Answers To Clinically Based Questions morphology of the brain Part 1
Answers to clinically based questions
1. Answer B: Numbness on the face, resulting from a lesion in the cerebral cortex,
indicates a lesion in the lower one-third of the postcentral gyrus (face area of the
somatosensory cortex). The anterior paracentral gyrus and the precentral gyrus are
somatomotor areas of the cerebral cortex. The upper extremity is represented in the
middle one-third of the postcentral gyrus and the lower extremity is represented in
the posterior paracentral gyrus.
2. Answer D: Tic douloureux (trigeminal neuralgia) is agonizing pain that originates
from the branches of the trigeminal nerve, primarily its V2 or V3 territories. The
trigger zone is frequently around the corner of the mouth. There is a geniculate
neuralgia (related to the ear) and a glossopharyngeal neuralgia (related to the throat),
but neither of these originates from the surface of the face near the oral cavity. The
hypoglossal nerve is the motor for the tongue and the vagus is the motor for most of
the pharynx and larynx, visceromotor for much of the gut, and contains
viscerosensory fibers from the gut.
3. Answer A: In most cases (85–100%), the labyrinthine artery, also called the
internal auditory artery, originates from the anterior inferior cerebellar artery (a
branch from the basilar artery). It enters the internal acoustic meatus, serves bone
and dura of the canal, the nerves of the canal, and vestibular and cochlear structures.
In a few cases (15% or less), this artery originates from the basilar artery. None of
the other choices gives rise to vessels that serve the inner ear.
4. Answer E: The quadrigeminal artery is the primary blood supply to the superior
and inferior colliculi: this vessel originates from posterior cerebral artery. The
geniculate bodies receive their blood supply from the thalamogeniculate arteries, and
the pineal and habenula from the posterior medial choroidal artery. The superior
cerebellar peduncle receives its blood supply via the medial branch of the superior
cerebellar artery, and branches of the cerebral circle (of Willis) supply the
5. Answer C: Vestibular schwannomas larger than 2.0 cm in diameter may impinge
on the root of the trigeminal nerve and cause numbness on the same side of the face.
Although the other deficits listed are not seen in these patients, diplopia
(involvement of oculomotor, abducens or trochlear nerves, singularly or in
combination) may be present, but in fewer than 10% of these individuals.
6. Answer B: The internal acoustic meatus contains the vestibulocochlear nerve, the
facial nerve, and the labyrinthine artery, a branch of the anterior inferior cerebellar
artery. A vestibular schwannoma located in the meatus would likely affect the facial
nerve and result in facial weakness. The vagus and glossopharyngeal nerves exit the
skull via the jugular foramen (along with the accessory nerve). The cerebellar
arteries originate within the skull and distribute to structures within the skull.
(The so-called acoustic neuroma, a tumor associated with the eighth nerve, is
actually a vestibular schwannoma since it arises from the neurilemma sheath
of the vestibular root. Most patients with this tumor have hearing loss, tinnitus
and equilibrium problems, or vertigo. As the tumor enlarges (to more than
about 2 cm) it may cause facial weakness (seventh nerve root), numbness
(fifth nerve root), or abnormal corneal reflex (fifth or seventh nerve roots).
Treatment is usually by surgery, radiation therapy, or a combination thereof.)
7. Answer C: The lingual gyrus is the lower bank of the calcarine sulcus; the upper
(cuneus) and lower banks (lingual) of this sulcus are the location of the primary
visual cortex. The precuneus is the medial aspect of the parietal lobe, and the
angular gyrus is a portion of the inferior parietal lobule on the lateral aspect of the
hemisphere. The cingulated and parahippocampal gyri are located on the medial
aspect of the hemisphere and are parts of the limbic lobe.
8. Answer A: The cerebral aqueduct is about 1.5–2.0 mm in diameter, and connects
the third ventricle with the fourth ventricle. When this part of the ventricular system
appears in a sagittal MRI, the plane of the scan is at the midline. Neither the
interventricular foramen nor the superior colliculus are on the midline. Both the
interpeduncular fossa and the corpus callosum are on the midline, but extend off the
midline well beyond the width of the cerebral aqueduct.
9. Answer A: The only portion of the ventricular system that does not contain
choroid plexus is the cerebral aqueduct. The choroids plexus in the lateral ventricle
is continuous from the inferior horn into the atrium and into the body of the
ventricle, and through the interventricular foramen with the choroid plexus located
along the roof of the third ventricle. There is a tuft of choroid plexus in the fourth
ventricle, a small part of which extends into the lateral recess and through the lateral
foramen (of Luschka) into the subarachnoid space at the cerebellopontine angle.
10. Answer E: Branches of the superior cerebellar artery are most frequently
involved in cases of trigeminal neuralgia that are presumably of vascular origin. The
posterior cerebral artery and its larger branches serve the midbrain-diencephalic
junction or join the medial surface of the hemisphere. The basilar artery serves the
basilar pons and the anterior inferior cerebellar artery serves the caudal midbrain,
inner ear, and the inferior surface of the cerebellar surface. The basal vein drains the
medial portions of the hemisphere and passes through the ambient cistern to join the
great cerebral vein (of Galen).
11. Answer C: The afferent limb of the corneal reflex is via the ophthalmic division
of the trigeminal nerve (V); the cell body of origin is in the trigeminal ganglion and
the central terminations in the pars caudalis of the spinal trigeminal nucleus. The
efferent limb originates in the motor nucleus of the facial nerve (VII) and distributes
to the facial muscles around the eye. None of the other choices contains fibers
related to the corneal reflex.
12. Answer B: The callosomarginal artery, a branch of the anterior cerebral artery,
supply the medial aspect of the superior frontal gyrus and that portion of this gyrus
on the superior and lateral aspects of the hemisphere. The middle cerebral artery
serve the lateral aspects of the hemisphere; the posterior cerebral artery serve the
medial aspects of the hemisphere caudal to the parietoccipital sulcus, and the angular
artery (branch of middle cerebral artery) serves the angular gyrus of the inferior
parietal lobule. The lenticulostriate arteries are branches of middle cerebral that
supply the internal structures of the hemisphere.
13. Answer B: The limbic lobe, consisting primarily of the cingulated gyrus and the
parahippocampal gyrus, is located on the most medial aspect of the hemisphere; the
cingulate gyrus is located immediately adjacent to the corpus callosum. None of the
other lobes of the cerebral cortex borders directly on the corpus callosum.
14. Answer B: The inferior frontal gyrus consists of the pars orbitalis (Brodmann
area 47), pars triangularis (area 45), and pars opercularis (area 44). A lesion located
primarily in areas 44 and 45 (in the inferior frontal gyrus) in the dominant
hemisphere will result in a nonfluent (Broca) aphasia. The supramarginal (area 40)
and angular (area 39) gyri represent what is called the Wernicke area. The middle
frontal gyrus contains areas 6 and 8. The lower lateral one-third of the precentral
gyrus is the face area of the somatomotor cortex.
15. Answer A: Areas 3, 1, 2 collectively represent the somatosensory cortex. Area 4
is the primary somatomotor cortex, area 17 the primary visual cortex, and area 22
the primary auditory cortex. Area 40 is in the supramarginal gyrus, a large part of
which is called the Wernicke area.
16. Answer B: The body is represented in the somatomotor cortex (precentral gyrus,
anterior paracentral gyrus) in the following pattern: the face in about the lower one-
third of the precentral gyrus above the lateral sulcus; the hand and upper extremity
in about its middle third; and the trunk and hip in about its upper third. The lower
extremity and foot are represented in the anterior paracentral gyrus. Posterior
portions of the middle frontal gyrus are the location of the frontal eye field.
17. Answer C: The L4-L5 interspace is commonly used for a lumbar puncture. The
L3-L4 space may also be used. Levels T12 to L2-L3 are too high. Because the
caudal end of the spinal cord (the conus medullaris) may be as low as L2 in some
individuals, levels. T12-L1 to L2-L3 are not used, as this would most likely result in
damage to the spinal cord. The S1-S2 vertebrae are fused so there is no
intervertebral space through which a needle can pass. Furthermore, the dural sac
ends at about S2.
18. Answer B: The oculomotor nerve (III) exits from the medial aspect of the
midbrain into the interpeduncular fossa/cistern. It traverses this space, courses
through the lateral wall of the cavernous sinus to eventually enter (along with the
trochlear [IV] and abducens [VI] nerves) the superior orbital fissure. Cranial nerves
IV, VI, and V1 (the ophthalmic portion of the trigeminal nerve), along with III, pass
through the cavernous sinus. Cranial nerve II (optic) is quite rostral to the
19. Answer D: A lesion in area 44 that spreads will affect the lower portions of the
precentral gyrus in which the face is represented. This will result in weakness of
facial muscles, accompanied by other cranial nerve deficits. The cortical areas for
hearing and vision are far separated from area 44. Also, a lesion in the primary
auditory cortex will not result in a hearing loss in one ear. The hand area of the
sensory cortex and the upper extremity area of the motor cortex are not adjacent to
Brodmann area 44.
20. Answer A: As they descend in the dural sac from their origin from the spinal
cord to their exit at their respective intervertebral foramen, the anterior and posterior
roots form the cauda equina. The conus medullaris is the most caudal end of the
spinal cord, and the filum terminale internum is the strand of pia that extends from
the conus caudally to attach to the inner aspect of the dural sac at about S2. The
denticulate ligament anchors the spinal cord laterally to the inner surface of the dural
sac, and the filum terminale externum anchors the dural sac caudally to the inner
aspect of the coccyx.