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Ovid: Clinical Neuroanatomy

Authors: Snell, Richard S. Title: Clinical Neuroanatomy, 7th Edition Copyright ©2010 Lippincott Williams & Wilkins > Table of Contents > Chapter 7 – The Cerebrum Chapter 7 The Cerebrum A 23-year-old man was referred to a neurologist because of intermittent attacks of headaches, dizziness, and weakness and numbness of the left leg. On close questioning, the patient admitted that the headache was made worse by changing the position of his head. A computed tomography (CT) scan revealed a small white opaque ball at the anterior end of the third ventricle. A diagnosis of a colloid cyst of the third ventricle was made. The aggravation of the headache caused by changing the position of the head could be explained by the fact that the cyst was mobile and suspended from the choroid plexus. When the head was moved into certain positions, the ball-like cyst blocked the foramen of Monro on the right side, further raising the intracerebral pressure and increasing the hydrocephalus. The weakness and numbness of the left leg were due to pressure on the right thalamus and the tracts in the right internal capsule, produced by the slowly expanding tumor. The patient made a complete recovery after surgical excision of the tumor. P.252 Chapter Objectives

  • To introduce the student to the complexities of the forebrain
  • To understand the definition of the diencephalon and accurately localize the thalamus and hypothalamus by studying the sagittal, coronal, and horizontal sections of the brain
  • To understand the exact position of the main conduit of the ascending and descending tracts, namely the internal capsule, which is so often the site of pathologic lesions

The cerebral hemispheres are developed from the telencephalon and form the largest part of the brain. Each hemisphere has a covering of gray matter, the cortex and internal masses of gray matter, the basal nuclei, and a lateral ventricle. The basic anatomical structure of this area is described so that the student can be prepared for the complexities associated with functional localization. Subdivisions of the Cerebrum The cerebrum is the largest part of the brain, situated in the anterior and middle cranial fossae of the skull and occupying the whole concavity of the vault of the skull. It may be divided into two parts: the diencephalon, which forms the central core, and the telencephalon, which forms the cerebral hemispheres. Diencephalon The diencephalon consists of the third ventricle and the structures that form its boundaries (Figs. 7-1 and 7-2). It extends posteriorly to the point where the third ventricle becomes continuous with the cerebral aqueduct and anteriorly as far as the interventricular foramina (Fig. 7-3). Thus, the diencephalon is a midline structure with symmetrical right and left halves. Obviously, these subdivisions of the brain are made for convenience, and from a functional point of view, nerve fibers freely cross the boundaries. Gross Features The inferior surface of the diencephalon is the only area exposed to the surface in the intact brain (Fig. 7-2; see also Atlas Plate 1). It is formed by hypothalamic and other structures, which include, from anterior to posterior, the optic chiasma, with the optic tract on either side; the infundibulum, with the tuber cinereum; and the mammillary bodies. The superior surface of the diencephalon is concealed by the fornix, which is a thick bundle of fibers that originates in the hippocampus of the temporal lobe and arches posteriorly over the thalamus (Fig. 7-3; see also Atlas Plate 8) to join the mammillary body. The actual superior wall of the diencephalon is formed by the roof of the third ventricle. This consists of a layer of ependyma, which is continuous with the rest of the ependymal lining of the third ventricle. It is covered superiorly by a vascular fold of pia mater, called the tela choroidea of the third ventricle. From the roof of the third ventricle, a pair of vascular processes, the choroid plexuses of the third ventricle, project downward from the midline into the cavity of the third ventricle. The lateral surface of the diencephalon is bounded by the internal capsule of white matter and consists of nerve fibers that connect the cerebral cortex with other parts of the brainstem and spinal cord (Fig. 7-1). Since the diencephalon is divided into symmetrical halves by the slitlike third ventricle, it also has a medial surface. The medial surface of the diencephalon (i.e., the lateral wall of the third ventricle) is formed in its superior part by the medial surface of the thalamus and in its inferior part by the hypothalamus (Fig. 7-3; see also Atlas Plate 8). These two areas are separated from one another by a shallow sulcus, the hypothalamic sulcus. A bundle of nerve fibers, which are afferent fibers to the habenular nucleus, forms a ridge along the superior margin of the medial surface of the diencephalon and is called the stria medullaris thalami (Fig. 7-1). The diencephalon can be divided into four major parts: (1) the thalamus, (2) the subthalamus, (3) the epithalamus, and (4) the hypothalamus. Thalamus The thalamus is a large ovoid mass of gray matter that forms the major part of the diencephalon. It is a region of great functional importance and serves as a cell station to all the main sensory systems (except the olfactory pathway). The activities of the thalamus are closely related to that of the cerebral cortec and damage to the thalamus causes great loss of cerebral function. The thalamus is situated on each side of the third ventricle (Fig. 7-3; see also Atlas Plate 5). The anterior end of the thalamus is narrow and rounded and forms the posterior boundary of the interventricular foramen. The posterior end (Fig. 7-4) is expanded to form the pulvinar, which overhangs the superior colliculus and the superior brachium. The lateral geniculate body forms a small elevation on the under aspect of the lateral portion of the pulvinar. P.253

Figure 7-1 Horizontal section of the brain showing the third and lateral ventricles exposed by dissection from above.

The superior surface of the thalamus is covered medially by the tela choroidea and the fornix, and laterally, it is covered by ependyma and forms part of the floor of the lateral ventricle; the lateral part is partially hidden by the choroid plexus of the lateral ventricle (Fig. 7-1). The inferior surface is continuous with the tegmentum of the midbrain (Fig. 7-3). The medial surface of the thalamus forms the superior part of the lateral wall of the third ventricle and is usually connected to the opposite thalamus by a band of gray matter, the interthalamic connection (interthalamic adhesion) (Fig. 7-3). The lateral surface of the thalamus is separated from the lentiform nucleus by the very important band of white matter called the internal capsule (Fig. 7-1). The subdivisions of the thalamus (Fig. 7-4) and the detailed description of the thalamic nuclei and their connections are given on page 372. The thalamus is a very important cell station that receives the main sensory tracts (except the olfactory pathway). It should be regarded as a station where much of the information is integrated and relayed to the cerebral cortex and many other subcortical regions. It also plays a key role in the integration of visceral and somatic functions. For more information on the function of the thalamus, see page 375. Subthalamus The subthalamus lies inferior to the thalamus and, therefore, is situated between the thalamus and the tegmentum of the midbrain; craniomedially, it is related to the hypothalamus. The structure of the subthalamus is extremely complex, and only a brief description is given here. Among the collections of nerve cells found in the subthalamus are the cranial ends of the red nuclei and the substantia nigra. The subthalamic nucleus has the shape of a biconvex lens. The nucleus has important connections with the corpus striatum (see p. 263); as a result, it is involved in the control of muscle activity. P.254

Figure 7-2 Inferior surface of the brain showing parts of the diencephalon.
Figure 7-3 Sagittal section of the brain showing the medial surface of the diencephalon.

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Figure 7-4 Nuclei of the thalamus. A: Transverse section through the anterior end of the thalamus. B: Diagram showing the position of the thalamus within the right cerebral hemisphere and the relative position of the thalamic nuclei to one another.

The subthalamus also contains many important tracts that pass up from the tegmentum to the thalamic nuclei; the cranial ends of the medial, spinal, and trigeminal lemnisci are examples. Epithalamus The epithalamus consists of the habenular nuclei and their connections and the pineal gland. Habenular Nucleus The habenular nucleus is a small group of neurons situated just medial to the posterior surface of the thalamus. Afferent fibers are received from the amygdaloid nucleus in the temporal lobe (see p. 310) through the stria medullaris thalami; other fibers pass from the hippocampal formation through the fornix. Some of the fibers of the stria medullaris thalami cross the midline and reach the habenular nucleus of the opposite side; these latter fibers form the habenular commissure P.256 (Fig. 7-3). Axons from the habenular nucleus pass to the interpeduncular nucleus in the roof of the interpeduncular fossa, the tectum of the midbrain, the thalamus, and the reticular formation of the midbrain. The habenular nucleus is believed to be a center for integration of olfactory, visceral, and somatic afferent pathways. Pineal Gland (Body) The pineal gland is a small, conical structure that is attached by the pineal stalk to the diencephalon. It projects backward so that it lies posterior to the midbrain (Fig. 7-3; see also Atlas Plate 8). The base of the pineal stalk possesses a recess that is continuous with the cavity of the third ventricle (Fig. 7-3). The superior part of the base of the stalk contains the habenular commissure; the inferior part of the base of the stalk contains the posterior commissure. On microscopic section, the pineal gland is seen to be incompletely divided into lobules by connective tissue septa that extend into the substance of the gland from the capsule. Two types of cells are found in the gland, the pinealocytes and the glial cells. Concretions of calcified material called brain sand progressively accumulate within the pineal gland with age (Fig. 7-5). The pineal gland possesses no nerve cells, but adrenergic sympathetic fibers derived from the superior cervical sympathetic ganglia enter the gland and run in association with the blood vessels and the pinealocytes. Functions of the Pineal Gland The pineal gland, once thought to be of little significance, is now recognized as an important endocrine gland capable of influencing the activities of the pituitary gland, the islets of Langerhans of the pancreas, the parathyroids, the adrenal cortex and the adrenal medulla, and the gonads. The pineal secretions, produced by the pinealocytes, reach their target organs via the bloodstream or through the cerebrospinal fluid. Their actions are mainly inhibitory and either directly inhibit the production of hormones or indirectly inhibit the secretion of releasing factors by the hypothalamus. It is interesting to note that the pineal gland does not possess a blood-brain barrier.

Figure 7-5 Photomicrograph of a section of the pineal gland stained with hematoxylin and eosin.

Animal experiments have shown that pineal activity exhibits a circadian rhythm that is influenced by light. The gland has been found to be most active during darkness. The probable nervous pathway from the retina runs to the suprachiasmatic nucleus of the hypothalamus, then to the tegmentum of the midbrain, and then to the pineal gland to stimulate its secretions. The latter part of this pathway may include the reticulospinal tract, the sympathetic outflow of the thoracic part of the spinal cord, and the superior cervical sympathetic ganglion and postganglionic nerve fibers that travel to the pineal gland on blood vessels. Melatonin and the enzymes needed for its production are present in high concentrations within the pineal gland. Melatonin and other substances are released into the blood or into the cerebrospinal fluid of the third ventricle where they pass to the anterior lobe of the pituitary gland and inhibit the release of the gonadotrophic hormone. In humans, as in animals, the plasma melatonin level rises in darkness and falls during the day. It would appear that the pineal gland plays an important role in the regulation of reproductive function. Hypothalamus The hypothalamus is that part of the diencephalon that extends from the region of the optic chiasma to the caudal border of the mammillary bodies (Fig. 7-2; see also Atlas Plate 8). It lies below the hypothalamic sulcus on the lateral wall of the third ventricle. It is thus seen that anatomically the hypothalamus is a relatively small area of the brain that is strategically well placed close to the limbic system, the thalamus, the ascending and descending tracts, and the hypophysis. Microscopically, the hypothalamus is composed of small nerve cells that are arranged in groups or nuclei. The arrangement of these nuclei and their connections are fully described in Chapter 13. P.257 Physiologically, there is hardly any activity in the body that is not influenced by the hypothalamus. The hypothalamus controls and integrates the functions of the autonomic nervous system and the endocrine systems and plays a vital role in maintaining body homeostasis. It is involved in such activities as regulation of body temperature, body fluids, drives to eat and drink, sexual behavior, and emotion. Relations of the Hypothalamus Anterior to the hypothalamus is an area that extends forward from the optic chiasma to the lamina terminalis and the anterior commissure; it is referred to as the preoptic area. Caudally, the hypothalamus merges into the tegmentum of the midbrain. The thalamus lies superior to the hypothalamus, and the subthalamic region lies inferolaterally to the hypothalamus. When observed from below, the hypothalamus is seen to be related to the following structures, from anterior to posterior: (1) the optic chiasma, (2) the tuber cinereum and the infundibulum, and (3) the mammillary bodies. Optic Chiasma The optic chiasma is a flattened bundle of nerve fibers situated at the junction of the anterior wall and floor of the third ventricle (Figs. 7-2 and 7-3; see also Atlas Plate 8). The superior surface is attached to the lamina terminalis, and inferiorly, it is related to the hypophysis cerebri, from which it is separated by the diaphragma sellae. The anterolateral corners of the chiasma are continuous with the optic nerves, and the posterolateral corners are continuous with the optic tracts. A small recess, the optic recess of the third ventricle, lies on its superior surface. It is important to remember that the fibers originating from the nasal half of each retina cross the median plane at the chiasma to enter the optic tract of the opposite side. Tuber Cinereum The tuber cinereum is a convex mass of gray matter, as seen from the inferior surface (Figs. 7-2 and 7-3; see also Atlas Plate 8). It is continuous inferiorly with the infundibulum. The infundibulum is hollow and becomes continuous with the posterior lobe of the hypophysis cerebri. The median eminence is a raised part of the tuber cinereum to which is attached the infundibulum. The median eminence, the infundibulum, and the posterior lobe (pars nervosa) of the hypophysis cerebri together form the neurohypophysis. Mammillary Bodies The mammillary bodies are two small hemispherical bodies situated side by side posterior to the tuber cinereum (Figs. 7-2 and 7-3; see also Atlas Plate 8). They possess a central core of gray matter invested by a capsule of myelinated nerve fibers. Posterior to the mammillary bodies lies an area of the brain that is pierced by a number of small apertures and is called the posterior perforated substance. These apertures transmit the central branches of the posterior cerebral arteries. Third Ventricle The third ventricle, which is derived from the forebrain vesicle, is a slitlike cleft between the two thalami (Figs. 7-1 and 7-3; see also Atlas Plates 5 and 8). It communicates anteriorly with the lateral ventricles through the interventricular foramina (foramina of Monro), and it communicates posteriorly with the fourth ventricle through the cerebral aqueduct. The third ventricle has anterior, posterior, lateral, superior, and inferior walls and is lined with ependyma. The anterior wall is formed by a thin sheet of gray matter, the lamina terminalis, across which runs the anterior commissure (Fig. 7-3). The anterior commissure is a round bundle of nerve fibers that are situated anterior to the anterior columns of the fornix; they connect the right and left temporal lobes. The posterior wall is formed by the opening into the cerebral aqueduct (Fig. 7-3). Superior to this opening is the small posterior commissure. Superior to the commissure is the pineal recess, which projects into the stalk of the pineal body. Superior to the pineal recess is the small habenular commissure. The lateral wall is formed by the medial surface of the thalamus superiorly and the hypothalamus inferiorly (Fig. 7-3). These two structures are separated by the hypothalamic sulcus. The lateral wall is limited superiorly by the stria medullaris thalami. The lateral walls are joined by the interthalamic connection. The superior wall or roof is formed by a layer of ependyma that is continuous with the lining of the ventricle. Superior to this layer is a two-layered fold of pia mater called the tela choroidea of the third ventricle. The vascular tela choroidea projects downward on each side of the midline, invaginating the ependymal roof to form the choroid plexuses of the third ventricle. Within the tela choroidea lie the internal cerebral veins. Superiorly, the roof of the ventricle is related to the fornix and the corpus callosum. The inferior wall or floor is formed by the optic chiasma, the tuber cinereum, the infundibulum, with its funnel-shaped recess, and the mammillary bodies (Figs. 7-2 and 7-3). The hypophysis is attached to the infundibulum. Posterior to these structures lies the tegmentum of the cerebral peduncles. The ventricular system is fully described in Chapter 16. General Appearance of the Cerebral Hemispheres The cerebral hemispheres are the largest part of the brain; they are separated by a deep midline sagittal fissure, the longitudinal cerebral fissure (Fig. 7-6; see also Atlas Plates 1 and 2). The fissure contains the sickle-shaped fold of dura mater, the falx cerebri, and the anterior cerebral arteries. In the depths of the fissure, the great commissure, the corpus callosum, connects the hemispheres across the midline (Fig. 7-6). A second horizontal fold of dura mater separates the cerebral hemispheres from the cerebellum and is called the tentorium cerebelli. P.258

Figure 7-6 Superior view of the cerebral hemispheres.

To increase the surface area of the cerebral cortex maximally, the surface of each cerebral hemisphere is thrown into folds or gyri, which are separated from each other by sulci or fissures (Fig. 7-6). For ease of description, it is customary to divide each hemisphere into lobes, which are named according to the cranial bones under which they lie. The central and parieto-occipital sulci and the lateral and calcarine sulci are boundaries used for the division of the cerebral hemisphere into frontal, parietal, temporal, and occipital lobes (Figs. 7-7 and 7-11). Main Sulci The central sulcus (Fig. 7-7; see also Altas Plate 3) is of great importance because the gyrus that lies anterior to it contains the motor cells that initiate the movements of the opposite side of the body; posterior to it lies the general sensory cortex that receives sensory information from the opposite side of the body. The central sulcus indents the superior medial border of the hemisphere about 0.4 inch (1 cm) behind the midpoint (Fig. 7-8). It runs downward and forward across the lateral aspect of the hemisphere, and its lower end is separated from the posterior ramus of the lateral sulcus by a narrow bridge of cortex. The central sulcus is the only sulcus of any length on this surface of the hemisphere that indents the superomedial border and lies between two parallel gyri. The lateral sulcus (Fig. 7-7; see also Atlas Plate 3) is a deep cleft found mainly on the inferior and lateral surfaces of the cerebral hemisphere. It consists of a short stem that divides into three rami. The stem arises on the inferior surface, and on reaching the lateral surface, it divides into the anterior horizontal ramus and the anterior ascending ramus and continues as the posterior ramus (Figs. 7-7 and 7-10). An area of cortex called the insula lies at the bottom P.259 P.260 of the deep lateral sulcus and cannot be seen from the surface unless the lips of the sulcus are separated (Fig. 7-9).

Figure 7-7 Lateral view of the right cerebral hemisphere.
Figure 7-8 Medial view of the right cerebral hemisphere.
Figure 7-9 Lateral view of the right cerebral hemisphere dissected to reveal the right insula.

The parieto-occipital sulcus begins on the superior medial margin of the hemisphere about 2 inches (5 cm) anterior to the occipital pole (Figs. 7-8 and 7-10; see also Atlas Plate 3). It passes downward and anteriorly on the medial surface to meet the calcarine sulcus (Fig. 7-8). The calcarine sulcus is found on the medial surface of the hemisphere (Figs. 7-8 and 7-10; see also Atlas Plate 3). It commences under the posterior end of the corpus callosum and arches upward and backward to reach the occipital pole, where it stops. In some brains, however, it continues for a short distance onto the lateral surface of the hemisphere. The calcarine sulcus is joined at an acute angle by the parieto-occipital sulcus about halfway along its length. Lobes of the Cerebral Hemisphere Superolateral Surface of the Hemisphere (Atlas Plate 3) The frontal lobe occupies the area anterior to the central sulcus and superior to the lateral sulcus (Figs. 7-10 and 7-11). The superolateral surface of the frontal lobe is divided by three sulci into four gyri. The precentral sulcus runs parallel to the central sulcus, and the precentral gyrus lies between them (Figs. 7-7 and 7-10). Extending anteriorly from the precentral sulcus are the superior and inferior frontal sulci. The superior frontal gyrus lies superior to the superior frontal sulcus, the middle frontal gyrus lies between the superior and inferior frontal sulci, and the inferior frontal gyrus lies inferior to the inferior frontal sulcus (Figs. 7-7 and 7-10). The inferior frontal gyrus is invaded by the anterior and ascending rami of the lateral sulcus. The parietal lobe occupies the area posterior to the central sulcus and superior to the lateral sulcus; it extends posteriorly as far as the parieto-occipital sulcus (Figs. 7-7, 7-8, 7-9, 7-10 and 7-11). The lateral surface of the parietal lobe is divided by two sulci into three gyri. The postcentral sulcus runs parallel to the central sulcus, and the postcentral gyrus lies between them. Running posteriorly from the middle of the postcentral sulcus is the intraparietal sulcus (Figs. 7-7 and 7-10). Superior to the intraparietal sulcus is the superior parietal lobule (gyrus), and inferior to the intraparietal sulcus is the inferior parietal lobule (gyrus). The temporal lobe occupies the area inferior to the lateral sulcus (Figs. 7-7, 7-8, 7-9, 7-10 and 7-11). The lateral surface of the temporal lobe is divided into three gyri by two sulci. The superior and middle temporal sulci run parallel to the posterior ramus of the lateral sulcus and divide the temporal lobe into the superior, middle, and inferior temporal gyri; the inferior temporal gyrus is continued onto the inferior surface of the hemisphere (Figs. 7-7 and 7-10). P.261

Figure 7-10 A: Lateral view of the right cerebral hemisphere showing the main sulci. B: Medial view of the right cerebral hemisphere showing the main sulci.

The occipital lobe occupies the small area behind the parieto-occipital sulcus (Figs. 7-7, 7-8, 7-9, 7-10 and 7-11). Medial and Inferior Surfaces of the Hemisphere (Atlas Plates 3, 6, and 8) The lobes of the cerebral hemisphere are not clearly defined on the medial and inferior surfaces. However, there are many important areas that should be recognized. The corpus callosum, which is the largest commissure of the brain, forms a striking feature on this surface (Figs. 7-8 and 7-10). The cingulate gyrus begins beneath the anterior end of the corpus callosum and continues above the corpus callosum until it reaches its posterior end (Figs. 7-8 and 7-10). The gyrus is separated from the corpus callosum by the callosal sulcus. The cingulate gyrus is separated from the superior frontal gyrus by the cingulate sulcus (Fig. 7-10). The paracentral lobule is the area of the cerebral cortex that surrounds the indentation produced by the central sulcus on the superior border (Figs. 7-8 and 7-10). The anterior part of this lobule is a continuation of the precentral gyrus on the superior lateral surface, and the posterior part of the lobule is a continuation of the postcentral gyrus. P.262

Figure 7-11 A: Lateral view of the right cerebral hemisphere showing the lobes. B: Medial view of the right cerebral hemisphere showing the lobes. Note that the dashed lines indicate the approximate position of the boundaries where there are no sulci.

The precuneus (Figs. 7-8 and 7-10) is an area of cortex bounded anteriorly by the upturned posterior end of the cingulate sulcus and posteriorly by the parieto-occipital sulcus. The cuneus (Figs. 7-8 and 7-10) is a triangular area of cortex bounded above by the parieto-occipital sulcus, inferiorly by the calcarine sulcus, and posteriorly by the superior medial margin. The collateral sulcus is situated on the inferior surface of the hemisphere (Figs. 7-8 and 7-12). This runs anteriorly below the calcarine sulcus. Between the collateral sulcus and the calcarine sulcus is the lingual gyrus. Anterior to the lingual gyrus is the parahippocampal gyrus; the latter terminates in front as the hooklike uncus (Fig. 7-12). The medial occipitotemporal gyrus extends from the occipital pole to the temporal pole (Fig. 7-12). It is bounded medially by the collateral and rhinal sulci and laterally by the occipitotemporal sulcus. The occipitotemporal gyrus lies lateral to the sulcus and is continuous with the inferior temporal gyrus (Fig. 7-12). On the inferior surface of the frontal lobe, the olfactory bulb and tract overlie a sulcus called the olfactory sulcus (Fig. 7-12). Medial to the olfactory sulcus is the gyrus rectus, and lateral to the sulcus are a number of orbital gyri. Internal Structure of the Cerebral Hemispheres (Atlas Plates 4 and 5) The cerebral hemispheres are covered with a layer of gray matter, the cerebral cortex; the structure and function of the cerebral cortex are discussed in Chapter 15. Located in the interior of the cerebral hemispheres are the lateral ventricles, masses of gray matter, the basal nuclei, and nerve fibers. The nerve fibers are embedded in neuroglia and constitute the white matter (Fig. 7-13). P.263

Figure 7-12 Inferior view of the brain; the medulla oblongata, the pons, and the cerebellum have been removed.

Lateral Ventricles There are two lateral ventricles, and one is present in each cerebral hemisphere (Figs. 7-13 and 7-14). Each ventricle is a roughly C-shaped cavity lined with ependyma and filled with cerebrospinal fluid. The lateral ventricle may be divided into a body, which occupies the parietal lobe, and from which anterior, posterior, and inferior horns extend into the frontal, occipital, and temporal lobes, respectively. The lateral ventricle communicates with the cavity of the third ventricle through the interventricular foramen (Figs. 7-8 and 7-14). This opening, which lies in the anterior part of the medial wall of the lateral ventricle, is bounded anteriorly by the anterior column of the fornix and posteriorly by the anterior end of the thalamus. Basal Nuclei The term basal nuclei (basal ganglia) is applied to a collection of masses of gray matter situated within each cerebral hemisphere. They are the corpus striatum, the amygdaloid nucleus, and the claustrum. Corpus Striatum The corpus striatum is situated lateral to the thalamus. It is almost completely divided by a band of nerve fibers, the internal capsule, into the caudate nucleus and the lentiform nucleus (Figs. 7-13 and 7-18). The caudate nucleus, a large C-shaped mass of gray matter that is closely related to the lateral ventricle, lies P.264 lateral to the thalamus (Fig. 7-15). The lateral surface of the nucleus is related to the internal capsule, which separates it from the lentiform nucleus.

Figure 7-13 Horizontal section of the cerebrum, as seen from above, showing the relationship between the lentiform nucleus, the caudate nucleus, the thalamus, and the internal capsule.

The lentiform nucleus is a wedge-shaped mass of gray matter whose broad convex base is directed laterally and its blade medially (Figs. 7-13 and 7-15). It is buried deep in the white matter of the cerebral hemisphere and is related medially to the internal capsule, which separates it from the caudate nucleus and the thalamus. The lentiform nucleus is related laterally to a thin sheet of white matter, the external capsule (Fig. 7-13), that separates it from a thin sheet of gray matter, called the claustrum (Fig. 7-13). The claustrum, in turn, separates the external capsule from the subcortical white matter of the insula. Inferiorly at its anterior end, the lentiform nucleus is continuous with the caudate nucleus. The detailed structure and connections of the corpus striatum are considered in Chapter 10. Briefly, it may be stated that the corpus striatum receives afferent fibers from different areas of the cerebral cortex, the thalamus, subthalamus, and brainstem. Efferent fibers then travel back to the same areas of the nervous system. The function of the corpus striatum is concerned with muscular movement, which is accomplished by controlling the cerebral cortex rather than through direct descending pathways to the brainstem and spinal cord. Amygdaloid Nucleus The amygdaloid nucleus is situated in the temporal lobe close to the uncus (Fig. 7-15). The amygdaloid nucleus is considered part of the limbic system and is described in Chapter 9 (see p. 310). Claustrum The claustrum is a thin sheet of gray matter that is separated from the lateral surface of the lentiform nucleus by the external capsule (Fig. 7-13). Lateral to the claustrum is the subcortical white matter of the insula. The function of the claustrum is unknown. P.265

Figure 7-14 Ventricular cavities of the brain. A: Lateral view. B: Superior view.

White Matter of the Cerebral Hemispheres The white matter is composed of myelinated nerve fibers of different diameters supported by neuroglia. The nerve fibers may be classified into three groups according to their connections: (1) commissural fibers, (2) association fibers, and (3) projection fibers. Commissure Fibers Commissure fibers essentially connect corresponding regions of the two hemispheres. They are as follows: the corpus callosum, the anterior commissure, the posterior commissure, the fornix, and the habenular commissure. The corpus callosum, the largest commissure of the brain, connects the two cerebral hemispheres (Figs. 7-8 and 7-16; see also Atlas Plate 8). It lies at the bottom of the longitudinal fissure. For purposes of description, it is divided into the rostrum, the genu, the body, and the splenium. The rostrum is the thin part of the anterior end of the corpus callosum, which is prolonged posteriorly to be continuous with the upper end of the lamina terminalis (Fig. 7-8). The genu is the curved anterior end of the corpus callosum that bends inferiorly in front of the septum pellucidum (Figs. 7-8 and 7-16). The body of the corpus callosum arches posteriorly and ends as the thickened posterior portion called the splenium (Fig. 7-16). Traced laterally, the fibers of the genu curve forward into the frontal lobes and form the forceps minor (Fig. 7-16). The fibers of the body extend laterally as the radiation of the corpus callosum (Fig. 7-16). They intersect with bundles of association and projection fibers as they pass to the cerebral cortex. Some of the fibers form the roof and lateral wall of the posterior horn of the lateral ventricle and the lateral wall of the inferior horn of the lateral ventricle; these fibers are referred to as the tapetum. Traced laterally, the fibers in the splenium arch backward into the occipital lobe and form the forceps major (Fig. 7-16). The anterior commissure is a small bundle of nerve fibers that crosses the midline in the lamina terminalis (Fig. 7-8). When traced laterally, a smaller or anterior bundle curves forward on each side toward the anterior perforated substance and the olfactory tract. A larger bundle curves posteriorly on each side and grooves the inferior surface of the lentiform nucleus to reach the temporal lobes. The posterior commissure is a bundle of nerve fibers that crosses the midline immediately above the opening of the cerebral aqueduct into the third ventricle (Fig. 7-3); it is P.266 related to the inferior part of the stalk of the pineal gland. Various collections of nerve cells are situated along its length. The destinations and functional significance of many of the nerve fibers are not known. However, the fibers from the pretectal nuclei involved in the pupillary light reflex are believed to cross in this commissure on their way to the parasympathetic part of the oculomotor nuclei.

Figure 7-15 Lateral view of the right cerebral hemisphere dissected to show the position of the lentiform nucleus, the caudate nucleus, the thalamus, and the hippocampus.

The fornix is composed of myelinated nerve fibers and constitutes the efferent system of the hippocampus that passes to the mammillary bodies of the hypothalamus. The nerve fibers first form the alveus (see Fig. 9-5), which is a thin layer of white matter covering the ventricular surface of the hippocampus, and then converge to form the fimbria. The fimbriae of the two sides increase in thickness and, on reaching the posterior end of the hippocampus, arch forward above the thalamus and below the corpus callosum to form the posterior columns of the fornix. The two columns then come together in the midline to form the body of the fornix (Fig. 7-17). A more detailed description of the fornix is given on page 310. The commissure of the fornix consists of transverse fibers that cross the midline from one column to another just before the formation of the body of the fornix. The function of the commissure of the fornix is to connect the hippocampal formations of the two sides. The habenular commissure is a small bundle of nerve fibers that crosses the midline in the superior part of the root of the pineal stalk (Fig. 7-3). The commissure is associated with the habenular nuclei, which are situated on either side of the midline in this region. The habenular nuclei receive many afferents from the amygdaloid nuclei and the hippocampus. These afferent fibers pass to the habenular nuclei in the stria medullaris thalami. Some of the fibers cross the midline to reach the contralateral nucleus through the habenular commissure. The function of the habenular nuclei and its connections in humans is unknown. Association Fibers Association fibers are nerve fibers that essentially connect various cortical regions within the same hemisphere and may be divided into short and long groups (Fig. 7-19). The short association fibers lie immediately beneath the cortex and connect adjacent gyri; these fibers run transversely to the long axis of the sulci (Fig. 7-19). The long association fibers are collected into named bundles that can be dissected in a formalin-hardened brain. The uncinate fasciculus connects the first motor speech area and the gyri on the inferior surface of the frontal lobe with the cortex of the pole of the temporal lobe. The cingulum is a long, curved fasciculus lying within the white matter of the cingulate gyrus (Fig. 7-8). It connects the frontal and parietal lobes with parahippocampal and adjacent temporal cortical regions. The superior longitudinal fasciculus is the largest bundle of nerve fibers. It connects the anterior part of the frontal lobe to the occipital and temporal lobes. The inferior longitudinal fasciculus runs anteriorly from the occipital lobe, passing lateral to the optic radiation, P.267 P.268 and is distributed to the temporal lobe. The fronto-occipital fasciculus connects the frontal lobe to the occipital and temporal lobes. It is situated deep within the cerebral hemisphere and is related to the lateral border of the caudate nucleus.

Figure 7-16 A: Coronal section of the brain passing through the anterior horn of the lateral ventricle and the optic chiasma. B: Superior view of the brain dissected to show the fibers of the corpus callosum and the corona radiata.
Figure 7-17 Horizontal section of the brain leaving the fornix in position.

Projection Fibers Afferent and efferent nerve fibers passing to and from the brainstem to the entire cerebral cortex must travel between large nuclear masses of gray matter within the cerebral hemisphere. At the upper part of the brainstem, these fibers form a compact band known as the internal capsule, which is flanked medially by the caudate nucleus and the thalamus and laterally by the lentiform nucleus (Fig. 7-13). Because of the wedge shape of the lentiform nucleus, as seen on horizontal section, the internal capsule is bent to form an anterior limb and a posterior limb, which are continuous with each other at the genu (Figs. 7-18 and 7-20). Once the nerve fibers have emerged superiorly from between the nuclear masses, they radiate in all directions to the cerebral cortex. These radiating projection fibers are known as the corona radiata (Fig. 7-20). Most of the projection fibers lie medial to the association fibers, but they intersect the commissural fibers of the corpus callosum and the anterior commissure. The nerve fibers lying within the most posterior part of the posterior limb of the internal capsule radiate toward the calcarine sulcus and are known as the optic radiation (Fig. 7-18). The detailed arrangement of the fibers within the internal capsule is shown in Figure 7-18. Septum Pellucidum The septum pellucidum is a thin vertical sheet of nervous tissue consisting of white and gray matter covered on either side by ependyma (Figs. 7-8 and 7-13; see also Atlas Plate 8). It stretches between the fornix and the corpus callosum. Anteriorly, it occupies the interval between the body of the corpus callosum and the rostrum. It is essentially a double membrane with a closed, slitlike cavity between the membranes. The septum pellucidum forms a partition between the anterior horns of the lateral ventricles. Tela Choroidea The tela choroidea is a two-layered fold of pia mater. It is situated between the fornix superiorly and the roof of the third ventricle and the upper surfaces of the two thalami inferiorly. When seen from above, the anterior end is situated at the interventricular foramina (see Fig. 16-6). Its lateral edges are irregular and project laterally into the body of the lateral ventricles. Here, they are covered by ependyma and form the choroid plexuses of the lateral ventricle. Posteriorly, the lateral edges continue into the inferior horn of the lateral ventricle and are covered with ependyma so that the choroid plexus projects through the choroidal fissure. On either side of the midline, the tela choroidea projects down through the roof of the third ventricle to form the choroid plexuses of the third ventricle. The blood supply of the tela choroidea and, therefore, also of the choroid plexuses of the third and lateral ventricles is derived from the choroidal branches of the internal carotid and basilar arteries. The venous blood drains into the internal cerebral veins, which unite to form the great cerebral vein. The great cerebral vein joins the inferior sagittal sinus to form the straight sinus. P.269

Figure 7-18 Horizontal section of the right cerebral hemisphere showing the relationships and different parts of the internal capsule.

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Figure 7-19 Lateral view of the right cerebral hemisphere, which has been dissected to show some of the principal association fibers.
Figure 7-20 Medial view of the right cerebral hemisphere, which has been dissected to show the internal capsule and the corona radiata. The thalamus has been removed. Note the interdigitation of the horizontally running fibers of the corpus callosum and the vertical fibers of the corona radiata.

P.271 P.272 P.273 P.274 P.275 P.276 Clinical Notes Lesions of the Thalamus Lesions of the thalamus usually result from thrombosis or hemorrhage of one of the arteries that supply the thalamus. Since the thalamus is concerned with receiving sensory impulses from the opposite side of the body, the disability resulting from a lesion within it will be confined to the contralateral side of the body. There may be a major impairment of all forms of sensation, which could include light touch, tactile localization and discrimination, and loss of appreciation of joint movements. Subthalamic Lesions The subthalamus should be regarded as one of the extrapyramidal motor nuclei and has a large connection with the globus pallidus. Lesions of the subthalamus result in sudden, forceful involuntary movements in a contralateral extremity. The movements may be jerky (choreiform) or violent (ballistic). Pineal Gland The pineal gland consists essentially of pinealocytes and glial cells supported by a connective tissue framework. As the result of regressive changes that occur with age, calcareous concretions accumulate within the glial cells and connective tissue of the gland. These deposits are useful to the radiologist, since they serve as a landmark and assist in determining whether the pineal gland has been displaced laterally by a space-occupying lesion within the skull. The functions of the pineal gland are mainly inhibitory and have been shown to influence the pituitary gland, the islets of Langerhans, the parathyroids, the adrenals, and the gonads. Clinical observation of patients with pineal tumors or tumors of neighboring areas of nervous tissue that may press on the pineal gland has shown severe alteration of reproductive function. Hypothalamus The hypothalamus is an area of the nervous system that is of great functional importance. Not only does it control emotional states, but it also assists in the regulation of fat, carbohydrate, and water metabolism. Among its many other activities, it influences body temperature, genital functions, sleep, and food intake. The pituitary and the hypothalamus constitute a closely integrated unit, and the hypothalamus plays a role in the release of pituitary hormones. Syndromes of the Hypothalamus Lesions of the hypothalamus may result from infection, trauma, or vascular disorders. Tumors, such as a craniopharyngioma or chromophobe adenoma of the pituitary and pineal tumors, may interfere with the function of the hypothalamus. The most common abnormalities include genital hypoplasia or atrophy, diabetes insipidus, obesity, disturbances of sleep, irregular pyrexia, and emaciation. Some of these disorders may occur together, such as in the adiposogenital dystrophy syndrome. Cerebral Cortex, Sulci, and Lobes of the Cerebral Hemisphere The cerebral cortex is composed of gray matter. Only about one-third lies on the exposed convexity of the gyri; the remaining two-thirds form the walls of the sulci. Moreover, different areas of the cortex have different functions, and the anatomical division of the cortex into lobes and gyri by sulci enables the physician to localize loss of function or accurately place a brain lesion. For example, focal lesions of the precentral gyrus will produce contralateral hemiparesis, while lesions of the postcentral gyrus will result in contralateral hemisensory loss. More widespread lesions of the frontal lobe might cause symptoms and signs indicative of loss of attention span or change in social behavior. Widespread degeneration of the cerebral cortex gives rise to symptoms of dementia. Lateral Ventricles Each lateral ventricle contains about 7 to 10 mL of cerebrospinal fluid. This fluid is produced in the choroid plexus of the lateral ventricle and normally drains into the third ventricle through the interventricular foramen (foramen of Monro). Blockage of the foramen by a cerebral tumor would result in distention of the ventricle, thus producing a type of hydrocephalus. The choroid plexus of the lateral ventricle is continuous with that of the third ventricle through the interventricular foramen. The choroid plexus is largest where the body and posterior and inferior horns join, and it is here where it may become calcified with age. It is important that this calcification of the choroid plexus, as seen on radiographs, is not confused with that of the pineal gland. In the past, the size and shape of the lateral ventricle were investigated clinically by pneumoencephalography (Figs. 7-21, 7-22, 7-23 and 7-24). In this procedure, small amounts of air were introduced into the subarachnoid space by lumbar puncture with the patient in the sitting position. If the patient already had a raised intracranial pressure, this method was dangerous (see p. 24), and air or radiopaque fluid was injected directly into the lateral ventricles through a burr hole in the skull (this procedure was referred to as ventriculography). This procedure has now been replaced by CT and magnetic resonance imaging (MRI) (Figs. 7-25, 7-26, 7-27 and 7-28).

Figure 7-21 Anteroposterior pneumoencephalogram of a 28-year-old man.
Figure 7-22 Explanation of the radiograph seen in Figure 7-21. Note the position of the x-ray gun relative to the head and the film cassette.
Figure 7-23 Lateral pneumoencephalogram of a 28-year-old man.

Basal Nuclei The basal nuclei, in this discussion, refers to the masses of gray matter that are deeply placed within the cerebrum. They include the caudate nucleus, the lentiform nucleus, the amygdaloid nucleus, and the claustrum. Because of the close relationship that exists between these nuclei and the internal capsule, tumors of the caudate or lentiform nuclei may cause severe motor or sensory symptoms on the opposite side of the body. Tumors pressing on the anterior two-thirds of the posterior limb of the internal capsule will cause progressive spastic hemiplegia, while more posteriorly situated tumors will produce impairment of sensation on the opposite side. Disorders of function of the basal nuclei are considered after the connections of these nuclei are discussed in Chapter 10. Commissures of the Cerebrum The major commissure is the large corpus callosum. The majority of the fibers within the corpus callosum interconnect symmetrical areas of the cerebral cortex. Because it transfers information from one hemisphere to another, the corpus callosum is essential for learned discrimination, sensory experience, and memory. Occasionally, the corpus callosum fails to develop, and in these individuals, no definite signs or symptoms appear. Should the corpus callosum be destroyed by disease in later life, however, each hemisphere becomes isolated, and the patient responds as if he or she has two separate brains. The patient’s general intelligence and behavior appear normal, since over the years both hemispheres have been trained to respond to different situations. If a pencil is placed in the patient’s right hand (with the eyes closed), he or she will recognize the object by touch and be able to describe it. If the pencil is placed in the left hand, the tactile information will pass to the right postcentral gyrus. This information will not be able to travel through the corpus callosum to the speech area in the left hemisphere; therefore, the patient will be unable to describe the object in his or her left hand. Section of the corpus callosum has been attempted surgically, with some success, in order to prevent the spread of seizures from one hemisphere to the other. Lesions of the Internal Capsule The internal capsule is an important compact band of white matter. It is composed of ascending and descending nerve fibers that connect the cerebral cortex to the brainstem and spinal cord. The internal capsule is flanked medially by the caudate nucleus and thalamus and laterally by the lentiform nucleus. The arrangement of the nerve fibers within the internal capsule is shown in Figure 7-18. The internal capsule is frequently involved in vascular disorders of the brain. The most common cause of arterial hemorrhage is atheromatous degeneration in an artery in a patient with high blood pressure. Because of the high concentration of important nerve fibers within the internal capsule, even a small hemorrhage can cause widespread effects on the contralateral side of the body. Not only is the immediate neural tissue destroyed by the blood, which later clots, but also neighboring nerve fibers may be compressed or be edematous. Alzheimer Disease Alzheimer disease is a degenerative disease of the brain occurring in middle to late life, but an early form of the disease is now well recognized. The disease affects more than 4 million people in the United States, resulting in over 100,000 deaths per year. The risk of the disease rises sharply with advancing years. The cause of Alzheimer disease is unknown, but there is evidence of a genetic predisposition. Several abnormal genes have been found, each of which leads to a similar clinical and pathologic syndrome, with only variations in the age of onset and the rate of progression to suggest that there are differences in the pathogenetic mechanisms. Some cases of familial Alzheimer disease, for example, have been shown to have mutations in several genes (App, presenilin 1, and presenilin 2). Early memory loss, a disintegration of personality, complete disorientation, deterioration in speech, and restlessness are common signs. In the late stages, the patient may become mute, incontinent, and bedridden and usually dies of some other disease. Microscopically, changes eventually occur throughout the cerebral cortex, but to begin with, certain regions of the brain are selectively involved. The early sites include the hippocampus, the entorhinal cortex, and the associated areas of the cerebral cortex. Many so-called senile plaques are found in the atrophic cortex. The plaques result from the accumulation of several proteins around deposits of beta amyloid. In the center of each plaque is an extracellular collection of degenerating nervous tissue; surrounding the core is a rim of large abnormal neuronal processes, probably presynaptic terminals, filled with an excess of intracellular neurofibrils that are tangled and twisted, forming neurofibrillary tangles. The neurofibrillary tangles are aggregations of the microtubular protein tau, which is hyperphosphorylated. There is a marked loss of choline acetyltransferase, the biosynthetic enzyme for acetylcholine, in the areas of the cortex in which the senile plaques occur. This is thought to be due to loss of the ascending projection fibers rather than a loss of cortical cells. As these cellular changes occur, the affected neurons die.

Figure 7-24 Explanation of the radiograph seen in Figure 7-23. Note the position of the x-ray gun relative to the head and the film cassette.
Figure 7-25 Horizontal (axial) CT scan of the brain.
Figure 7-26 Horizontal (axial) CT scan of the brain (contrast enhanced).
Figure 7-27 Horizontal (axial) MRI of the brain.
Figure 7-28 Coronal MRI of the brain.

At this time, there is no clinical test for making the definite diagnosis of Alzheimer disease. Reliance is placed on taking a careful history and carrying out numerous neurologic and psychiatric examinations spaced out over time. In this way, other causes of dementia can be excluded. Alterations in the levels of amyloid peptides or tau in the serum or cerebrospinal fluid may be helpful. CT scans or MRIs are also used, and abnormalities in the medial part of the temporal lobe occur in this disease. In advanced cases, a thin, atrophied cerebral cortex and dilated lateral ventricles may be found. The recent use of positron emission tomography (PET) shows evidence of diminished cortical metabolism (Fig. 7-29). The use of cholinesterase inhibitors for the treatment of Alzheimer disease has been found to be helpful. These drugs probably act by increasing the presence of acetylcholine at the sites of the disease where there is a deficiency of this neurotransmitter.

Figure 7-29 Axial (horizontal) PET scan of a male patient with Alzheimer disease, showing defects (arrowheads) in metabolism in the bitemporoparietal regions of the cerebral cortex, following the injection of 18-fluorodeoxyglucose. The yellow areas indicate regions of high metabolic activity. (Courtesy Dr. Holley Dey.)

P.277 P.278 Clinical Problem Solving 1. A 53-year-old woman was admitted to an emergency department after she had collapsed in the street. Apart from being confused and disoriented, she exhibited violent, uncoordinated movements of her right arm and right leg and slight spontaneous movements on the right side of her face. The physician was able to ascertain from a friend that the patient had been perfectly fit that morning and had no previous history of this condition. On examination, the involuntary movements of the right limbs were mainly confined to the muscles of the proximal part of the limbs. One week later, the patient died of cardiac failure. What is the medical term used to describe this condition? Which area of the brain is likely to be involved in the production of this condition? View Answer1. This woman exhibited continuous uncoordinated activity of the proximal musculature of the right arm and right leg, resulting in the limbs being flung violently about. The muscles of the right side of the face were also slightly affected. This condition is known as hemiballismus. It was caused by hemorrhage into the left subthalamic nucleus. 2. A 64-year-old man was admitted to a hospital on the suspicion that he had a cerebral tumor. One of the investigations asked for by the physician was a simple anteroposterior radiograph and lateral radiograph of the head. Using your knowledge of neuroanatomy, name the structure that would assist the radiologist in this case in determining whether lateral displacement of the brain had occurred within the skull. View Answer2. During the third decade of life, calcareous concretions appear in the neuroglia and connective tissue of the pineal gland. This provides a useful midline landmark to the radiologist. A lateral displacement of such a landmark would indicate the presence of an intracranial mass. In this patient, the pineal gland shadow was in the midline, and all the other investigations, including CT, showed no evidence of a cerebral tumor. 3. A 12-year-old boy was seen by a pediatrician because his parents were concerned about his excessive weight and lack of development of the external genitalia. On examination, the child was seen to be tall for his age and very obese. The excessive fat was concentrated especially in the lower part of the anterior abdominal wall and the proximal parts of the limbs. His penis and testes were small. Is it possible that disease of the diencephalon might account for this condition? View Answer3. Yes. Adiposity alone or associated with genital dystrophy can occur with disease of the hypothalamus. 4. A neurosurgeon explained to her residents that she would attempt to remove a glioma located in the right middle frontal gyrus by turning back a flap of the scalp and removing a rectangular piece of the overlying skull. Where exactly is the right middle frontal gyrus in the brain? What are the names of the sulci that lie above and below this gyrus? Which skull bone overlays this gyrus? View Answer4. The right middle frontal gyrus is located on the lateral surface of the frontal lobe of the right cerebral hemisphere. It is bounded superiorly and inferiorly by the superior and inferior frontal sulci, respectively. The right middle frontal gyrus is overlaid by the frontal bone of the skull. 5. While performing an autopsy, a pathologist had great difficulty in finding the central sulcus in each cerebral hemisphere. Since finding this sulcus is the key to localizing many other sulci and gyri, what landmarks would you use to identify the central sulcus? Are the sulci and gyri in the two hemispheres similar in size and shape? Are there individual variations in the arrangement of the sulci and gyri? View Answer5. The important central sulcus is large and runs downward and forward across the lateral aspect of each hemisphere. Superiorly, it indents the superior medial border of the hemisphere about 1 cm behind the midpoint; it lies between two parallel gyri. It is the only sulcus of any length that indents the superior medial border. The arrangement of the sulci and gyri is very similar on both sides of the brain. There are, however, great individual variations in the details of their arrangement. 6. A fourth-year medical student was shown coronal and horizontal MRIs of the brain and was asked to comment on his observations. The patient was a 55-year-old man. The student responded by saying that the left lateral ventricle was larger than normal and that there was an area of low signal intensity close to the left interventricular foramen suggesting the presence of a brain tumor. On looking at a standard lateral radiograph of the skull and brain, he noted a small area of “calcification” situated in the region of the posterior part of the left ventricle. Using your knowledge of neuroanatomy, describe the location of the lateral ventricle in the brain. What are the different parts of the lateral ventricle? Where is the cerebrospinal fluid in the lateral ventricle produced, and what does it normally drain into? What is responsible for the calcification seen in the left lateral ventricle in this patient? View Answer6. The lateral ventricle is a C-shaped cavity situated within each cerebral hemisphere. The lateral ventricle wraps itself around the thalamus, the lentiform nucleus, and the caudate nucleus. It is divided into a body that occupies the parietal lobe, an anterior horn that extends into the frontal lobe, a posterior horn that extends into the occipital lobe, and an inferior horn that runs forward and inferiorly into the temporal lobe. The cerebrospinal fluid is produced in the choroid plexus of the lateral ventricle and drains through the small interventricular foramen into the third ventricle. In later life, the choroid plexus, especially in its posterior part, sometimes shows calcified deposits, which are occasionally revealed on radiographs, as in this case. This patient later was found to have a cerebral tumor that was compressing the left interventricular foramen, hence the enlarged left ventricle. 7. A medical student, while performing an autopsy, found that the patient had no corpus callosum. On consulting the patient’s clinical notes, she was surprised to find no reference to a neurologic disorder. Are you surprised that this patient had no recorded neurologic signs and symptoms? View Answer7. No. The corpus callosum occasionally fails to develop, and in those patients, no definite neurologic signs and symptoms appear. If, however, the corpus callosum is divided during a surgical procedure in the adult, the loss of interconnections between the two hemispheres becomes apparent (see p. 273). P.279 P.280 P.281 P.282 Review Questions Directions: Each of the numbered items in this section is followed by answers. Select the ONE lettered answer that is CORRECT. 1. The following statements concern the diencephalon: (a) It extends anteriorly as far as the optic chiasma. (b) It is bounded laterally by the internal capsule. (c) The thalamus is located in the medial wall of the third ventricle. (d) The epithalamus is formed by the cranial end of the substantia nigra and the red nuclei. (e) It extends posteriorly as far as the interthalamic connection. View Answer1. B is correct. The diencephalon is bounded laterally by the internal capsule (see Fig. 7-1). A. The diencephalon extends anteriorly as far as the interventricular foramen (see Fig. 7-3). C. The thalamus is situated on the lateral wall of the third ventricle (see Fig. 7-3). D. The epithalamus consists of the habenular nuclei and their connections and the pineal gland (see p. 255). E. The diencephalon extends posteriorly as far as the cerebral aqueduct (see Fig. 7-3). 2. The following statements concern the pineal gland: (a) It produces a secretion that is opaque to x-rays. (b) It contains high concentrations of melatonin. (c) Melatonin stimulates the release of the gonadotrophic hormone from the anterior lobe of the pituitary gland. (d) There is a decrease in the production of secretions of the pineal gland during darkness. (e) The pinealocytes are inhibited by the sympathetic nerve endings. View Answer2. B is correct. The pineal gland contains high concentrations of melatonin (see p. 256). A. The pineal secretions are translucent to x-rays. C. Melatonin inhibits the release of the gonadotrophic hormone from the anterior lobe of the pituitary gland (see p. 256). D. There is an increased production of the secretions of the pineal gland during darkness. E. The pinealocytes are stimulated by the sympathetic nerve endings (see p. 256). 3. The following statements concern the thalamus: (a) It is the largest part of the diencephalon and serves as a relay station to all the main sensory tracts (except the olfactory pathway). (b) It is separated from the lentiform nucleus by the external capsule. (c) It forms the anterior boundary of the interventricular foramen. (d) It is completely separate from the thalamus on the opposite side. (e) The thalamus is a small rectangular mass of gray matter. View Answer3. A is correct. The thalamus is the largest part of the diencephalon and serves as a relay station to all the main sensory tracts, except the olfactory pathway (see p. 252). B. The thalamus is separated from the lentiform nucleus by the internal capsule (see Fig. 7-1). C. The thalamus forms the posterior boundary of the interventricular foramen (see Fig. 7-3). D. The thalamus may be joined to the thalamus of the opposite side by the interthalamic connection (see p. 253). E. The thalamus is a large ovoid mass of gray matter (see Fig. 7-4). 4. The following statements concern the hypothalamus: (a) It is formed by the upper part of the lateral wall and roof of the third ventricle. (b) Caudally, the hypothalamus merges with the tectum of the midbrain. (c) The nuclei are composed of groups of large nerve cells. (d) Functionally, it plays a role in the release of pituitary hormones. (e) The mammillary bodies are not part of the hypothalamus. View Answer4. D is correct. The hypothalamus plays an important role in the release of pituitary hormones (see p. 388). A. The hypothalamus is formed by the lower part of the lateral wall and floor of the third ventricle, below the hypothalamic sulcus (see Fig. 7-3). B. Caudally, the hypothalamus merges with the tegmentum of the midbrain (see p. 257). C. The nuclei of the hypothalamus are composed of groups of small nerve cells (see p. 256). E. The mammillary bodies are part of the hypothalamus (see p. 256). 5. The following statements concern the hypothalamus: (a) The hypothalamus has no influence on the activities of the autonomic and endocrine systems. (b) It receives few afferent visceral and somatic sensory fibers. (c) It gives off efferent fibers that pass to the sympathetic and parasympathetic outflows in the brain and spinal cord. (d) It does not assist in the regulation of water metabolism. (e) The hypothalamus plays no role in controlling emotional states. View Answer5. C is correct. The hypothalamus gives off efferent fibers that pass to the sympathetic and parasympathetic outflows in the brain and spinal cord (see p. 387). A. The hypothalamus has influence on the activities of the autonomic and endocrine systems (see p. 257). B. The hypothalamus receives many afferent visceral and somatic sensory nerve fibers (see p. 385). D. The hypothalamus assists in the regulation of water metabolism (see p. 391). E. The hypothalamus plays a role in controlling emotional states (see p. 391). 6. The following statements concern the third ventricle: (a) The posterior wall is formed by the opening into the cerebral aqueduct and the pineal recess. (b) It does not communicate directly with the lateral ventricles. (c) The vascular tela choroidea projects from the floor to form the choroid plexus. (d) Lying in the floor of the ventricle, from posterior to anterior, are the optic chiasma, the tuber cinereum, and the mammillary bodies. (e) The wall of the ventricle is not lined with ependyma. View Answer6. A is correct. The posterior wall of the third ventricle is formed by the opening into the cerebral aqueduct and the pineal recess (see Fig. 7-3). B. The third ventricle does communicate directly with the lateral ventricles through the interventricular foramina (see Fig. 7-14). C. The vascular tela choroidea projects from the roof of the third ventricle to form the choroid plexus (see Fig. 7-3). D. Lying in the floor of the third ventricle, from anterior to posterior, are the optic chiasma, the tuber cinereum, and the mammillary bodies (see p. 257). E. The wall of the third ventricle is lined with ependyma. Matching Questions. Directions: The following questions apply to Figure 7-30. Match the numbers listed on the left with the appropriate lettered structure listed on the right. Each lettered option may be selected once, more than once, or not at all. 7. Number 1 (a) Genu of corpus callosum (b) Interventricular foramen (c) Body of fornix (d) Anterior commissure (e) None of the above View Answer7. D is correct. 8. Number 2 (a) Genu of corpus callosum (b) Interventricular foramen (c) Body of fornix (d) Anterior commissure (e) None of the above View Answer8. A is correct. 9. Number 3 (a) Genu of corpus callosum (b) Interventricular foramen (c) Body of fornix (d) Anterior commissure (e) None of the above View Answer9. E is correct. The structure is the septum pellucidum. 10. Number 4 (a) Genu of corpus callosum (b) Interventricular foramen (c) Body of fornix (d) Anterior commissure (e) None of the above View Answer10. B is correct. 11. Number 5 (a) Genu of corpus callosum (b) Interventricular foramen (c) Body of fornix (d) Anterior commissure (e) None of the above View Answer11. C is correct. 12. Number 6 (a) Genu of corpus callosum (b) Interventricular foramen (c) Body of fornix (d) Anterior commissure (e) None of the above View Answer12. E is correct. The structure is the thalamus. 13. Number 7 (a) Genu of corpus callosum (b) Interventricular foramen (c) Body of fornix (d) Anterior commissure (e) None of the above View Answer13. E is correct. The structure is the splenium of the corpus callosum. Directions: Each of the numbered items in this section is followed by answers. Select the ONE lettered answer that is CORRECT. 14. The following statements concern the longitudinal cerebral fissure:

Figure 7-30 Sagittal section of the brain showing the medial surface of the diencephalon.

(a) The fissure contains the fold of dura mater, the falx cerebelli. (b) The fissure contains the middle cerebral arteries. (c) The superior sagittal sinus lies below it. (d) In the depths of the fissure, the corpus callosum crosses the midline. (e) The inferior sagittal sinus lies above it. View Answer14. D is correct. In the depths of the longitudinal cerebral fissure, the corpus callosum crosses the midline (see Fig. 7-6). A. The longitudinal cerebral fissure contains a fold of dura mater, the falx cerebri (see p. 428). B. The longitudinal cerebral fissure does not contain the middle cerebral arteries; they are located in the lateral cerebral fissures (see p. 475). C. The superior sagittal venous sinus lies above the longitudinal cerebral fissure (see p. 433). E. The inferior sagittal venous sinus lies in the lower border of the falx cerebri in the longitudinal cerebral fissure (see p. 433). 15. The following statements concern the central sulcus: (a) The central sulcus extends onto the medial surface of the cerebral hemisphere. (b) The frontal lobe lies posterior to it. (c) The parietal lobe lies anterior to it. (d) The central sulcus is continuous inferiorly with the lateral sulcus. (e) The arachnoid mater extends into the central sulcus. View Answer15. A is correct. The central sulcus extends onto the medial surface of the cerebral hemisphere (see Fig. 7-8). B. The frontal lobe lies anterior to the central sulcus (see Fig. 7-11). C. The parietal lobe lies posterior to the central sulcus (see Fig. 7-11). D. The central sulcus is not continuous inferiorly with the lateral sulcus (see Fig. 7-11). E. The arachnoid mater does not extend into the central sulcus (see p. 435). 16. The following statements concern the lateral ventricle: (a) Each ventricle is J shaped and filled with cerebrospinal fluid. (b) It communicates with the third ventricle through the interventricular foramen. (c) The body of the ventricle occupies the frontal lobe. (d) The lateral ventricle does not possess a choroid plexus. (e) The anterior horn occupies the parietal lobe. View Answer16. B is correct. The lateral ventricle communicates with the third ventricle through the interventricular foramen (see Fig. 7-3). A. Each lateral ventricle is C shaped and filled with cerebrospinal fluid (see Fig. 7-14). C. The body of the lateral ventricle occupies the parietal lobe (see p. 446). D. The lateral ventricle does possess a choroid plexus (see Fig. 7-1). E. The anterior horn of the lateral ventricle occupies the frontal lobe (see Fig. 7-14). 17. The following statements concern the corpus callosum: (a) It is connected to the fornix by the lamina terminalis. (b) The rostrum connects the genu to the septum pellucidum. (c) Most of the fibers within the corpus callosum interconnect symmetrical areas of the cerebral cortex. (d) The fibers of the genu curve forward into the frontal lobes as the forceps major. (e) The corpus callosum is related inferiorly to the falx cerebri. View Answer17. C is correct. Most of the fibers within the corpus callosum interconnect symmetrical areas of the cerebral cortex (see p. 265). A. The corpus callosum is connected to the fornix by the septum pellucidum (see Fig. 7-3). B. The rostrum of the corpus callosum connects the genu to the lamina terminalis (see Fig. 7-3). D. The fibers of the genu of the corpus callosum curve forward into the frontal lobes of the cerebral hemisphere as the forceps minor (see Fig. 7-16). E. The corpus callosum is related superiorly to the falx cerebri (see p. 257). 18. The following statements concern the anterior commissure: (a) It is embedded in the superior part of the septum pellucidum. (b) When traced laterally, an anterior bundle of fibers curves forward to join the olfactory tract. (c) Some of the fibers are concerned with the sensations of taste. (d) It forms the anterior boundary of the interventricular foramen. (e) It is formed by a large bundle of nerve fibers. View Answer18. B is correct. When the anterior commissure is traced laterally, an anterior bundle of nerve fibers is seen to curve forward to join the olfactory tract (see p. 265). A. The anterior commissure is embedded in the superior part of the lamina terminalis (see Fig. 7-3). C. Some of the fibers of the anterior commissure are concerned with the sensation of smell (see p. 265). D. The anterior boundary of the interventricular foramen is formed by the anterior pillar of the fornix and not the anterior commissure (see Fig. 7-3). E. The anterior commissure is formed by a small bundle of nerve fibers. 19. The following statements concerning the internal capsule are correct except: (a) It is continuous below with the tectum of the midbrain. (b) It has an anterior limb and a posterior limb, which are in a straight line. (c) The genu and the anterior part of the posterior limb contain the corticobulbar and corticospinal fibers. (d) It is related medially to the lentiform nucleus. (e) It is continuous below with the corona radiata. View Answer19. C is correct. The internal capsule contains the corticobulbar and corticospinal fibers in the genu and the anterior part of the posterior limb (see Fig. 7-18). A. The internal capsule is continuous below with the crus cerebri of the midbrain (see Fig. 7-20). B. The internal capsule is bent around the lentiform nucleus and has an anterior limb, a genu, and a posterior limb (see Fig. 7-18). D. The internal capsule is related laterally to the lentiform nucleus (see Fig. 7-18). E. The internal capsule is continuous above with the coronal radiata (see Fig. 7-20). 20. The following statements concern the basal ganglia:

Figure 7-31 Horizontal section of the cerebrum, as seen from above.

(a) The caudate nucleus is not attached to the lentiform nucleus. (b) The corpus striatum is concerned with muscular movement. (c) The lentiform nucleus is related medially to the external capsule. (d) The lentiform nucleus is oval shaped, as seen on horizontal section. (e) The amygdaloid nucleus does not form one of the basal ganglia. View Answer20. B is correct. The corpus striatum is concerned with the control of muscular movement (see p. 320). A. The head of the caudate nucleus is attached to the lentiform nucleus (see Fig. 7-15). C. The lentiform nucleus is related laterally to the external capsule (see Fig. 7-13). D. The lentiform nucleus is wedge shaped, as seen on horizontal section (see Fig. 7-13). E. The amygdaloid nucleus forms one of the basal ganglia (see p. 319). Matching Questions. Directions: The following questions apply to Figure 7-31. Match the numbers listed on the left with the appropriate lettered structure listed on the right. Each lettered option may be selected once, more than once, or not at all. 21. Number 1 (a) Optic radiation (b) Lateral sulcus (c) Lentiform nucleus (d) Anterior horn of lateral ventricle (e) None of the above View Answer21. E is correct. The structure is the genu of the corpus callosum. 22. Number 2 (a) Optic radiation (b) Lateral sulcus (c) Lentiform nucleus (d) Anterior horn of lateral ventricle (e) None of the above View Answer22. C is correct. 23. Number 3 (a) Optic radiation (b) Lateral sulcus (c) Lentiform nucleus (d) Anterior horn of lateral ventricle (e) None of the above View Answer23. E is correct. The structure is the posterior horn of the lateral ventricle. 24. Number 4 (a) Optic radiation (b) Lateral sulcus (c) Lentiform nucleus (d) Anterior horn of lateral ventricle (e) None of the above View Answer24. E is correct. The structure is the third ventricle. 25. Number 5 (a) Optic radiation (b) Lateral sulcus (c) Lentiform nucleus (d) Anterior horn of lateral ventricle (e) None of the above View Answer25. E is correct. The structure is the anterior column of the fornix. The following questions apply to Figure 7-32. Match the numbers listed on the left with the appropriate lettered structure listed on the right. Each lettered option may be selected once, more than once, or not at all. 26. Number 1 (a) Central sulcus (b) Postcentral gyrus (c) Superior temporal gyrus (d) Superior parietal lobule (e) None of the above View Answer26. E is correct. The structure is the middle frontal gyrus. 27. Number 2 (a) Central sulcus (b) Postcentral gyrus (c) Superior temporal gyrus (d) Superior parietal lobule (e) None of the above View Answer27. A is correct. 28. Number 3 (a) Central sulcus (b) Postcentral gyrus (c) Superior temporal gyrus (d) Superior parietal lobule (e) None of the above View Answer28. B is correct. 29. Number 4 (a) Central sulcus (b) Postcentral gyrus (c) Superior temporal gyrus (d) Superior parietal lobule (e) None of the above View Answer29. D is correct. 30. Number 5 (a) Central sulcus (b) Postcentral gyrus (c) Superior temporal gyrus (d) Superior parietal lobule (e) None of the above View Answer30. E is correct. The structure is the lateral sulcus. 31. Number 6 (a) Central sulcus (b) Postcentral gyrus (c) Superior temporal gyrus (d) Superior parietal lobule (e) None of the above View Answer31. C is correct. Directions: The case histories below are followed by questions. Select the ONE BEST lettered answer. A 70-year-old man with hypertension was admitted to an emergency department, having suddenly developed hemiparesis on the right side and numbness of the right leg. Axial CT and MRI were undertaken. MRI revealed a small hemorrhage in the left thalamus, which passed horizontally through the lateral ventricles. After careful observation, 2 days later the paresis was much improved, and the patient reported that his numbness had disappeared. The patient was discharged from the hospital 1 week later and made an uneventful recovery. His hypertension was brought under control with suitable medication.

Figure 7-32 Lateral view of the left cerebral hemisphere.

32. Using your knowledge of the relationships of the left thalamus, select the statement that explains the transient right hemiparesis and numbness. (a) The hemorrhage occurred into the third ventricle. (b) The hemorrhage into the thalamus extended laterally into the posterior limb of the left internal capsule. (c) The hemorrhage was small and confined to the thalamus on the left side. (d) The hemorrhage was small and occurred in the lateral part of the left thalamus, producing transient edema in the left internal capsule. (e) The hemorrhage extended laterally into the left lateral ventricle. View Answer32. D is correct. 33. This hypertensive patient had a small thalamic hemorrhage. Select the most likely cause for the hemorrhage: (a) One of the small diseased thalamic arteries may have ruptured. (b) One of the small veins draining the thalamus may have ruptured. (c) Vasoconstriction of the thalamic arteries could have occurred. (d) Softening of the neuronal tissue around the thalamic arteries might have taken place. (e) There is no relation between hypertension and the thalamic hemorrhage in this patient. View Answer33. A is correct. An 8-year-old boy with a severe earache on the right side was taken to a pediatrician. The symptoms had started 7 days ago, and the pain had progressively worsened. On examination, the boy was found to have severe right-sided otitis media with acute mastoiditis. On being questioned, the boy admitted that his head hurt badly all over and that he felt sick. While he was being examined, he vomited. His body temperature was slightly elevated. In view of the severity of the headache and the presence of nausea and vomiting, the pediatrician decided to have an MRI performed. The result showed a small, well-defined, right cerebral abscess. 34. The cerebral abscess in this patient was most likely located at which site in the right cerebral hemisphere: (a) Frontal lobe (b) Thalamus (c) Occipital lobe (d) Temporal lobe (e) Cuneus View Answer34. D is correct. P.283 Additional Reading Brzezinski, A. Melatonin in humans. N. Engl. J. Med. 336:186, 1997. Cassone, V. M. Effects of melatonin on vertebrate circadian systems. Trends Neurosci. 13:457, 1990. Clark, C. M., Ewbank, D., Lee, V. M. Y., and Trojanowski, J. Q. Molecular pathology of Alzheimer’s disease: Neuronal cytoskeletal abnormalities. In J. H. Growdon and M. N. Rossor (eds.), The Dementias: Blue Books of Practical Neurology (vol. 19, pp. 285–304). Boston: Butterworth-Heinemann, 1998. Crosby, E. C., Humphrey, T., and Lauer, E. W. Correlative Anatomy of the Nervous System. New York: Macmillan, 1962. Goetz, C. G. Textbook of Clinical Neurology (2nd ed.). Philadelphia: Saunders, 2003. Guyton, A. C., and Hall, J. E. Textbook of Medical Physiology (11th ed.). Philadelphia: Elsevier Saunders, 2006. Kawas, C. H. Early Alzheimer’s disease. N. Engl. J. Med. 349:1056–1063, 2003. Kehoe, P., Wavrant-De Vrieze, F., Crook, R., et al. A full genome scan for late onset Alzheimer’s disease. Hum. Mol. Genet. 8:237–245, 1999. Martin, J. B. Mechanisms of disease: Molecular basis of the neurodegenerative disorders. N. Engl. J. Med. 340:1970–1980, 1999. Marx, J. New gene tied to common form of Alzheimer’s disease. Science 281:507–509, 1998. Neve, R. L., and Robakis, N. K. Alzheimer’s disease: A re-examination of the amyloid hypothesis. Trends Neurosci. 21:15–29, 1998. Reiman, E. M., Caselli, R. J., Yun, L. S., Chen, K., Bandy, D., Minoshima, S., et al. Preclinical evidence of Alzheimer’s disease in persons homozygous for the epsilon 4 allele for apolipoprotein E. N. Engl. J. Med. 334:752, 1996. Rhoades, R. A., and Tanner, G. A. Medical Physiology. Boston: Little, Brown, 1995. Selkoe, D. J. Molecular pathology of Alzheimer’s disease: The role amyloid. In J. H. Growdon and M. N. Rossor (eds.), The Dementias: Blue Books of Practical Neurology (vol. 19, pp. 257–284). Boston: Butterworth-Heinemann, 1998. Snell, R. S. Effect of melatonin on mammalian epidermal melanocytes. J. Invest. Dermatol. 44:273, 1965. Standing, S. (ed.). Gray’s Anatomy (39th Br. ed.) London: Elsevier Churchill Livingstone, 2005. Swanson, L. W., and Sawchenko, P. E. Hypothalamic integration: Organization of the paraventricular and supraoptic nuclei. Annu. Rev. Neurosci. 6:269, 1983.

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