Which cranial nerve is responsible for controlling pupil response?

The cranial nerve responsible for controlling pupil response is cranial nerve III, also known as the oculomotor nerve. This nerve plays a critical role in the movement of most extraocular muscles, as well as in the regulation of the size of the pupil. When light is shone into the eye, cranial nerve III mediates the constriction of the pupil through parasympathetic fibers, which is a key part of the pupillary response to light.

Cranial nerve II, known as the optic nerve, is primarily responsible for vision and transmitting visual information from the retina to the brain. While it is involved in the pupillary light reflex by providing sensory input, it does not control the motor response of the pupil.

Cranial nerve IV, the trochlear nerve, and cranial nerve VI, the abducens nerve, are primarily concerned with the movement of specific extraocular muscles (superior oblique and lateral rectus, respectively) but do not have a role in pupil response. Their functions are more related to eye movement rather than pupil constriction or dilation. Thus, cranial nerve III is correctly identified as the nerve that directly influences pupil response.