Neuroanatomy, Edinger–Westphal Nucleus (Accessory Oculomotor Nucleus)

The Edinger-Westphal (EW) nucleus, which is part of the oculomotor nuclear complex (ONC), was first described in the literature in the 17th century (see Edinger-Westphal Nucleus). Recently, it has been discovered that 2 different cell populations within the EW nucleus– subdivide into the EW preganglionic (EWpg) population and the EW nucleus centrally projecting (EWcp) population. However, the accepted nomenclature for these 2 groups varies. The EWpg is what is thought of as the classic ONC—sending parasympathetic nerve fibers toward the eye. It is located in the midbrain immediately dorsal to the oculomotor nucleus near the level of the superior colliculus, which is why it is often included in the overarching term oculomotor complex (see Midbrain Anatomy). The EWcp population of cells (the non-preganglionic EW cells), also referred to as the subgriseal paramedian midbrain neuronal stream to reflect their actual path, differ in function from the EWpg nucleus. However, the name subgriseal paramedian midbrain neuronal stream has not been found favorable in the literature due to the complexity of the name and the belief that the EW nucleus consisted of only 1 cell type. These 2 bodies of cells, referred to as the EW nucleus and intermingled from a structural standpoint in the midbrain, have fundamentally different roles in function.