QS Study

The oculomotor nerve is the third of the cranial nerves and arises from the midbrain. It offers motor and parasympathetic innervation to many of the ocular structures. This nerve is responsible for eyeball and eyelid movement.

Functional components:

  • Somatic efferent.
  • General visceral efferent (parasympathetic).
  • General somatic afferent (propriocetive).

Location:

It is located in the anterior part of Gray matter that surrounds the cerebral aqueduct of the midbrain. It lies at the level of the superior colliculus.

Nuclei:

Oculomotor nucleus: Situated in the midbrain at the level of the superior colliculus.

Edinger Westphal nucleus: The fibers for constrictor pupillae & ciliaris arise here.

Oculomotor Nerve 1

Fig: Oculomotor Nerve

Course & distribution:

The oculomotor nerve originates from the anterior aspect of the midbrain. It moves anteriorly, passing below the posterior cerebral artery, and above the superior cerebellar artery. It passes forward between the posterior cerebral and superior cerebral arteries.

  1. The nerve emerges from the midbrain on the medial side of the crus cerebri.
  2. The nerve passes between the superior & posterior cerebral arteries & reaches the cavernous sinus.
  3. It enters the cavernous sinus by piercing its roof.
  4. In the anterior part of the sinus it divides into superior & inferior divisions.
  5. The two divisions enter the orbit through the middle part of superior orbital fissure.
  6. In the orbit, the upper divisions supplies the superior rectus & the levator palpebrae superioris.

The lower division divides into their branches for the medial rectus, inferior rectus & inferior oblique. The nerve passes through the two layers of the dura mater including the lateral wall of the cavernous sinus and then enters the superior orbital fissure to access the orbit.

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