Oculomotor nerve (CN III)
The oculomotor nerve is the third of the cranial nerves and arises from the midbrain. It is responsible for some eye movements.
Nucleus and cisternal portion
Exiting the midbrain in the interpeduncular cistern the nerve travel forwards, below the posterior cerebral artery (where it can be compressed by a posterior communicating artery aneurysm) and above the superior cerebellar artery, before piercing the dura mater and entering the cavernous sinus.
Cavernous sinus portion
Within the cavernous sinus the oculomotor nerve is located uppermost, above the trochlear nerve in the lateral wall of the sinus.
Orbital portion
It enters the orbit via the superior orbital fissure as two branches: superior division and inferior division, with the nasociliary nerve (a branch of the ophthalmic nerve) between them and the abducens nerve (CN VI) below all three. These four branches pass through the tendinous ring.
Superior division
The superior division, the smaller of the two, runs above the optic nerve and gives branches to superior rectus and levatore palpebrae muscle which it supplies with motor fibres. Additionally it also supplies the later with sympathetic fibres which it picked up from the internal carotid artery.
Inferior division
The inferior division supplies the inferior rectus, medial rectus (this branch passes below the optic nerve), and the inferior oblique. It also gives off the parasympathetic root to the ciliary ganglion.
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