What is the effect of parasympathetic control on the pupil?

• A. It constricts the pupil (miosis).
• B. It dilates the pupil (mydriasis).
• C. It increases tear production.
• D. It changes lens curvature.

Answer: (A)

Parasympathetic control tightens the pupil by contracting the sphincter pupillae muscle. The signal travels from the brainstem (Edinger–Westphal nucleus) through the oculomotor nerve to the ciliary ganglion, then via short ciliary nerves to the sphincter pupillae. Acetylcholine released at these muscarinic receptors causes the muscle to constrict, reducing the pupil diameter (miosis). This is the opposite of sympathetic activity, which dilates the pupil by activating the dilator pupillae.

In addition to affecting pupil size, parasympathetic activity can increase tear production and stimulate the ciliary muscle to change lens shape for near vision, but the question specifically asks about the pupil, where constriction is the primary effect.