Which nerve is primarily responsible for the constriction of the pupil?

The oculomotor nerve is primarily responsible for the constriction of the pupil due to its role in the parasympathetic innervation of the eye. It carries parasympathetic fibers that originate in the Edinger-Westphal nucleus and synapse in the ciliary ganglion. From there, the postganglionic fibers innervate the sphincter pupillae muscle, which controls the constriction of the pupil. This process, known as miosis, is crucial for regulating the amount of light entering the eye and enhancing visual acuity in bright conditions.

In contrast, the other nerves listed do not play a direct role in pupil constriction. The trigeminal nerve is primarily responsible for sensation in the face and motor functions for chewing, while the facial nerve controls muscles of facial expression and carries taste sensations. The hypoglossal nerve is involved in the motor control of the tongue muscles. Therefore, understanding the specific functions of these nerves highlights why the oculomotor nerve is the correct choice for pupil constriction.