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Anatomy of the oculomotor (CN III), trochlear (CN IV) and abducens (CN VI) nerves

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Notes

Figure 1: Somatic motor innervation of the oculomotor nerve (CN III).
Figure 2: Schematic of the pupillary light reflex.
Figure 3: Schematic of the accommodation reflex.
Figure 4: Anatomy of the trochlear nerve (CN IV).
Figure 5: Anatomy of the abducens nerve (CN VI).
Nerve
Fiber type(s)
Location of cell bodies
Exit from cranium
Function(s)
Oculomotor (CN III)
Somatic motor
Midbrain (Oculomotor nucleus)





Superior orbital fissure
Motor to superior, inferior,
and medial recti, inferior oblique, and levator palpebrae superioris muscles.
Visceral motor
Presynaptic: Midbrain (Edinger–Westphal nucleus)
Postsynaptic: Ciliary ganglion
Parasympathetic innervation to sphincter pupillae (constricts pupil) and ciliary muscles (accommodation of lens)
Trochlear (CN IV)
Somatic motor
Midbrain (Trochlear nucleus)
Motor to superior oblique muscle, which abducts, depresses, and medially rotates eye
Abducens (CN VI)
Somatic motor
Pons (Abducens nucleus)
Motor to lateral rectus muscle which abducts the eye

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Content Reviewers

Viviana Popa, MD,Scott Caterine, BSc (Hons.), MSc, MB, BCh, BAO (Hons.)

Imagine a world where we had no control over the movements of our eyes.

We would have to move our entire head in that direction to look at something new, something that would surely cause neck issues when playing video games.

Luckily, we do have control over our eye movements, and the cranial nerves which innervate the extrinsic ocular muscles that move the eyeball are the oculomotor, trochlear, and abducens nerve - or cranial nerves III, IV and VI.

First up, the oculomotor nerve has two main motor functions: a somatic motor function and a visceral motor or parasympathetic function, and there are different motor nuclei that control these two functions.

So, the somatic motor function is controlled by the oculomotor nucleus which is located in the midbrain, and the visceral motor function is controlled by the accessory oculomotor nucleus, or Edinger-Westphal nucleus, also located in the midbrain.

The oculomotor nerve innervates four of the six extraocular muscles, namely the superior rectus, medial rectus, inferior rectus and inferior oblique muscle.

Thanks to this cranial nerve, it mainly helps us to direct our gaze superiorly, inferiorly, and medially.

The oculomotor nerve also innervates the levator palpebrae superioris muscle, which lifts the superior eyelid.

Parasympathetic innervation is provided through the ciliary ganglion to the smooth muscle of the sphincter pupillae, which causes constriction of the pupil, and to the ciliary body which produces accommodation for near vision by relaxing the lens and allowing it become more rounded.