CN 3: Occulomotor Nerve

Question 1

Which muscles and functions does CN III control?

Answer 1

Superior rectus: elevation
Inferior rectus: depression
Medial rectus: adduction
Inferior oblique: external rotation

Question 2

What axon types is CN III?

Answer 2

General sensory efferent: oculomotor nucleus; move the eye

General visceral efferent: ciliary ganglion; parasympathetic

Question 3

At what level of the brainstem does the oculomotor nerve exit?

Answer 3

Rostral midbrain

Question 4

Define the movement of an impulse from the CN III nucleus to the eye muscles to constrict the pupil?

Answer 4

Nucleus (midbrain) -> edinger-Westphal nucleus -> ciliary ganglion -> pupillary constrictor muscles

Question 5

What are the four sets of neurons involved in the pupillary light reflex?

Answer 5

1. Afferent limb: retinal ganglion -> protectal nucleus (CN II)
2. EWN (CN III)
3. Preganglionic parasympathetic fibers to ciliary ganglion (CN III)
4. Ciliary nerves from ciliary ganglion supple muscles to constrict pupil (CN III)

Question 6

Injury to right eye cranial nerve three, light shines in that eye, what happens?

Answer 6

Due to intact CN II message gets back to Brainstem and tells pupils to constrict. Opposite eye will constrict since CN III is functional on that side.

Question 7

What happens to eye with ipsilateral lesion to CN III?

Answer 7

“Down and out”: Cannot move eye medially or vertically

Double vision

Pupil can stay large and near vision is affected