edingerwestphal

The Edinger–Westphal nucleus is a parasympathetic nucleus located in the dorsal midbrain, part of the oculomotor (cranial nerve III) complex. It lies near the oculomotor nucleus in the tegmentum, surrounding the periaqueductal gray at the level of the superior colliculus.

The neurons of this nucleus are preganglionic parasympathetic cells whose axons travel with the inferior division of CN III to the ciliary ganglion. Postganglionic fibers from the ciliary ganglion innervate the sphincter pupillae and the ciliary muscle. This pathway enables pupillary constriction and accommodation for near vision. The Edinger–Westphal nucleus receives input from the pretectal area and participates in the pupillary light reflex as part of the reflex arc.

Clinical significance arises from disruption of this parasympathetic outflow. Lesions can produce a dilated pupil (mydriasis) and impaired accommodation in the affected eye, with reduced or absent pupillary light reflex. In dorsal midbrain (Parinaud) syndrome, lesions impacting this region can also cause vertical gaze palsies and light–near dissociation, reflecting involvement of the midbrain circuits that coordinate eye movements and reflexes.

History and nomenclature note that the nucleus is named for Karl E. Edinger and Friedrich Westphal, who described its parasympathetic role in the late 19th century. In contemporary texts, it is recognized as the brainstem source of preganglionic parasympathetic neurons that control pupillary constriction and accommodation via the ciliary ganglion.