Which cranial nerve is primarily responsible for pupil constriction?

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Study for the History and Physical (Handamp;P) Exam 1. Prepare with flashcards and multiple choice questions, each question has hints and explanations. Get ready for your exam!

Multiple Choice

Which cranial nerve is primarily responsible for pupil constriction?

Explanation:
Parasympathetic input to the iris via the oculomotor nerve is what drives pupil constriction. The preganglionic fibers come from the Edinger-Westphal nucleus, travel with CN III to the ciliary ganglion, then postganglionic fibers ride with the short ciliary nerves to the sphincter pupillae, causing the pupil to constrict in bright light or during near focus. The other nerves shown are involved in eye movement or facial sensation and do not govern the sphincter pupillae. (Sympathetic pathways dilate the pupil, not constrict it.)

Parasympathetic input to the iris via the oculomotor nerve is what drives pupil constriction. The preganglionic fibers come from the Edinger-Westphal nucleus, travel with CN III to the ciliary ganglion, then postganglionic fibers ride with the short ciliary nerves to the sphincter pupillae, causing the pupil to constrict in bright light or during near focus. The other nerves shown are involved in eye movement or facial sensation and do not govern the sphincter pupillae. (Sympathetic pathways dilate the pupil, not constrict it.)

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