Editing Suprachiasmatic nucleus (section)

==Neuroanatomy==
The SCN is situated in the [[anterior]] part of the hypothalamus immediately [[Anatomical terms of location#Dorsal and ventral|dorsal]], or ''superior'' (hence [[Supra (grammar)|supra]]) to the [[optic chiasm]] bilateral to (on either side of) the [[third ventricle]]. It consists of two nuclei composed of approximately 10,000 neurons.<ref name=":2"/>

The [[Morphology (biology)|morphology]] of the SCN is species dependent.<ref name=lpm>{{Cite journal |last=Morin |first=Lawrence P. |date=May 2013 |title=Neuroanatomy of the extended circadian rhythm system |journal=Experimental Neurology |volume=243 |pages=4–20 |doi=10.1016/j.expneurol.2012.06.026 |issn=1090-2430 |pmc=3498572 |pmid=22766204}}</ref> Distribution of different cell phenotypes across specific SCN regions, such as the concentration of VP-IR neurons, can cause the shape of the SCN to change.<ref name=lpm />

The nucleus can be divided into [[ventrolateral]] and [[dorsolateral]] portions, also known as the core and shell, respectively.<ref name=":2">{{Citation |last1=Ma |first1=Melinda A. |title=Neuroanatomy, Nucleus Suprachiasmatic |date=2023 |url=http://www.ncbi.nlm.nih.gov/books/NBK546664/ |work=StatPearls |access-date=2023-04-09 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=31536270 |last2=Morrison |first2=Elizabeth H.}}</ref> These regions differ in their expression of the clock genes, the core expresses them in response to stimuli whereas the shell expresses them constitutively.

In terms of projections, the core receives innervation via three main pathways, the [[retinohypothalamic tract]], geniculohypothalamic tract, and projections from some [[raphe nuclei]].<ref name=lpm /> The dorsomedial SCN is mainly innervated by the core and also by other hypothalamic areas. Lastly, its output is mainly to the subparaventricular zone and [[dorsomedial hypothalamic nucleus]] which both mediate the influence SCN exerts over circadian regulation of the body.<ref name=lpm />

The most abundant peptides found within the SCN are [[arginine-vasopressin]] (AVP), [[Vasoactive intestinal peptide|vasoactive intestinal polypeptide]] (VIP), and [[Peptide histidine isoleucine|peptide histidine-isoleucine]] (PHI). Each of these peptides are localized in different regions. Neurons with AVP are found dorsomedially, whereas VIP-containing and PHI-containing neurons are found ventrolaterally.<ref>{{Cite journal |last=Reuss |first=Stefan |date=1996-08-01 |title=Components and connections of the circadian timing system in mammals |url=https://doi.org/10.1007/s004410050652 |journal=Cell and Tissue Research |language=en |volume=285 |issue=3 |pages=353–378 |doi=10.1007/s004410050652 |pmid=8772150 |s2cid=17338595 |issn=1432-0878|url-access=subscription }}</ref>