Lower Motor Apparatus Practice Test 2026 – Full Exam Prep Guide

Pupil constriction is driven by parasympathetic signals that originate in the Edinger-Westphal nucleus. These preganglionic neurons ride the oculomotor nerve to the ciliary ganglion, where they synapse and send postganglionic fibers to the sphincter pupillae muscle. When this pathway is activated, the pupil constricts in response to light or during focusing on close objects (accommodation).

The other nuclei listed have different autonomic or motor roles: the dorsal motor nucleus supplies parasympathetic outflow to thoracic and abdominal organs; the salivatory nuclei control parasympathetic input to the salivary glands (and lacrimal flow via interconnected pathways); the trochlear nucleus provides somatic motor to the superior oblique muscle. The Edinger-Westphal nucleus is specifically tied to the parasympathetic control of the pupil through the oculomotor pathway.