What cranial nerve is responsible for the afferent limb of the pupillary light reflex?

The cranial nerve that is responsible for the afferent limb of the pupillary light reflex is cranial nerve II, also known as the optic nerve. This nerve carries sensory information from the retina of the eye to the brain. When light is shone into one eye, the optic nerve transmits signals regarding the intensity of the light to the midbrain, specifically to the pretectal nuclei. This process initiates the pupillary light reflex, which involves constriction of the pupil to protect the retina from excessive light.

Cranial nerve II plays a crucial role in this reflex as it is the pathway through which visual information enters the central nervous system. The response of pupil constriction occurs through pathways that include other cranial nerves, but the initial sensory input that triggers the reflex originates from the optic nerve.