EdingerWestphalnukleus

The Edinger-Westphal nucleus is a small parasympathetic nucleus located in the rostral midbrain, forming part of the oculomotor (cranial nerve III) nuclear complex. It contains preganglionic parasympathetic neurons whose axons travel with the oculomotor nerve to the ciliary ganglion.

From the ciliary ganglion, postganglionic fibers innervate the sphincter pupillae, which constricts the pupil, and the ciliary muscle, which adjusts the lens for near vision. Thus the Edinger-Westphal nucleus is essential for pupil constriction and accommodation. The nucleus receives afferent input related to the pupillary light reflex from the retina via the pretectal area and contributes to the efferent limb of this reflex.

Anatomically, the Edinger-Westphal nucleus lies in the rostral midbrain, adjacent to the main oculomotor nucleus. It is typically described as the preganglionic parasympathetic division of the oculomotor complex.

Clinical relevance includes its role in pupillary disorders. Lesions affecting the Edinger-Westphal nucleus or the preganglionic parasympathetic fibers can cause ipsilateral pupil dilation and loss of direct and consensual light reflex, while extraocular movements may be relatively spared. In conditions such as compression of the oculomotor nerve by a posterior communicating artery aneurysm, parasympathetic fibers are often affected first, producing a dilated pupil.

Terminology notes: the structure is historically named after Karl Edinger and Karl Westphal. In modern neuroanatomy it is described as the preganglionic parasympathetic nucleus of the oculomotor complex.