The Oculomotor Nerve (CN III)
The Oculomotor Nerve (CN III)
- Last updated November 23, 2025
✅ Objectives
By the end of these revision notes, you should be able to:
- Define the anatomy of the oculomotor nerve
- Be aware of the structures supplied by the oculomotor nerve
- Understand how to examine the nerve
The Basics
The oculomotor nerve is the third cranial nerve (CN III). It is a motor nerve with parasympathetic fibres, primarily involved in eye movement and pupillary constriction.
Anatomy of the Oculomotor Nerve
Origin
The oculomotor nerve arises from the oculomotor nucleus (providing motor function) and the Edinger-Westphal nucleus (providing parasympathetic function) in the midbrain.
Course
The nerve exits the midbrain anteriorly and passes between the posterior and superior cerebral arteries.
It then runs through the lateral wall of the cavernous sinus and enters the orbit through the superior orbital fissure.
Divisions in the Orbit
There are two divisions to the nerve:
- Superior division – this supplies the superior rectus and levator palpebrae superioris
- Inferior division – this supplies the medial rectus, inferior rectus, inferior oblique muscles and carries parasympathetic fibres to the ciliary ganglion
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