Edinger-Westphal nucleus

The Edinger-Westphal nucleus is the accessory parasympathetic cranial nerve nucleus of the oculomotor nerve (cranial nerve III), supplying the constricting muscles of the iris. Alternatively, the Edinger-Westphal nucleus is a term often used to refer to the adjacent population of non-preganglionic neurons that do not project to the ciliary ganglion, but rather project to the spinal cord, dorsal raphe nucleus, and lateral septal nuclei.

Unlike the classical preganglionic Edinger-Westphal neurons that contain choline acetyltransferase, neurons of the non-preganglionic Edinger-Westphal nucleus contain various  neuropeptides, such as Urocortin and cocaine- and amphetamine-regulated transcript.

Previously, it had been proposed to rename this group of non-preganglionic, neuropeptide-containing neurons to perioculomotor subgriseal neuronal stream, abbreviated pIIISG.

However, more recently, a final nomenclature has been determined. Preganglionic oculomotor neurons within the Edinger-Westphal nucleus shall be referred to as the EWpg, and the neuropeptide-containing neurons shall be known as the centrally-projecting Edinger Westphal nucleus, or EWcp.

Location
The paired nuclei are posterior to the main motor nucleus (oculomotor nucleus) and anterolateral to the cerebral aqueduct in the rostral midbrain at the level of the superior colliculus.

It is the most rostral of the parasympathetic nuclei in the brain stem.

Function
The Edinger-Westphal nucleus supplies preganglionic parasympathetic fibers to the eye, constricting the pupil, accommodating the lens, and convergence of the eyes.

It has also been implicated in the mirroring of pupil size in sad facial expressions. When seeing a sad face, participants' pupils dilated or constricted to mirror the face they saw, which predicted both how sad they perceived the face to be, as well as activity within this region.

Eponym
The nucleus is named for both Ludwig Edinger, from Frankfurt, who demonstrated it in the fetus in 1885, and for Karl Friedrich Otto Westphal, from Berlin, who demonstrated it in the adult in 1887.