Editing Suprachiasmatic nucleus (section)

==Electrophysiology==
Neurons in the SCN fire [[action potential]]s in a 24-hour rhythm, even under constant conditions.<ref name=":0">{{Cite journal |last1=Welsh |first1=David K. |last2=Takahashi |first2=Joseph S. |last3=Kay |first3=Steve A. |date=2010-03-17 |title=Suprachiasmatic Nucleus: Cell Autonomy and Network Properties |journal=Annual Review of Physiology |language=en |volume=72 |issue=1 |pages=551–577 |doi=10.1146/annurev-physiol-021909-135919 |issn=0066-4278 |pmc=3758475 |pmid=20148688}}</ref> At mid-day, the firing rate reaches a maximum, and, during the night, it falls again. Rhythmic expression of circadian regulatory genes in the SCN requires depolarization in the SCN neurons via [[Calcium in biology|calcium]] and [[Cyclic adenosine monophosphate|cAMP]].<ref name=":0" />  Thus, depolarization of SCN neurons via cAMP and calcium contributes to the magnitude of the rhythmic gene expression in the SCN.<ref name=":0" />

Further, the SCN synchronizes nerve impulses which spread to various [[Parasympathetic nervous system|parasympathetic]] and [[Sympathetic nervous system|sympathetic]] nuclei.<ref name=":1">{{Cite journal |last=Okamura |first=H. |date=2007 |title=Suprachiasmatic Nucleus Clock Time in the Mammalian Circadian System |journal=Cold Spring Harbor Symposia on Quantitative Biology |language=en |volume=72 |issue=1 |pages=551–556 |doi=10.1101/sqb.2007.72.033 |pmid=18419314 |issn=0091-7451|doi-access=free }}</ref> The sympathetic nuclei drive [[glucocorticoid]] output from the [[adrenal gland]] which activates [[PER1|Per1]] in the body cells, thus resetting the circadian cycle of cells in the body.<ref name=":1" /> Without the SCN, rhythms in body cells dampen over time, which may be due to lack of synchrony between cells.<ref name=":0" />

Many SCN neurons are sensitive to light stimulation via the retina.<ref>{{Cite journal |last1=Morin |first1=L.P. |last2=Allen |first2=C.N. |date=2006 |title=The circadian visual system, 2005 |url=https://linkinghub.elsevier.com/retrieve/pii/S0165017305001165 |journal=Brain Research Reviews |language=en |volume=51 |issue=1 |pages=1–60 |doi=10.1016/j.brainresrev.2005.08.003|pmid=16337005 |s2cid=41579061 |url-access=subscription }}</ref> The photic response is likely linked to effects of light on circadian rhythms. In addition, application of melatonin in live rats and isolated SCN cells can decrease the firing rate of these neurons.<ref>{{Cite journal |last1=van den Top |first1=M |last2=Buijs |first2=R.M |last3=Ruijter |first3=J.M |last4=Delagrange |first4=P |last5=Spanswick |first5=D |last6=Hermes |first6=M.L.H.J |date=2001 |title=Melatonin generates an outward potassium current in rat suprachiasmatic nucleus neurones in vitro independent of their circadian rhythm |url=https://linkinghub.elsevier.com/retrieve/pii/S0306452201003463 |journal=[[Neuroscience (journal)|Neuroscience]] |language=en |volume=107 |issue=1 |pages=99–108 |doi=10.1016/S0306-4522(01)00346-3|pmid=11744250 |s2cid=12064196 |url-access=subscription }}</ref><ref>{{Cite journal |last1=Yang |first1=Jing |last2=Jin |first2=Hui Juan |last3=Mocaër |first3=Elisabeth |last4=Seguin |first4=Laure |last5=Zhao |first5=Hua |last6=Rusak |first6=Benjamin |date=2016-06-15 |title=Agomelatine affects rat suprachiasmatic nucleus neurons via melatonin and serotonin receptors |url=https://www.sciencedirect.com/science/article/pii/S0024320516302557 |journal=Life Sciences |language=en |volume=155 |pages=147–154 |doi=10.1016/j.lfs.2016.04.035 |pmid=27269050 |issn=0024-3205|url-access=subscription }}</ref> Variances in light input due to [[jet lag]], seasonal changes, and constant light conditions all change the firing rhythm in SCN neurons demonstrating the relationship between light and SCN neuronal functioning.<ref name=":0" />