Preganglionic parasympathetic fibers begin at which nucleus?

• A. Edinger Westphal nucleus
• B. Superior Salivatory nucleus
• C. Dorsal motor nucleus of Vagus
• D. Nucleus ambiguus

Answer: (A)

The fibers you're looking for come from a midbrain parasympathetic nucleus that specifically serves the eye. The Edinger–Westphal nucleus houses the preganglionic parasympathetic neurons that project with the oculomotor nerve to the ciliary ganglion. From there, postganglionic fibers pass via short ciliary nerves to the sphincter pupillae and ciliary muscle, producing pupil constriction and accommodation.

The other nuclei have different roles: the Superior Salivatory nucleus provides preganglionic parasympathetic fibers to lacrimal and some salivary glands via the facial nerve; the Dorsal motor nucleus of the Vagus supplies parasympathetic innervation to thoracic and most abdominal viscera; the Nucleus ambiguus mainly contains motor neurons for the pharynx and larynx, with autonomic contributions not tied to the ocular parasympathetic outflow. Thus, the Edinger–Westphal nucleus is the source of preganglionic parasympathetic fibers to the eye.