Book Review And Study Questions For Chapter 5

The corona radiata (radiating crown) are those fibers of the internal capsule that fan out in all directions from its superior edge. These fibers contain a variety of fibers traveling to and from the cerebral cortex. The superior longitudinal and uncinate fasciculi are organized bundles of corticocortical fibers on the ipsilateral side, and the cingulum is a fiber bundle located internal to the cingulate cortex. The fibers of the genu of the corpus callosum contain corticocortical fibers that pass between the cerebral hemispheres.(p.68–71,78)

The hippocampal formation, commonly called the hippocampus, is located in the medial wall of the temporal(inferior) horn of the lateral ventricle. Damage to the hippocampus may result in memory problems. The amygdaloid complex is located in the rostral wall of the temporal horn, the tail of the caudate in its lateral wall, and the calcar avis (also called the calcarine spur, a ridge in the wall of the posterior horn indicating the depth of the calcarine sulcus) is in the medial wall of the posterior horn of the lateral ventricle. The pulvinar is part of the diencephalon.(p.69–72,80)

These deficits are characteristic of Parkinson’s dis-ease and are directly correlated with loss of the dopamine (and melanin)-containing cells of the substantia nigra of the mid-brain. The locus (nucleus) ceruleus, also called the nucleus pigmentosus pontis, also contains cells with melanin, but loss of these cells does not cause motor deficits. The other choices do not contain pigmented cells, but damage to these structures does cause a different series of motor deficits.(p.70–71,80)

The anterior limb of the internal capsule is insinuated between the head of the caudate nucleus and the rostral aspect of the lenticular nucleus, mostly the putamen. The posterior limb is between the lenticular nucleus and the thalamus; the column of the fornix is rostromedial to the interventricular foramen; and the anterior commissure traverses the midline at the level of the genu of the internal capsule. The external capsule is a thin sheet of white matter lateral to the lenticular nucleus and medial to the claustrum.(p.66–67,78

The putamen is the most lateral part of the basal nuclei; taken together, the putamen and globus pallidus comprise the lenticular nucleus. The caudate nucleus, specifically its head and body portions, is located medial to the internal capsule. Although the subthalamic nucleus and the substantianigra function in concert with the basal nuclei, these structures are medially located and are not part of the basal nuclei.(p.69–70,78–79)

The pineal gland is located in the quadrigeminal cistern, superior to the colliculi, and between the pulvinar nuclei of the thalamus. At this location, the lesion would potentially impinge the colliculi and pulvinar. The other thalamic nuclei are not adjacent to the pineal, the globus pallidus is lateral to the posterior limb of the internal capsule, and the body of the caudate is located in the lateral wall of the body of the lateral ventricle.(p.73,79)

The nucleus accumbens is located in the rostral and basal forebrain at the point where the head of the caudate is continuous with the putamen. The amygdaloid nucleus is located internal to the uncus and in the anterior wall of the temporal horn. The pallidum (globus pallidus) and the substantia nigra do not have a continuum with the nucleus accumbens.(p.66,68,80)

Many of the fibers contained in the optic tract terminate in the lateral geniculate nucleus. Some of these fibers bypass this nucleus to traverse the brachium of the superior colliculus and a few enter the suprachiasmatic nucleus. The medial geniculate nucleus receives input via the brachium of the inferior colliculus (auditory); the pulvinar has interconnections with the visual cortex and superior colliculus; and the ventral posterolateral nucleus receives input from the anterolateral system and the medical lemniscus. The mammillary body is located rostral to the interpeduncular fossa and medial to the optic tract.(p.72,79,137,142)

The large bulge in the lateral wall of the anterior horn of the lateral ventricle is the head of the caudate nucleus. The position of the interventricular foramen represents the point at which the head of the caudate becomes the body of the caudate. The dorsomedial nucleus borders on the third ventricle; the anterior thalamic nucleus is located at the rostral end of the diencephalon and is caudomedial to the interventricularforamen; and the column of the fornix is rostromedial to thisforamen.(p.66–69,78)

The mammillothalamic tract extends from the mammillary bodies to the anterior nucleus of the thalamus; the cells of origin are in the mammillary nuclei and the axons terminate in the anterior nucleus. This tract is frequently visible in axial T2-weighted MRI. The ventral anterior nucleus is laterally adjacent to the mammillothalamic tract, but does not receive input from it. The other choices are nuclei located more caudally in the diencephalon.(p.69,78–88)

The posterior limb of the internal capsule, containing important cortical afferent and efferent fibers, is located between the lenticular nucleus and dorsal thalamus. Damage to this structure may result in sensory and/or motor deficits on the opposite side of the body. The anterior limb is located between the head of the caudate and putamen, while the retro-lenticular limb is found caudal to the lenticular nucleus. The crus cerebri is on the inferolateral aspect of the midbrain. The external capsule is lateral to the putamen.(p.67,70,79,80)

The geniculate bodies are tucked-up under the caudal and inferior aspect of the pulvinar. The groove between the medial geniculate body and pulvinar contains the brachium of the superior colliculus. The geniculate bodies and the pulvinar have a common blood supply from the thalamogeniculate artery, a branch of P2 . None of the other choices have a close apposition with the geniculate bodies. The anterior thalamic, rostral dorsomedial, and subthalamic nuclei do not share a common blood supply with the pulvinar.(p.72,79)

The amygdaloid complex is located immediately internal to the uncus. Bilateral damage to rostral portions of the temporal lobe may include the amygdala and result in a constellation of deficits known as the Klüver-Bucy syndrome. The hippocampal formation is internal to the cortex of the parahippocampal gyrus, and the anterior thalamic nucleus is internal to the anterior thalamic tubercle. The cingulate gyrusoverlies the longitudinally oriented fibers of the cingulum and the grackle tubercle is the external elevation formed by the gracile nucleus.(p.67–68,80)

The layer of white matter located internal to the insular cortex, and external to the claustrum, is the extreme capsule. The external capsule is found between the claustrum and the putamen, and the internal capsule is a large bundle of fibers located primarily between the lenticular nucleus on one side and the head of the caudate and the diencephalon on the other side. The tapetum is located in the lateral wall of the posterior horn of the lateral ventricle. Arcuate fasciculi are small bundles of fibers passing between gyri.(p.69–70,78–79)

The hippocampal commissure is located immediately inferior to the splenium of the corpus callosum; the crossing of these fibers takes place at this point. Other parts of the corpus callosum are not related to the hippocampal commissure, and the spiral fibers of the hippocampus are bundles within the
hippocampal formation in the temporal lobe. Some of the fibers in the hippocampal commissure enter the precommissural fornix, but by no means all.(p.74)

The internal medullary lamina is a vertically oriented sheet of fibers that extends from the rostral portion of the thalamus caudally to surround the centromedian nucleus; this nucleus is frequently referred to as “in “the internal medullary lamina due to its position. This lamina separates the dorsomedial nucleus from the laterally adjacent ventral anterior, ventral lateral, and ventral posterolateral nuclei. The external medullary lamina is located between the thalamus and the posterior limb of the internal capsule, and the lamina terminalis is the rostral wall of the third ventricle. The stria medullaris is a small bundle of fibers passing rostrocaudally along the upper medial edge of the thalamus from the general location of the interventricular foramen to the habenula, and the ansa lenticularis contains pallidothalamic fibers.(p.69–71,78)

The subthalamic nucleus is separated from the substantia nigra by only a thin layer of myelinated fibers; these two structures are directly adjacent to each other. Damage to the subthalamic nucleus gives rise to hemiballistic movements(described in this question) while loss of cells in the substantianigra results in the motor deficits seen in Parkinson’s disease. The putamen, globus pallidus, and the medial geniculate nucleus are all lateral to the internal capsule; the subthalamic nucleus is medial. The centromedial nucleus is separated from the subthalamic nucleus by other thalamic nuclei.(p.70,71,80)

The column of the fornix is that portion of this fiber bundle that arches around the rostromedial end of the thalamus. As it does so, the column joins its counterpart on the opposite side and “leans against “the anterior commissure. The column of the fornix also signifies, in cross section or axial planes, the laterally adjacent interventricular foramen andgenu of the internal capsule. The mammillothalamic tract is located caudal to the fornix, and the crus of the fornix is found along the midline superior to the thalamus. The anterior limb of the internal capsule is found between the head of the caudate nucleus and the lenticular nucleus (mainly the putamen).The lenticular fasciculus contains pallidothalamic fibers and traverses the posterior limb of the internal capsule en route to the dorsal thalamus.(p.67–68,70,78–79)

The anterior commissure, as it passes laterally from the midline, separates the dorsal basal nuclei (putamen and Globus pallidus) from the ventral striatum and ventral pallidum. The posterior commissure is located at the caudal aspect of the third ventricle just above the opening of the cerebral aqueduct, and the Massa intermedia bridges the third ventricle in about 80% of individuals; in about 20% it is absent. The rostral wall of the third ventricle is formed by the lamina terminals and the septum pellucidum forms the medial wall of the anterior horn of the lateral ventricle.(p.67,79)

The optic radiations are located in the lateral wall of the posterior horn of the lateral ventricle as they pass through the retro lenticular limb of the internal capsule from the lateral geniculate nucleus to the primary visual cortex. A thin layer of white matter, the tapetum, separates the optic radiations from the wall of the ventricle. The cisterns at the midbrain on the basal aspect of the hemisphere contain the optic tract. The other ventricular spaces listed have no direct relationship to the optic radiations.(p.74,78–79)