2. OCULOMOTOR NERVE
CN III: OVERVIEW
▸ The oculomotor nerve is the third cranial nerve (CN III)
▸ It provides motor and parasympathetic innervation to some of the structures
within the bony orbit
▸ Motor – Innervates the majority of the extraocular muscles (levator
palpebrae superioris, superior rectus, inferior rectus, medial rectus and
inferior oblique)
▸ Parasympathetic – Supplies the sphincter pupillae and the ciliary muscles
of the eye
▸ Sympathetic – No direct function, but sympathetic fibres run with the
oculomotor nerve to innervate the superior tarsal muscle (helps to raise
the eyelid)
3. OCULOMOTOR NERVE
CN III: ANATOMICAL COURSE
▸ The oculomotor nerve originates from the oculomotor nucleus
▸ located within the midbrain of the brainstem, ventral to the cerebral aqueduct
▸ It emerges from the anterior aspect of the midbrain, passing inferiorly to the
posterior cerebral artery and superiorly to the superior cerebellar artery
▸ The nerve then pierces the dura mater and enters the lateral aspect of
the cavernous sinus
▸ Within the cavernous sinus, it receives sympathetic branches from the internal
carotid plexus
▸ These fibres do not combine with the oculomotor nerve – they merely travel within
its sheath
4. OCULOMOTOR NERVE
CN III: ANATOMICAL COURSE
▸ The nerve leaves the cranial cavity via the superior orbital fissure
▸ At this point, it divides into superior and inferior branches:
▸ Superior branch – provides motor innervation to the superior rectus and
levator palpabrae superioris
▸ Sympathetic fibres run with the superior branch to innervate the superior
tarsal muscle
▸ Inferior branch – provides motor innervation to the inferior rectus, medial
rectus and inferior oblique
▸ Also supplies pre-ganglionic parasympathetic fibres to the ciliary
ganglion, which ultimately innervates the sphincter pupillae and ciliary
muscles
7. OCULOMOTOR NERVE
CN III: MOTOR FUNCTIONS
▸ The oculomotor nerve innervates many of the extraocular
muscles
▸ These muscles move the eyeball and upper eyelid
▸ Inferior Branch:
▸ Inferior rectus – depresses the eyeball
▸ Medial rectus – adducts the eyeball
▸ Inferior oblique – elevates, abducts and laterally rotates the
eyeball
8. OCULOMOTOR NERVE
CN III: MOTOR FUNCTIONS
▸ Superior Branch
▸ Superior rectus – elevates the eyeball
▸ Levator palpabrae superioris – raises the upper eyelid
▸ Additionally, there are sympathetic fibres that travel with the
superior branch of the oculomotor nerve
▸ innervate the superior tarsal muscle
▸ acts to keep the eyelid elevated after the levator palpabrae
superioris has raised it
10. OCULOMOTOR NERVE
CN III: PARASYMPATHETIC FUNCTIONS
▸ There are two structures in the eye that receive parasympathetic innervation
from the oculomotor nerve:
▸ Sphincter pupillae – constricts the pupil, reducing the amount of light
entering the eye
▸ Ciliary muscles – contracts, causes the lens to become more spherical,
and thus more adapted to short range vision
▸ The pre-ganglionic parasympathetic fibres travel in the inferior branch of the
oculomotor nerve
▸ Within the orbit, they branch off and synapse in the ciliary ganglion
▸ The post-ganglionic fibres are carried to the eye via the short ciliary nerves
15. References
▸ These slide reflect a summary of the contents of
TeachMeAnatomy.info and are to be used for
educational purposes only in compliance with the
terms of use policy.
Specific portions referenced in this summary are as
follows:
▸ https://teachmeanatomy.info/head/cranial-nerves/
oculomotor/
▸ Additional sources are referenced on the slide
containing that specific content.
