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

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.