motor control, and language are associated with the cerebral cortex, but not exclusively; they involved interactions between the cerebral cortex and other regions such as the basal nuclei, brainstem, and cerebellum. (p. 538) B. The brain’s surface electrical activity, or brain waves, can be recorded as an electroencephalogram (EEG), which can be useful in studying both normal and abnormal brain functions. (pp. 538–539) (Fig. 14.18) 1. Four types of brain waves can be distinguished based on differences in amplitude (mV) and frequency (Hz): Alpha, beta, theta, and delta waves. 2. Alpha (α) waves have a frequency of 8 to 13 Hz and are recorded especially in the parieto-occipital area. a. They dominate the EEG when a person is awake and resting with the mind wandering. b. They are suppressed during sensory stimulation and mental tasks, and are absent during sleep. 3. Beta (β) waves have a frequency of 14 to 30 Hz and occur in the frontal to parietal region. Saladin Outline Ch.14 Page 15 a. They are accentuated during mental activity and sensory stimulation. 4. Theta (θ) waves have a frequency of 4 to 7 Hz. a. They are normal in children and in drowsy or sleeping adults, but a predominance in awake adults suggests emotional stress or brain disorders. 5. Delta (δ) waves are high-amplitude “slow waves” with a frequency of less than 3.5 Hz. a. Infants exhibit delta waves when awake, and adults exhibit them in deep sleep. b. A predominance of delta waves in awake adults indicates serious brain damage. C. Sleep is one of many bodily functions that occur in cycles called circadian rhythms. (pp. 539– 540) 1. Sleep can be defined as a temporary state of unconsciousness from which one can awaken when stimulated. a. It is characterized by a stereotyped posture (lying down with eyes closed) and inhibition of muscular activity (sleep paralysis). b. It resembles coma and hibernation, except that individuals cannot be aroused from these states by sensory stimulation. 2. Sleep occurs in four distinct stages recognizable from changes in EEG. (Fig. 14.19a) a. Stage 1 includes feeling drowsy, closing the eyes, and starting to relax; the EEG is dominated by alpha waves. b. Stage 2 is light sleep during which the EEG declines in frequency but increases in amplitude, occasionally exhibiting sleep spindles from interactions between thalamus and cerebral cortex. c. Stage 3 is moderate to deep sleep, typically beginning about 20 minutes after stage 1. Theta and delta waves appear and vital signs fall. d. Stage 4 is also called slow-wave sleep (SWS) because the EEG is dominated by delta waves; vital signs are at their lowest levels and a person is difficult to awaken. 3. About five times a night, a sleeper backtracks to stage 2 and exhibits rapid eye movement (REM) sleep. (Fig. 14.19b) a. The eyes oscillate back and forth as though watching a movie. b. It is also called paradoxical sleep because the EEG resembles the waking state, yet the sleeper is harder to arouse than at any other stage. c. Vital signs increase, and sleep paralysis is especially strong during REM sleep. 4. Dreams occur during both REM and non-REM sleep, but REM dreams tend to be longer, more vivid, and more emotional. Saladin Outline Ch.14 Page 16 a. The parasympathetic nervous system is very active during REM sleep, causing constriction of the pupils and erection of the penis or clitoris. b. In men, penile erection accompanies 80% to 95% of REM sleep but is seldom associated with sexual dream content. 5. The cycle of sleep and waking is controlled by complex interactions between cerebral cortex, thalamus, hypothalamus, and reticular formation. a. Nuclei in the upper reticular formation near the junction of the pons and midbrain induce arousal, whereas nuclei below the pons induce sleep. b. Sleep is also induced by a ventrolateral preoptic nucleus in the hypothalamus, which inhibits arousal neurons in the upper reticular formation. c. The suprachiasmatic nucleus (SCN), just above the optic chiasm, is another important control center for sleep. i. Some nerve fibers from the eyes go to the SCN, which uses the input to synchronize body rhythms with the external rhythm of night and day. ii. The SCN does not induce sleep or waking, but regulates the time of day that a person sleeps; destruction of the SCN in an animal results in sleeping at random times although for the same number of hours per day. 6. Scientists know little about the purposes of sleep and dreaming, except that sleep deprivation can lead to death. a. One hypothesis is that energy sources such as glycogen and ATP are replenished during sleep. b. Another idea is that sleep may have evolved to motivate animals to find a safe place and remain inactive during dangerous times of day. c. Some researchers suggest that REM sleep is a period in which the brain either consolidates and strengthens memories or purges superfluous information from memory. D. Cognition is the range of mental processes by which we acquire and use knowledge. (p. 541) 1. Cognitive functions are widely distributed over regions of the cerebral cortex called association areas, which make up 75% of brain tissue. 2. Much of what we know has come from studies of patients with brain lesions; more recently PET scans and fMRI scans have yielded more sophisticated insights. a. Parietal lobe lesions can cause people to become unaware of objects, or even their own limbs, on the opposite side of the body (contralateral neglect syndrome). Saladin Outline Ch.14 Page 17 b. Temporal lobe lesions often result in agnosia, the inability to recognize, identify, and name familiar objects; prosopagnosia is the inability to remember familiar faces. c. Frontal lobe lesions affect qualities we think of as personality and responses to stimuli. i. The prefrontal cortex (frontal association area) is the most rostral part of the frontal lobe and is well developed only in primates, particularly humans. ii. Lesions here may produce personality disorders and socially inappropriate behaviors. E. Memory is one of the major cognitive functions. (pp. 541–542) 1. Information management by the brain entails learning, memory proper, and forgetting. a. Forgetting is important in that people with pathological inability to forget trivial information have difficulty in reading comprehension and separation of important information from nonimportant. 2. Brain-injured people may be unable to store new information (anterograde amnesia) or recall things known before the injury (retrograde amnesia) a. Amnesia refers to defects in declarative memory (recounting) not procedural memory (actions). 3. The hippocampus of the limbic system is an important memory forming center (Fig. 14.17) a. The hippocampus does not store memories, but organizes sensory and cognitive experiences into a unified long-term memory. b. It learns from sensory input during an experience but is thought to play the memory repeatedly to the cerebral cortex, a process called memory consolidation. c. Long-term memories are stored in different cortical areas: vocabulary in the superior temporal lobe, plans and social roles in the prefrontal cortex. d. Lesions of the hippocampus can cause profound anterograde amnesia. 4. Other parts of the brain involved in memory include the cerebellum and the amygdala. Insight 14.3 The Seat of Personality—A Lesson from an Accidental Lobotomy (Fig. 14.20) F. Emotional feelings and memories are not exclusively cerebral functions but result from an interaction between areas of the prefrontal cortex and diencephalon. (pp. 542–543) 1. Emotional control centers of the brain have been identified by studying people with brain lesions, but interpretation of results is controversial. Saladin Outline Ch.14 Page 18 2. The prefrontal cortex is the seat of judgment, intent, and control over expression of emotions, but emotions and emotional memories arise from deeper regions, expecially the hypothalamus and amygdala. 3. The amygdala is a major component of the limbic system and received processed information from the general senses and from vision, hearing, taste, and smell. a. It is especially important in the sense of fear, but also plays roles in food intake, sexual behavior, and novel stimuli. b. Output from the amygdala goes in two directions of interest: (1) to the hypothalamus and lower brainstem, where it influences somatic and visceral motor systems; (2) to areas of the prefrontal cortex that mediate conscious control of emotions. 4. Many important aspects of personality, such as expressions of anger, fear, pleasure, pain, love, sexuality, and affection, as well as aspects of learning, memory, and motivation depend on an intact, functional amygdala and hypothalamus. 5. Much of human behavior is shaped by learned associations between stimuli, our responses, and the results. a. Certain nuclei in the hypothalamus are involved in feelings of reward and punishment; one which has been studied in animals is the median forebrain bundle (MFB). i. Mammals that can press a pedal to cause electrical stimulation of the MFB will do so repeatedly even to the point of neglecting food and water. ii. Humans with incurable schizophrenia, pain, or epilepsy with electrode implants that stimulate the MFB also will press a button to cause stimulation, but do not report feelings of joy or ecstasy—rather a relief from tension, a relaxed feeling, or no feeling at all. G. Much of the cerebrum is concerned with the senses: most of the cortex of the insula and of the parietal, occipital, and temporal lobes. (pp. 543–544) 1. Regions called primary sensory cortex are sites where sensory input is first received and one becomes conscious of a stimulus. 2. Adjacent to these are association areas where the sensory input is interpreted. a. Some association areas are multimodal, receiving input from multiple senses; an example is the orbitofrontal cortex, which receives taste, smell, and visual input to form an impression of a food. 3. The special senses are limited to the head: vision, hearing, equilibrium, taste, and smell. (Fig. 14.21) Saladin Outline Ch.14 Page 19 a. Vision. Visual signals are received by the primary visual cortex in the posterior region of the occipital lobe. i. The visual cortex is bordered anteriorly by the visual association area that makes up the remainder of the occipital lobe, some of the posterior parietal lobe, and much of the inferior temporal lobe. b. Hearing. Auditory signals are received by the primary auditory cortex in the superior region of the temporal lobe and in the nearby insula. i. The auditory association area occupies areas of temporal lobe inferior to the primary audiotyr cortex and deep within the lateral sulcus. c. Equilibrium. Signals from the inner ear for balance and the sense of motion project mainly to the cerebellum and several brainstem nuclei concerned with head and eye movements and visceral functions. i. Some fibers, however, are routed through the thalamus to association areas in the roof of the lateral sulcus and lower end of the central sulcus, which perceive body movements and orientation in space. d. Taste and smell. i. Gustatory (taste) signals are received by the primary gustatory cortex in the inferior end of the postcentral gyrus of the parietal lobe and an anterior region of the insula. ii. Olfactory (smell) signals are received by the primary olfactory cortex in the medial surface of the temporal lobe and inferior surface of the frontal lobe. iii. The orbitofrontal cortex is a multimodal association area for both these senses. 4. The general senses (somesthetic, somatosensory, or somatic senses) are distributed over the entire body and include touch, pressure, stretch, movement, heat and cold, and pain. a. Coming from the head, such signals reach the brain via certain cranial nerves, notably the trigeminal nerve; from the rest of the body, the signals ascend sensory tracts of the spinal cord. i. Both routes decussate to the contralateral thalamus. b. The thalamus processes the input and selectively relays signals to the postcentral gyrus. (Fig. 14.22a) c. The cerebral cortex of the postcentral gyrus is called the primary somesthetic cortex. i. Adjacent to this is the somesthetic association area (Fig. 14.21) Saladin Outline Ch.14 Page 20 d. Because of the decussation, the primary somesthetic cortex is like an upsidedown sensory map of the contralateral side of the body, traditionally diagrammed as a sensory homunculus. (Fig. 14.22b) i. Receptors in the lower limb project to superior and medial parts of the gyrus, and receptors in the face project to the inferior and lateral parts. ii. Point-for-point correspondence between an area of the body and an area of th CNS is called somatotopy. iii. Relative sizes of body parts in the sensory homunculus correspond to the amount of innervation and sensitivity of each part. H. Motor control involves first the intention to contract a skeletal muscle, which begins in the motor association (premotor) area of the frontal lobes. (pp. 544–546) (Fig. 14.21) 1. The program for action is then transmitted from the premotor area to neurons of the precentral gyrus (primary motor area), the most posterior gyrus of the frontal lobe, immediately anterior to the central sulcus. (Fig. 14.23a) a. Neurons in the precentral gyrus send signals to the brainstem and spinal cord, which ultimately results in muscle contraction. b. The precentral gyrus, like the postcentral one, exhibits somatotopy and can be mapped as a motor homunculus. (Fig. 14.23b) i. Relative sizes of body parts in the motor homunculus correspond to the number of muscles and motor units in each part. 2. The pyramidal cells of the precentral gyrus are called upper motor neurons. a. Their fibers project caudally with about 19 million fibers ending in nuclei of the brainstem and 1 million forming the corticospinal tracts. b. Most of these fibers decussate in the lower medulla oblongata and form the lateral corticospinal tract on each side of the spinal cord. c. A smaller number of fibers pass through the medulla without decussation and form the anterior corticospinal tracts, which cross over lower in the spinal cord. 3. In the brainstem or spinal cord, fibers from the upper motor neurons synapse with lower motor neurons, the axons of which innervate the skeletal muscles. (Fig. 13.6) 4. The basal nuclei and cerebellum are other important muscle control areas. a. The basal nuclei determine the onset and cessation of intentional movements; walking; and highly practiced learned behaviors like typing or tying shoes. i. The basal nuclei lie in a feedback circuit from the cerebrum to the basal nuclei to the thalamus and back to the cerebrum. ii. Nearly all areas of cerebral cortex, except for primary visual and auditory cortices, send signals to the basal nuclei. Saladin Outline Ch.14 Page 21 iii. The basal nuclei process these signals and output to the thalamus, which relays signals back to the cerebral cortex, notably to motor areas. iv. Lesions of basal nuclei cause dyskinesias, such as seen in the rigid movements of Parkinson disease and the exaggerated movements of Huntington disease. b. The cerebellum is important in motor coordination, aids in learning motor skills, maintains muscle tone and posture, coordinates eye and body movements, and the motions of different joints. i. Through the middle peduncles, the cerebellum receives information from the upper motor neurons of the cerebrum about movement intentions and information about body movement from the eyes and inner ears. ii. Through the inferior peduncles, it receives information from proprioceptors in the muscle and joints about performance. (Fig. 14.24) iii. The Purkinje cells compare the two, and if there is a discrepancy, they signal the deep cerebellar nuclei, which issue signals to the thalamus and lower brainstem and ultimately the motor association area of the cerebrum and tracts of the spinal cord. (Fig. 14.24) iv. Output from these areas correct the muscle performance. v. Lesions of the cerebellum can results in a clumsy, awkward gait (ataxia). I. Language includes several abilities—reading, writing, speaking, and understanding words— assigned to different regions of the cerebral cortex. (pp. 546–548) (Fig. 14.25) 1. The Wernicke area is responsible for the recognition of spoken and written language. a. It is a multimodal association area that lies posterior to the lateral sulcus, usually in the left hemisphere, at the crossroad between visual, auditory, and somesthetic areas. 2. The angular gyrus, part of the pariental lobe caudal and superior to the Wernicke area, is important in the ability to read and write. 3. When we intend to speak, the Wernicke area formulates phrases and transmits a plan to the Broca area, located in the inferior prefrontal cortex in the same hemisphere. a. PET scans show a rise in metabolic activity of the Broca area as we prepare to speak (Fig. 14.40) b. The Broca area generates a motor program from muscles in the larynx, tongue, cheeks, and lips to produce speech and transmits it to the primary motor cortex. Saladin Outline Ch.14 Page 22 4. The emotional aspect of language is controlled by regions in the opposite hemisphere that mirror the Wernicke and Broca areas. a. The affective language area lies opposite the Broca area; lesions to this area results in flat, emotionless speech (aprosody). b. The cortex opposite Wernicke’s area is concernd with recognizing the emotional content of another person’s speech; lesions here can result in problems understanding speech intent, such as a joke. 5. Aphasia is any language deficit resulting from lesions in the hemisphere, usually the left, containing the Wernicke and Broca areas. a. Nonfluent (Broca) aphasia results in slow speech, difficulty in chooswing words, or use of words that only approximate the correct word. b. Fluent (Wernicke) aphasia results in a person speaking normally and sometimes excessively, but using jargon and invented words that make little sense. c. In anomic aphasia, a person can speak noirmally and understand speech, but cannot identify written words or pictures. J. The two cerebral hemispheres look roughly identical but have a number of differences in function, a difference termed cerebral lateralization. (p. 548) 1. One hemisphere, usually the left, is specialized for spoken and written language and for sequential and analytical reasoning; it is termed the categorical hemisphere. 2. The other hemisphere perceives information in an integrated, holistic way and is the seat of imagination, insight, musical/artistic skills, spatial relationships and patterns, and comparisons of special senses; it is termed the representational hemisphere. 3. Cerebral lateralization is highly correlated with handedness. a. The left hemisphere is categorical in 96% of right-handed people, and the right hemisphere in 3%. b. Among left-handed people, the right hemisphere is categorical in 15% and the left in 70%; in the remaining 15% neither hemisphere is distinctly specialized. 4. Lateralization develops with age, and in children, one hemisphere can often take over the functions of the other if it is damaged. 5. Adult males exhibit more lateralization than females and suffer more functional loss of one hemisphere is damaged. VI. The Cranial Nerves (pp. 549–560) A. The brain communicates via 12 pairs of cranial nerves in addition to the major input and output via the spinal cord. (p. 549) B. The cranial nerves are numbered I to XII starting with the most rostral pair, and each nerve also has a descriptive name. (p. 549) (Fig. 14.27) Saladin Outline Ch.14 Page 23 C. In terms of cranial nerve pathways, most motor fibers of these nerves begin in nuclei of the brainstem and lead to glands and muscles. (p. 549) 1. Cranial nerve sensory fibers begin in receptors located mainly in the head and neck and lead mainly to the brainstem. 2. Sensory fibers for proprioception begin in muscles innervated by motor fibers of the cranial nerves, but they often travel to the brain in a different nerve than the one supplying motor innervation. 3. Most cranial nerves carry fibers between the brain stem and ipsilateral receptors and effectors; the exceptions are the optic nerve (II), where have the fibers decussate, and the trochlear nerve (IV) in which all efferent fibers lead contralaterally. D. Cranial nerves are traditionally classified as sensory (I, II, and VIII), motor (III, IV, VI, XI, and XII), or mixed (V, VII, IX, and X), but in reality, only CN I and CN II (smell and vision) are purely sensory. (p. 550) 1. Other sensory cranial nerves contain both afferent and efferent fibers and therefore are mixed. 2. Those traditionally classified as motor not only stimulate muscle but also contain afferent fibers of proprioception. 3. CN VIII, hearing and equilibrium, is traditionally classified as sensoyr but also has motor fibers that return signals to the inner ear for fine tuning. 4. The mixed nerves have sensory functions quite unrelated to motor functions, such as CN VII (facial nerve) has a sensory role in taste and a motor roll in facial expression. E. The cranial nerves are described individually below. (pp. 550–559) (Table 14.1) 1. The olfactory nerve (CN I), the sensory nerve for the sense of smell, consists of several separate fascicles that pass independently through the cribiform plate of the ethmoid bone; these fascicles are severed when the brain is removed from the skull. (Fig. 14.28) a. Its origin is the olfactory mucosa in the nasal cavity. b. Its termination is at the olfactory bulbs on each side. c. If damaged, the sense of smell is impaired; it can be tested by determining whether a patient can sense aromatic substances. 2. The optic nerve (CN II), the sensory nerve for vision, passes out of the cranium via the optic foramen. (Fig. 14.29) a. Its origin is the retina. b. Its termination is in the thalamus and midbrain. c. If damaged, blindness occurs in part or all of the visual field; it can be tested by inspecting the retina and testing peripheral vision and visual acuity. Saladin Outline Ch.14 Page 24 3. The oculomotor nerve (CN III), predominantly a motor nerve, controls muscles that move the eyeball up, down, and medially, as well as those that control the iris, lens, and upper eyelid; it passes out of the cranium via the superior orbital fissure. (Fig. 14.30) a. Its origin is the midbrain. b. Its termination is in somatic fibers to muscles of the eye, with autonomic fibers entering the eyeball to muscles of the iris and lens. c. If the nerve is damaged, a patient may have a drooping eyelid, dilated pupil, inability to move the eye in some directions, tendency of eye to move laterally at rest, double vision, and/or difficulty focusing; test by looking for difference in pupil size, response to light, and ability to track moving objects. 4. The trochlear nerve (CN IV), predominantly a motor nerve, controls a muscle that rotates the eyeball medially and slightly depresses the eyeball when the head turns; it passes through the superior orbital fissure. (Fig. 14.31)l a. Its origin is in the midbrain. b. Its termination is the superior oblique muscle of the eye. c. If CN IV is damaged, the patient may experience double vision, an inability to rotate the eye inferolaterally, the eye pointing superolaterally, and may tend to tilt the head toward the affected side; test the ability of the eye to rotate inferolaterally. 5. The trigeminal nerve (CN V) is the largest and most important sensory nerve of the face and has three divisions. (Fig. 14.32) a. The ophthalmic division (V1) has sensory function in touch, temperature, and pain sensations from the upper face; it passes through the superior orbital fissure. i. Its origin is the superior region of face, surface of eyeball, lacrimal gland, superior nasal mucosa, and frontal and ethmoid sinuses. ii. Its termination is the pons. iii. If this nerve is damaged, sensation is lost from the upper face; it can be tested by evoking the corneal reflex (blink in response to light touch to eyeball). b. The maxillary division (V2) has the same functions as V1, but lower on the face; it passes through the foramen rotundum and infraorbital foramen. i. Its origin is the middle region of the face, the nasal mucosa, maxillary sinus, palate, and upper teeth and gums. ii. Its termination is the pons. iii. If it is damaged, sensation is lost from the middle of the face; test the sense of touch, pain, and temperature. Saladin Outline Ch.14 Page 25 c. The mandibular division (V3) is a mixed nerve, with sensory function the same as V1 and V2 but still lower on the face, and motor function in mastication; it passes through the foramen ovale. i. Its sensory origin is the inferior region of face, anterior two0-thirds of the tongue (but not taste buds), lower teeth and gums, floor of the mouth, and dura mater; its motor origin is the pons. ii. Its sensory termination is the pons; its motor termination is the anterior belly of the digastric, masseter, temporalis, mylohyoid,.and pterygoid muscles and the tensor tympani muscle of the middle ear. iii. If it is damaged, the patient may have loss of sensation and impaired chewing; assess motor functions by palpating masseter and temporalis while subject clenches teeth and test ability to move mandible side to side and open mouth. 6. The abducens nerve (CN VI), predominantly a motor nerve, controls a muscle that turns the eyeball laterally; it passes through the superior orbital fissure. (Fig. 14.33) a. Its origin is the inferior pons. b. Its termination is the lateral rectus muscle of the eye. c. If it is damaged, the patient is not able to turn the eye laterally, and at rest the eye turns medially; test for lateral eye movement. 7. The facial nerve (CN VII), a mixed nerve, has sensory function in taste and is the major motor nerve of the facial muscles. It has five prominent branches (temporal, zygomatic, buccal, mandibular, and cervical); it passes through the internal acoustic meatus and stylomastoid foramen. (Fig. 14.34) a. Its sensory origin is the taste buds of the anterior two-thirds of the tongue, and its motor origin is the pons. b. Its sensory termination is the thalamus, and its motor terminations are in the muscles of the jaw, middle ear, and facial muscles, with autonomic fibers to the salivary glands, tear glands, and nasal and palatine glands. c. If it is damaged, the patient may have an inability to control facial muscles and facial sagging due to loss of muscle tone, plus a distorted sense of taste, especially for sweet flavor; test taste with substances such as sugar, salt, vinegar, and quinine, test response of tear glands, and test subject’s ability to smile, frown, etc. 8. The vestibulocochlear nerve (CN VIII), predominantly a sensory nerve, is the nerve of hearing and equilibrium but also has motor fibers that tune the sense of hearing; it passes through the internal acoustic meatus. (Fig. 14.35) Saladin Outline Ch.14 Page 26 a. Its sensory origin is the cochlea, vestibule, and semicircular ducts of the inner ear, and its motor origin is the pons. b. Its sensory terminations consist of fibers for hearing that end in the medulla, and those for equilibrium that end at the junction of the medulla and pons; its motor termination is the outer hair cells of the cochlea of the inner ear. c. If it is damaged, the patient experiences nerve deafness, dizziness, nausea, loss of balance, and nystagmus (involuntary oscillation of eyes side to side); test for hearing, balance, and ability to walk, and check for nystagmus. 9. The glossopharyngeal nerve (CN IX) is a complex mixed nerve with numerous sensory and motor functions in the head, neck, and thoracic regions; it passes through the jugular foramen. (Fig. 14.36) a. Its sensory origins include the pharynx, middle and outer ear, posterior onethird of tongue including taste buds, and the internal carotid artery; its motor origin is in the medulla oblongata. b. Its sensory termination is the medulla oblongata; its motor terminations include the parotid gland, glands of the posterior tongue, and the stylopharyngeal muscle. c. If it is damaged, a person has impaired swallowing and loss of bitter and sour tastes; test for the gag reflex, ability to swallow and cough, and note any speech impediments; also test posterior third of tongue with sour and bitter substances. 10. The vagus nerve (CN X), a mixed nerve, has the most extensive distribution of any cranial nerve, supplying organs in the head, neck, and most viscera of the thoracic and abdominopelvic cavities; it passes through the jugular foramen. (Fig. 14.37) a. Its sensory origin includes the thoracic and abdominopelvic viscera, the root of the tongue, the pharynx, larynx, epiglottis, outer ear, and dura mater; its motor origin is the medulla oblongata. b. It sensory termination is the medulla oblongata; its motor terminations include the tongue, pharynx, larynx, lungs, heart, liver, spleen, digestive tract, kidney, and ureter. c. If it is damaged, a patient may exhibit hoarseness or loss of voice, impaired swallowing and gastrointestinal motility, and even death of both vagus nerves are damaged; test palatal movement during speech, abnormalities of swallowing, weak, hoarse voice, and absence of gag reflex. 11. The accessory nerve (CN XI), predominantly a motor nerve involved in head, neck, and shoulder actions, is unusual in that it does not arise entirely from the brain but in part from the cervical spinal cord; it passes through the jugular foramen. (Fig. 14.32) a. Its origin is the medulla oblongata and spinal cord segments C1 to C6. Saladin Outline Ch.14 Page 27 b. Its terminations are in the palate, pharynx, trapezius, and sternocleicomastoid muscles. c. if it is damaged, a patient exhibits impaired movement of head, neck, and shoulders, difficulty shrugging on affected side, and paralysis of sternocleidomastoid causing the head to turn toward injured side; test ability to rotate head and shrug shoulders. 12. The hypoglossal nerve (CN XII), predominantly a motor nerve, controls tongue movements; it passes through the hypoglossal canal. (Fig. 14.39) a. Its origin is the medulla oblongata. b. Its termination is in the intrinsic and extrinsic muscles of the tongue. c. If it is damaged, speech and swallowing are impaired, with deviation of the tongue toward injured side, with atrophy, or an inability to protrude the tongue if both left and right nerves are damaged; test movement of tongue. Cross References Additional information on topics mentioned in Chapter 14 can be found in the chapters listed below. Chapter 12: The memory process Chapter 13: Innervation of skeletal muscles Chapter 16: Control of pain awareness Chapter 16: Role of the thalamus in motor and sensory circuits Chapter 16: Nerve pathways for the special senses Chapter 17: Interaction of the hypothalamus and pituitary gland Chapter 17: The pineal gland Chapter 20: Sinuses of the brain Chapter 20: Blood vessels that supply and drain the brain Chapter 26: Temperature regulation mechanisms