EdingerWestphalKernbahn

The Edinger–Westphal nucleus is a midbrain structure that contains the parasympathetic preganglionic neurons of the oculomotor nerve (cranial nerve III). It is located in the rostral midbrain, near the aqueduct and adjacent to the oculomotor nucleus. Historically described as a single nucleus, contemporary anatomy often distinguishes a preganglionic parasympathetic population, EWpg, responsible for pupillary and lens functions, from a nearby population, EWcp, that has non-ocular roles.

The primary function of the Edinger–Westphal nucleus is to provide preganglionic parasympathetic innervation to the ciliary ganglion. Postganglionic neurons from the ciliary ganglion innervate the sphincter pupillae, which constricts the pupil, and the ciliary muscle, which adjusts the lens for near vision. This pathway is a key component of both the pupillary light reflex and accommodation. Afferent signals from retinal light receptors reach the pretectal area and then influence EW activity to produce pupil constriction in bright light. The same parasympathetic pathway also mediates accommodation by contracting the ciliary muscle.

Clinical relevance includes impaired pupillary constriction and accommodation following damage to the nucleus or its connections, leading to a dilated pupil and reduced light reflex on the affected side. Variants in the organization, such as the EWcp subdivision, reflect additional non-ocular roles identified in modern research.

The Edinger–Westphal nucleus is named after Ludolf Edinger and Karl Westphal, who described midbrain parasympathetic components in the late 19th and early 20th centuries.