Anatomy: Oculomotor Nerve

1. OCULOMOTOR NERVE
ANATOMY

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

5. https://teachmeanatomy.info/head/cranial-nerves/oculomotor/

6. https://teachmeanatomy.info/head/cranial-nerves/oculomotor/

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

9. https://teachmeanatomy.info/head/cranial-nerves/oculomotor/

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

11. https://teachmeanatomy.info/head/cranial-nerves/oculomotor/

12. https://teachmeanatomy.info/head/cranial-nerves/oculomotor/

13. https://teachmeanatomy.info/head/cranial-nerves/oculomotor/

14. https://teachmeanatomy.info/head/cranial-nerves/oculomotor/

15. References
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oculomotor/
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