CHAPTER 10

Question 1

1. All of the following statements concerning
   the spinal trigeminal tract are correct EX-
   CEPT
   (A) it contains axons from the trigeminal gan-
   glion
   (B) it mediates pain and temperature sensa-
   tion
   (C) it is equivalent to the dorsolateral tract of
   Lissauer
   (D) it is the afferent limb of the jaw jerk reflex
   (E) it extends from C3 to a midpontine level

Answer 1

l-D. The afferent limb of the jaw jerk reflex, a myotatic (muscle stretch) reflex, is mediated by
the pseudounipolar neurons of the mesencephalic nucleus; the efferent limb is mediated by the
motor neurons of the trigeminal motor nucleus.

Question 2

2. All of the following statements concerning
   the ventral trigeminothalamic tract are correct
   EXCEPT
   (A) it transmits pain and temperature infor-
   mation
   (B) it consists of axons from the spinal
   trigeminal nucleus
   (C) it receives axons from the principal sen-
   sory nucleus of CN V
   (D) it projects to the contralateral ventral
   posteromedial (VPM) nucleus of the thal-
   amus
   (E) first-order neurons are located in the mes-
   encephalic nucleus

Answer 2

2-E. The mesencephalic nucleus does not contribute to the ventral trigeminothalamic tract. The
ventral trigeminothalamic tract consists of axons from the spinal trigeminal nucleus that trans-
mit pain and temperature information to the contralateral ventral posteromedial (VPM) nucleus.
In addition, it receives and transmits tactile discriminatory input from the principal sensory nu-
cleus of CN V to the VPM nucleus.

Question 3

3. An aneurysm of the cavernous sinus could
   result in all of the following EXCEPT
   (A) ptosis
   (B) anesthesia of the tongue
   (C) paralysis of the superior oblique muscle
   (D) complete internal ophthalmoplegia
   (E) diplopia

Answer 3

3-B. An aneurysm of the cavernous sinus would not involve the mandibular nerve (CN V-3),
which does not pass through the wall of the sinus. The mandibular nerve provides the sensory
innervation of the anterior two-thirds of the tongue. Involvement of the oculomotor nerve (CN
III), if complete, would result in internal ophthalmoplegia because of interruption of pregan-
glionic parasympathetic fibers (a fixed, dilated, unresponsive pupil).

Question 4

4. All of the following statements concerning
   trigeminal neuralgia are correct EXCEPT
   (A) it is characterized by recurrent parox-
   ysms of sharp, lancinating pain
   (B) it occurs in any of the three divisions of
   the trigeminal nerve
   (C) it usually occurs in people over 50 years of
   age
   (D) it is more common in men than in women
   (E) it may result from pressure on the nerve
   from a nearby artery

Answer 4

4-D. Trigeminal neuralgia is more common in women than in men, and it occurs most often on
the right side of the face. A redundant loop of the superior cerebellar artery may impinge on the
trigeminal nerve, causing electric “chatter,” which is felt as pain. This type of trigeminal neu-
ralgia has been successfully treated by placing a small sponge between the artery and the nerve.
Classic idiopathic trigeminal neuralgia is treated with carbamazepine, an anticonvulsant drug.

Question 5

5. All of the following statements concerning
   the trigeminal ganglion are correct EXCEPT
   (A) it lies in the Meckel cave
   (B) it lies in the middle cranial fossa
   (C) it contains bipolar ganglion cells
   (D) it contains first-order neurons of the dor-
   sal trigeminothalamic tract
   (E) its destruction results in abolition of the
   corneal reflex and the jaw jerk reflex

Answer 5

5-C. The trigeminal (gasserian) ganglion lies within a dural duplication, the Meckel cave, lo-
cated in the trigeminal fossa of the petrous portion of the temporal bone in the middle cranial
fossa. It contains pseudounipolar ganglion cells similar to those found in the dorsal root ganglia.
These first-order neurons give rise to the ventral and dorsal trigeminothalamic tracts. Destruc-tion of the trigeminal ganglion interrupts the afferent limbs of the corneal (CN V-l) and jaw jerk (CN V-3) reflexes. The motor root of CN V lies between the ganglion and the petrous bone.

Question 6

6. All of the following statements concerning
   the maxillary nerve are correct EXCEPT
   (A) it runs in the lateral wall of the cavernous
   sinus
   (B) it exits the cranial vault via the foramen
   rotundum
   (C) it contains only general somatic afferent
   (GSA) fibers
   (D) it innervates the skin of the dorsum of the
   nose
   (E) it innervates the palate

Answer 6

6-D. The maxillary nerve (CN V-2) contains only general somatic afferent (GSA) fibers, runs in the lateral wall of the cavernous sinus, and exits the cranial vault via the foramen rotundum and canalis rotundus. It innervates the palate via the palatine nerves. The dorsum of the nose is in-nervated by the ophthalmic nerve (CN V-l).

Question 7

7. All of the following statements concerning
   the mesencephalic nucleus are correct EX-
   CEPT
   (A) it projects to the cerebellum
   (B) it is located in the pons
   (C) it mediates the afferent limb of the jaw
   jerk reflex
   (D) it contains bipolar neurons
   (E) it receives input from muscle spindles

Answer 7

7-D. The mesencephalic nucleus of CN V contains pseudounipolar neurons that mediate the af-
ferent limb of the jaw jerk reflex. It is located in the rostral pons and in the mesencephalon and
gives rise to collaterals that project to the cerebellum via the superior cerebellar peduncle. It re-
ceives input from muscle spindles and pressure and joint receptors.

Question 8

8. All of the following statements concerning
   the dorsal trigeminothalamic tract are correct
   EXCEPT
   (A) it is an uncrossed tract
   (B) it mediates two-point tactile discrimina-
   tion
   (C) it mediates the corneal reflex
   (D) it projects to the ventral posteromedial
   (VPM) nucleus of the thalamus
   (E) its first-order neurons are found in the
   trigeminal ganglion

Answer 8

8-C. The dorsal trigeminothalamic tract mediates discriminative tactile and pressure sensation
(including two-point discrimination), is an uncrossed tract, and projects to the ventral postero-medial (VPM) nucleus. First-order neurons are in the trigeminal ganglion, second-order neurons lie in the principal sensory nucleus of the rostral pons, and third-order neurons are located in the VPM nucleus of the thalamus. This tract corresponds in function to the dorsal column-medial lemniscus system. The dorsal trigeminothalamic tract does not mediate the corneal reflex.

Question 9

9. All of the following statements concerning
   the principal sensory nucleus of CN V are cor-
   rect EXCEPT
   (A) it projects to the ipsilateral ventral pos-
   teromedial (VPM) nucleus of the thala-
   mus
   (B) it projects to the contralateral VPM nu-
   cleus of the thalamus
   (C) it receives input from Meissner and
   Pacini corpuscles
   (D) it is located in the medulla and pons
   (E) it is a homolog to the dorsal column nuclei

Answer 9

9-D. The principal sensory nucleus of CN V is located in the rostral pons at the level of the motor trigeminal nucleus; it receives input from Meissner and Pacini corpuscles. It projects to the ipsilateral ventral posteromedial (VPM) nucleus of the thalamus via the dorsal trigeminothalamic tract and to the contralateral VPM nucleus of the thalamus via the ventral trigeminothalamic tract. The principal sensory nucleus is homologous to the dorsal column nuclei (gracile and
cuneate nuclei).

Question 10

10. All of the following statements concerning
    the trigeminal nerve are correct EXCEPT
    (A) it is the nerve of the first branchial arch
    (mandibular nerve)
    (B) it contains only general somatic afferent
    (GSA) and somatic visceral efferent (SVE)
    fibers
    (C) it innervates the stapedius muscle
    (D) it innervates the dura of the anterior and
    middle cranial fossae
    (E) it mediates the afferent limb of the corneal
    reflex

Answer 10

10-C. The trigeminal nerve (CN V) is the nerve of the first branchial arch (mandibular nerve) and contains only general somatic afferent (GSA) and special visceral efferent (SVE) fibers. It in-nervates the supratentorial dura of the anterior and middle cranial fossae. The dura of the posterior cranial fossa is innervated by the vagal nerve (CN X) and the second and third spinal nerves
(C2 and C3), which hitchhike with the hypoglossal nerve (CN XII). The tensor tympani muscle is innervated by the trigeminal nerve; the stapedius muscle is innervated by the facial nerve (CN VII). The ophthalmic nerve (CN V-l) mediates the afferent limb of the corneal reflex; the facial
nerve (CN VII) mediates the efferent limb of the corneal reflex (orbicularis oculi muscle).

Question 11

11. All of the following lesions could interrupt
    the corneal reflex EXCEPT
    (A) occlusion of the anterior inferior cerebel-
    lar artery
    (B) occlusion of the posterior inferior cerebel-
    lar artery
    (C) an acoustic neuroma
    (D) an aneurysm of the cavernous sinus
    (E) destruction of the principal sensory nu-
    cleus of CN V

Answer 11

11-E. The principal sensory nucleus of CN V mediates tactile discriminatory sense and position
sense, homologous to the gracile and cuneate nuclei. The anterior and posterior inferior cerebel-
lar arteries both interrupt the afferent corneal pathway as may an aneurysm of the cavernous
sinus. An acoustic neuroma interrupts the efferent limb of the corneal reflex (CN VII).

Question 12

12. All of the following statements concerning
    the corneal reflex are correct EXCEPT
    (A) it is a bisynaptic reflex
    (B) it is abolished ipsilaterally by transection
    of the facial nerve
    (C) it is abolished by a transection of the
    spinal trigeminal tract made within its
    caudal medullary extent
    (D) it is mediated via axons found in the
    spinal trigeminal tract
    (E) it is mediated via axons arising from the
    spinal trigeminal nucleus

Answer 12

12-C. The afferent corneal reflex pathway is as follows: First-order neurons of the ophthalmic
nerve (CN V-l) are found in the trigeminal ganglion. Their axons enter the pons and descend in
the spinal trigeminal tract. They enter the spinal trigeminal nucleus in its rostral portion and
synapse on second-order neurons, which project to the ipsilateral and contralateral facial nuclei.
Axons from third-order neurons in the facial nuclei innervate the orbicularis oculi muscles bi-
laterally (directly and consensually). Trigeminal tractotomy at caudal levels produces facial
anesthesia without interruption of the corneal reflex