Loss of pupillary constriction is a sign of damage to which cranial nerve?

Loss of pupillary constriction is primarily associated with damage to cranial nerve III, also known as the oculomotor nerve. This nerve is responsible for controlling most of the eye's movements, as well as the constriction of the pupil. The parasympathetic fibers carried by the oculomotor nerve originate in the brainstem and facilitate the constriction of the pupil in response to light or accommodation. When this nerve is damaged, the normal response to light is compromised, resulting in a dilated pupil that does not constrict appropriately.

Cranial nerve I is responsible for the sense of smell and is not involved in pupillary constriction. Cranial nerve II is primarily concerned with visual input and does not directly control the muscles involved in pupil constriction. Cranial nerve IV, the trochlear nerve, is involved in innervating the superior oblique muscle of the eye and does not play a role in pupillary constriction. Thus, the damage associated with loss of pupillary constriction is clearly linked to cranial nerve III.