Which cranial nerve is primarily responsible for pure motor function?

The oculomotor nerve is primarily responsible for pure motor function, as it is involved in controlling most of the eye's movements, including the elevation of the eyelid and the constriction of the pupil. Specifically, it innervates four of the six extraocular muscles that facilitate eye movement – the superior rectus, inferior rectus, medial rectus, and inferior oblique muscles. This motor function distinguishes it from other cranial nerves that may have sensory components or mixed functions.

In contrast, the trochlear and abducens nerves, while also primarily motor, are specifically responsible for controlling only one muscle each. The trochlear nerve innervates the superior oblique muscle, and the abducens innervates the lateral rectus muscle. Although they are pure motor nerves, they do not have the broad range of motor control that the oculomotor nerve does.

The trigeminal nerve, on the other hand, is primarily a sensory nerve responsible for sensation in the face, with a smaller branch (the mandibular division) contributing to motor control for muscles of mastication. This mix of sensory and motor functions further differentiates it from the pure motor role of the oculomotor nerve.

Thus, when considering