Occulomotor Nerve

STRUCTURE:
Midbrain

Third nerve nucleus( at the level of the superior colliculus ventral to the cerebral aqueduct, on the pre-aqueductal grey matter)

Red Nucleus

Substantia Nigra

Exit through Interpeduncular fossa

Invested with a sheath of pia mater

Passes between the superior cerebellar & posterior cerebral arteries (Nerve compressed by aneurysm of posterior communicating artery)

Pierces the dura mater

Pass b/w free and attached borders of tentorium cerebelli

Cavernous sinus

Receives filaments from the cavernous plexus of the sympathetic nervous system and communicating branch from V1

Superior orbital fissure

Orbit

Superior and Inferior Branch
BRANCHES OF OCCULOMOTOR NERVE:
Superior Branch
  • The superior branch of the oculomotor nerve or the superior division, the smaller, passes medially over the optic nerve.
  • It supplies the superior rectus and levator palpebrae superioris.
Inferior Branch
  • The inferior branch of the oculomotor nerve or the inferior division, the larger, divides into three branches.
  • One passes beneath the optic nerve to the medial rectus.
  • Another, to the inferior rectus.
  • The third and longest runs forward between the inferior recti and lateralis to the inferior oblique. 
  • From the last a short thick branch is given off to the lower part of the ciliary ganglion, and forms its short root.
NUCLEI:
  1. The oculomotor nucleus:
  • Originates at the level of the superior colliculus. 
  • The muscles it controls are the striated muscle in levator palpebrae superioris and all extraocular muscles except for the superior oblique muscle and the lateral rectus muscle.
  • 2. The Edinger-Westphal nucleus:
  • Supplies parasympathetic fibers to the eye via the ciliary ganglion, and thus controls the sphincter pupillae muscle (affecting pupil constriction) and the ciliary muscle 
  • (affecting accommodation).
  • All these branches enter the muscles on their ocular surfaces, with the exception of the nerve to the inferior oblique, which enters the muscle at its posterior border.
  • Sympathetic postganglionic fibres also join the nerve from the plexus on the internal carotid artery in the wall of the cavernous sinus and are distributed through the nerve, e.g., to the smooth muscle of superior tarsal (Mueller's) muscle.
FUNCTIONS:
  • The oculomotor nerve include axons of type GSE, general somatic efferent, which innervate skeletal muscle of the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique muscles.(innervates all the extrinsic muscles except superior oblique and lateral rectus.)
  • The nerve also includes axons of type GVE, general visceral efferent, which provide preganglionic parasympathetics to the ciliary ganglion.From the ciliary ganglion post 
  • ganglionic fibers pass through the short ciliary nerve to the constrictor pupillae of the iris and the cilliary muscles.

Exam Question
  • Nerve compressed by aneurysm of posterior communicating artery is occulomotor nerve
  • The muscles innervated by occulomotor nerve are superior rectus, levator palpebrae superioris ,medial rectus, inferior rectus & inferior oblique
  • Occulomotor nerve Carries parasympathetic nerve fibres to eye
  • Causes constriction of pupil is caused by occulomotor nerve
  • Cross section of midbrain at the level of superior colliculus shows 3rd CN & red nucleus

Don't Forget to Solve all the previous Year Question asked on Occulomotor Nerve