wiki笔记--Suprachiasmatic nucleus--2021/11/27
Suprachiasmatic nucleus
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Suprachiasmatic nucleus
Suprachiasmatic nucleus is SC, at center left, labelled in blue.
The optic chiasm is OC, just below, labelled in black.
Suprachiasmatic nucleus is labelled and shown in green.
Details
Identifiers
Latin
nucleus suprachiasmaticus
MeSH
D013493
NeuroNames
384
NeuroLex ID
birnlex_1325
TA98
A14.1.08.911
TA2
5720
FMA
67883
Anatomical terms of neuroanatomy
[edit on Wikidata]
The suprachiasmatic nucleus or nuclei (SCN) is a tiny region of the brain in the hypothalamus, situated directly above the optic chiasm. It is responsible for controlling circadian rhythms. The neuronal and hormonal activities it generates regulate many different body functions in a 24-hour cycle. The mouse SCN contains approximately 20,000 neurons.[1]
The SCN interacts with many other regions of the brain. It contains several cell types and several different peptides (including vasopressin and vasoactive intestinal peptide) and neurotransmitters.
Contents
· 1Neuroanatomy
· 2Circadian effects
· 3Circadian rhythms of endothermic (warm-blooded) and ectothermic (cold-blooded) vertebrates
· 3.1The SCN of endotherms and ectotherms
· 3.2Behaviors controlled by the SCN of vertebrates
· 4Other signals from the retina
· 5Gene expression
· 5.1Fruitfly
· 5.2Mammals
· 6Electrophysiology
· 7See also
· 8References
· 9External links
Neuroanatomy[edit]
The SCN is situated in the anterior part of the hypothalamus immediately dorsal, or superior (hence supra) to the optic chiasm (CHO) bilateral to (on either side of) the third ventricle.
The nucleus can be divided into ventrolateral and dorsolateral portions, also known as the core and shell, respectively. 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
(皮层是会投射到lateral geniculate nucleus的，从而通过visual cortex影响SCN。)
, and projections from some Raphe nuclei. 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.
（The DMH sends information to the ventrolateral preoptic area, locus coeruleus, and orexinergic neurons in order to aid in the regulation of wakefulness. 那么， dorsomedial hypothalamic nucleus应该是去抑制ventrolateral preoptic area，而兴奋locus coeruleus and orexinergic neurons。The dorsomedial hypothalamic nucleus (DMH) receives its circadian information from the suprachiasmatic nucleus, both directly and via subparaventricular zone, and senses leptin and other feeding cues。）
Circadian effects[edit]
Different organisms such as bacteria,[2] plants, fungi, and animals, show genetically based near-24-hour rhythms. Although all of these clocks appear to be based on a similar type of genetic feedback loop, the specific genes involved are thought to have evolved independently in each kingdom. Many aspects of mammalian behavior and physiology show circadian rhythmicity, including sleep, physical activity, alertness, hormone levels, body temperature, immune function, and digestive activity. The SCN coordinates these rhythms across the entire body, and rhythmicity is lost if the SCN is destroyed. For example, total time of sleep is maintained in rats with SCN damage, but the length and timing of sleep episodes becomes erratic.
（这说明rhythmicity现象并不依赖于SCN，而只有SCN能接收外界视觉信息来影响控制rhythmicity的核团。除此，还要注意某些个raphe nucleus也投射到SCN，也就是情绪的好坏会一定程度左右rhythmicity的变化，但是NE递质似乎并不投射到SCN。那么那些serotonin分泌浓度低下的人是不是存在与正常情况明显不同的rhythmicity现象。我就想知道是哪些raphe nucleus投射到SCN。）
The SCN maintains control across the body by synchronizing "slave oscillators," which exhibit their own near-24-hour rhythms and control circadian phenomena in local tissue.[3]
The SCN receives input from specialized photosensitive ganglion cells in the retina via the retinohypothalamic tract. Neurons in the ventrolateral SCN (vlSCN) have the ability for light-induced gene expression. Melanopsin-containing ganglion cells in the retina have a direct connection to the ventrolateral SCN via the retinohypothalamic tract. When the retina receives light, the vlSCN relays this information throughout the SCN allowing entrainment, synchronization, of the person's or animal's daily rhythms to the 24-hour cycle in nature. The importance of entraining organisms, including humans, to exogenous cues such as the light/dark cycle, is reflected by several circadian rhythm sleep disorders, where this process does not function normally.[4]
Neurons in the dorsomedial SCN (dmSCN) are believed to have an endogenous 24-hour rhythm that can persist under constant darkness (in humans averaging about 24 hours 11 min).[5] A GABAergic mechanism is involved in the coupling of the ventral and dorsal regions of the SCN.[6]
The SCN sends information to other hypothalamic nuclei and the pineal gland to modulate body temperature and production of hormones such as cortisol and melatonin.[citation needed]
Other signals from the retina[edit]
A variation of an eskinogram showing the influence of light and darkness on circadian rhythms and related physiology and behavior through the SCN in humans
The SCN is one of many nuclei that receive nerve signals directly from the retina.
Some of the others are the lateral geniculate nucleus (LGN), the superior colliculus, the basal optic system, and the pretectum:
· The LGN passes information about color, contrast, shape, and movement on to the visual cortex and itself signals to the SCN.
· The superior colliculus controls the movement and orientation of the eye.
· The basal optic system also controls eye movements.[12]
The pretectum controls the size of the pupil.
（进入retina光的多与少，涉及交感与副交感，换句话说就是你自身调节交感系统和副交感系统活动比例时，顺带着会影响瞳孔的大小，从而身体主动影响进入视网膜光的多与少。简而言之，情绪的变化会影响允许进入光的多少，进的多，意味着信号强烈，进的少，意味着需要通过其他手段来补充皮层信号不足的那些地方，这点体验应该是每个人都能感受到的，可能会意识不到。光进入的多，就不那么需要通过其他手段来补充皮层信号，也不利于分辨细节--可能指的就是锐度，从而能够更客观地记录视觉信息，而夜晚光不足，则需要强烈地通过其他手段来补充皮层信号，从而完成事物辨认和具体行动，也是"各种妖魔鬼怪"在脑中产生的时候，据我观察，孩子似乎从两岁半开始怕黑。
对了，反过来，光的强弱也能够明显地影响交感系统和副交感系统，比如进入一个全白的房间，可能会一瞬间感觉心情大好，而进入较暗的房间则会觉得不舒服，显然这对应着交感系统的变化，过多的光强激发交感系统，然后用serotonin来平抑交感系统，这个过程就对应心情大好；而过少的光，需要激发NE系统来提高丘脑与大脑皮层的NE浓度，降低serotonin的浓度，从而提高神经细胞的敏感度，这对应着相反的情绪体验，或者说进入相反的情绪状态可以提高神经细胞的敏感度。我发现关于瞳孔的大小与自主神经系统、弥散性调节系统、大脑皮层可以写出很多分析内容，而眼球的转动则与黑质、上丘、大脑皮层、脑桥的胆碱能核团、VTA有很密切关系，换句话说，就是通过观察眼睛就可以获得上述这些结构的活动信息，不过就先写这些吧。）
