![]() ![]() These blood vessels are part of the vertebrobasilar circulation and include the basilar artery, superior cerebellar artery, and posterior cerebral artery. While there is not a single blood supply to the EW nucleus, it receives its blood supply via vessels that feed the midbrain and brainstem. Post-mortem studies in neonates who suffered prenatal hypoxia have shown there to be an expression of urocortin-1 from the EWcp as early as 34 weeks gestation-demonstrating both the development of the EW nucleus at this age and specifically the EWcp role in stress response. As part of the midbrain, the EW nucleus develops with the midbrain arc, which is under the control of the homeobox genes Sonic Hedgehog and FGF8. The thought is that brain nuclei develop as part of neuromeres and arcs (distinct columns of cells in the brain with high levels of acetylcholinesterase). Nucleogenesis in the brain during embryologic development is a subject of ongoing research. However, it is thought that the response to stress by the EWcp nucleus is separate from that of the hypothalamic-pituitary-adrenal (HPA) axis. Studies have shown that this nucleus is involved in stress adaptation, anxiety, and pain. The EWcp nucleus significantly contributes to the amount of urocortin-1 neuropeptide in the brain. These differ immunohistochemically from the cholinergic parasympathetic neurons of the EWpg, which are choline acetyltransferase positive. It is known that a large population of these cells are urocortinergic neurons, which are positive for the neuropeptide urocortin-1 (part of the corticotropin-releasing factor family) and negative for choline acetyltransferase. The EWcp is located medial and dorsal to the OCN in the midbrain and is comprised of a collection of peptidergic neuron cell bodies. ![]() Since the discovery of the two cell populations of the EW nucleus, the function of the EWcp has been a subject of ongoing research. Additionally, the contraction of the ciliary muscles leads to the relaxation of the zonular fibers, allowing for increased convexity of the lens and, subsequently, an increase in refractive power and accommodation. The constriction of the pupil moderates the amount of light the retina is exposed to, which is the efferent limb of the pupillary light reflex. This relay leads to the innervation of the sphincter pupillae (causing miosis) and ciliary muscles (ocular accommodation). In response to the signal from the EWpg, the postganglionic ciliary bodies relay the signal along their axons by way of the ciliary nerves towards the eye. This synapse between the EWpg nerve fibers and the ciliary ganglion postganglionic cell bodies is a nicotinic synapse with acetylcholine as the neurotransmitter. The EWpg nucleus receives input from the locus ceruleus in response to the light hitting the retina, which then prompts the nucleus to send a forward signal that synapses at the postganglionic cells of the ciliary ganglion (CG). These cell bodies participate in the light reflex pathway that leads to pupillary constriction when the retina has exposure to light. The EWpg nucleus is comprised of preganglionic cell bodies that track along the course of the oculomotor nerve (cranial nerve III) toward the postganglionic ciliary bodies. The EWpg nucleus houses choline acetyltransferase-positive cell bodies responsible for the parasympathetic innervation of the eye. These two bodies of cells, while both referred to as the EW nucleus and intermingled from a structural standpoint in the midbrain, have fundamentally different roles in function. However, the name subgriseal paramedian midbrain neuronal stream has not found favor in the literature due to the complexity of the name and the belief that the EW nucleus consisted of only one cell type. 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. 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. The EWpg is what is thought of as the classic ONC-sending parasympathetic nerve fibers toward the eye. However, the accepted nomenclature for these two groups varies. Recently, it has been discovered that two different cell populations within the EW nucleus – and, in fact, it subdivides into the EW preganglionic (EWpg) population and the EW nucleus centrally projecting (EWcp) population. The Edinger-Westphal (EW) nucleus, which is part of the oculomotor nuclear complex (ONC), was first described in the literature in the 17th century. ![]()
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