Oculomotor Nerve Flashcards

Explore the oculomotor nerve's midbrain origins, anatomical course, muscular branches, parasympathetic pathways, and clinical lesions.

Card 1 of 30Question

What is the numerical designation of the oculomotor nerve?

Cranial nerve III (CN III).

In This Section

1. What is the numerical designation of the oculomotor nerve?

Cranial nerve III (CN III).

2. What are the two functional components of the oculomotor nerve?

General somatic efferent motor fibers and general visceral efferent parasympathetic fibers.

3. Where is the oculomotor nucleus located?

In the rostral midbrain at the level of the superior colliculus, near the cerebral aqueduct.

4. Which midbrain nucleus provides preganglionic parasympathetic fibers to the oculomotor nerve?

The Edinger-Westphal nucleus.

5. From which surface of the brainstem does the oculomotor nerve emerge?

The ventral surface of the midbrain, within the interpeduncular fossa.

6. Between which major arteries does the oculomotor nerve pass after emerging from the midbrain?

Between the posterior cerebral artery and superior cerebellar artery.

7. Which artery lies close to the oculomotor nerve near its junction with the internal carotid artery?

The posterior communicating artery.

8. Through which dural region does the oculomotor nerve enter the cavernous sinus?

It pierces the dura near the posterior clinoid process and enters the lateral wall of the cavernous sinus.

9. Where is the oculomotor nerve positioned within the lateral wall of the cavernous sinus?

Superior to the trochlear nerve and the ophthalmic and maxillary divisions of the trigeminal nerve.

10. Through which opening does the oculomotor nerve enter the orbit?

The superior orbital fissure.

11. What is the relationship of the oculomotor nerve to the common tendinous ring?

Its superior and inferior divisions pass through the common tendinous ring.

12. Into which two divisions does the oculomotor nerve divide near the orbital apex?

The superior division and inferior division.

13. Which muscles are supplied by the superior division of the oculomotor nerve?

The superior rectus and levator palpebrae superioris muscles.

14. Which extraocular muscles are supplied by the inferior division of the oculomotor nerve?

The medial rectus, inferior rectus, and inferior oblique muscles.

15. Which two extraocular muscles are not innervated by the oculomotor nerve?

The superior oblique, supplied by cranial nerve IV, and lateral rectus, supplied by cranial nerve VI.

16. What is the primary action of the medial rectus muscle?

Adduction of the eyeball.

17. Which oculomotor-innervated muscle primarily elevates the upper eyelid?

The levator palpebrae superioris muscle.

18. Through which branch do preganglionic parasympathetic fibers reach the ciliary ganglion?

The nerve to the inferior oblique muscle, a branch of the inferior division of cranial nerve III.

19. Where is the ciliary ganglion located?

In the posterior orbit, between the optic nerve and lateral rectus muscle.

20. Which nerves carry postganglionic parasympathetic fibers from the ciliary ganglion to the eyeball?

The short ciliary nerves.

21. What is the parasympathetic action of the oculomotor nerve on the iris?

Contraction of the sphincter pupillae muscle, producing pupillary constriction.

22. How does the oculomotor nerve contribute to accommodation for near vision?

It stimulates the ciliary muscle, reducing zonular tension and allowing the lens to become more convex.

23. What role does the oculomotor nerve play in the pupillary light reflex?

It forms the efferent limb, carrying parasympathetic signals that constrict the pupil.

24. What is the typical resting position of the eye in complete oculomotor nerve palsy?

Deviated downward and outward due to unopposed lateral rectus and superior oblique activity.

25. Why does complete oculomotor nerve palsy cause ptosis?

Paralysis of the levator palpebrae superioris muscle.

26. What pupillary abnormality can result from damage to the parasympathetic fibers of cranial nerve III?

Ipsilateral pupillary dilation (mydriasis) with impaired light response.

27. Which vascular lesion can compress the oculomotor nerve and produce a dilated pupil?

An aneurysm of the posterior communicating artery near its junction with the internal carotid artery.

28. Why may an ischemic oculomotor nerve palsy initially spare pupillary function?

The superficial parasympathetic fibers may remain intact when central somatic motor fibers are ischemic.

29. Which descending brain displacement can compress the oculomotor nerve against the tentorial edge?

Uncal herniation.

30. What type of diplopia commonly occurs with oculomotor nerve palsy?

Binocular diplopia caused by misalignment of the visual axes, often with horizontal and vertical components.