Which ganglion houses the postganglionic parasympathetic neurons that constrict the pupil?

• A. Ciliary ganglion
• B. Superior cervical ganglion
• C. Pterygopalatine ganglion
• D. Otic ganglion

Answer: (A)

Pupil constriction is driven by the parasympathetic system. The oculomotor nerve carries preganglionic parasympathetic fibers that reach a small relay ganglion in the orbit—the ciliary ganglion. There, they synapse and send postganglionic fibers through the short ciliary nerves to the sphincter pupillae, causing the pupil to constrict. The ciliary ganglion is the site where these postganglionic parasympathetic neurons reside.

The other ganglia serve different autonomic targets: the superior cervical ganglion contains postganglionic sympathetic neurons that dilate the pupil; the pterygopalatine ganglion provides parasympathetic input to lacrimal glands and nasal mucosa; the otic ganglion innervates the parotid gland.