Intro Brainstem I and II

Question 1

The midbrain arises from the ___.

Answer 1

Mesencephalon

Question 2

The pons and cerebellum form the _____, and arise from the____?

Answer 2

Metencephalon; Rhombencephelon (hindbrain)

Question 3

The medulla forms the ____, and arises from the ____.

Answer 3

Myelencephalon; Rhombencephalon (hindbrain)

Question 4

Which cranial nerves are responsible for eye movement?

Answer 4

(LR6SO4)3 Lateral Rectus 6 superior oblique 4, all others by 3

Question 5

What cranial nerve nuclei reside in the midbrain?

Answer 5

III, IV

III - Edinger Westphal nucleus

Question 6

What cranial nerve nuclei reside in the pons?

Answer 6

V, VI, VII, VIII

V - Mesephalic nucleus of V, Primary Motor nucleus of V, Main Sensory Nucleus of V, Spinal Nucleus of V (at caudal pons)

VIII (cochlear nucleus and vestibular nucleus at pontomedullary junction)

Question 7

What cranial nerve nuclei reside in the medulla?

Answer 7

IX, X, XII

IX - nucleus of solitary tract
X - (nucleus of solitary tract, dorsal motor nucleus of vagus and ventral motor nucleus of vagus aka nucleus ambiguous)
XII - (hypoglossal nucleus)
(Spinal nucleus of V is here too)

Question 8

There are 4 nuclei serving cranial nerve 5 in the Pons. What are their names, and what function does each serve?

Answer 8

Mesencephalic Nucleus of V - Proprioception
Main Motor nucleus of V - Motor
Main Sensory Nucleus of V - Fine touch, vibration
Spinal Nucleus of V - Pain and temp (the long one)

[Mesencephalic Nucleus of V is “stuck” in the pons, aka it would normally run with fine touch and proprioception, but is separated. Dr. Stabio mnemonic is the “earwax” in the kitty-cat’s ears.]

Question 9

What functions and cranial nerves does the solitary nucleus serve?

Answer 9

Taste from IX, VII, X

Question 10

Dorsal Motor Nucleus of Vagus

Answer 10

Motor vagal neurons to the larynx, pharynx (uvular deviation can signify damage). Also carries motor innervation to the stylopharyngeus which participates in swallowing and phonation.

Question 11

What fibers leave the nucleus ambiguous? Where are they bound?

Answer 11

Pre-ganglionic parasympathetic fibers depart the nucleus ambiguous for the heart and abdominal viscera (CN X).

Question 12

Hypoglossal Nucleus

Answer 12

x

Question 13

Where is the Edinger-Westphal nucleus in relation to nucleus of CN III? Where do these reside?

What information is processed in the EW nucleus? How is this tested clinically?

Answer 13

Both reside in the medial midbrain, rostral to the PAG. The nucleus of CN III is cone shaped. The EW nucleus looks like the “ice cream” on the “cone”. Remember that CN III exits the brainstem between the cerebral peduncles (through the interpeduncular fossa, between the posterior cerebral a. and the superior cerebellar a); this can help recall the location of the nucleus.

The EW nucleus is the parasympathetic pre-ganglionic nucleus that innervates the iris sphincter and the ciliary muscle (the synapse is in the ciliary ganglion). So the optic light response is the clinical test.

Question 14

Where is the CN IV nucleus?

Answer 14

Midbrain, rostral to the PAG, caudal to the nucleus of CN III, but in similar position.

Question 15

Corticobulbar tract

Answer 15

Carries motor information from the motor cortex to the nuclei of all the cranial nerves. Innervation is bilateral in all instances except two (lower of 7 and hypoglossal 12). This is why you don’t see a deficit from UMN lesion because the contralateral side can compensate.

[Bilateral UMN to 3, 4, 5, 6, Upper of 7, Nucleus Amb. ]

Consequence is that an UMN lesion of 7 will result in only the lower quadrant contralateral to the lesion drooping. In contrast, a LMN lesion (both nuclei or the entire facial nerve) the entire side of the face will by paralyzed (Bell’s palsy).