Suprachiasmatic nucleus

From Wikipedia, the free encyclopedia

Jump to navigationJump to search

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

(皮層是會(huì)投射到lateral geniculate nucleus的，從而通過(guò)visual cortex影響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應(yīng)該是去抑制ventrolateral preoptic area，而興奮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.

（這說(shuō)明rhythmicity現(xiàn)象并不依賴(lài)于SCN，而只有SCN能接收外界視覺(jué)信息來(lái)影響控制rhythmicity的核團(tuán)。除此，還要注意某些個(gè)raphe nucleus也投射到SCN，也就是情緒的好壞會(huì)一定程度左右rhythmicity的變化，但是NE遞質(zhì)似乎并不投射到SCN。那么那些serotonin分泌濃度低下的人是不是存在與正常情況明顯不同的rhythmicity現(xiàn)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.

（進(jìn)入retina光的多與少，涉及交感與副交感，換句話(huà)說(shuō)就是你自身調(diào)節(jié)交感系統(tǒng)和副交感系統(tǒng)活動(dòng)比例時(shí)，順帶著會(huì)影響瞳孔的大小，從而身體主動(dòng)影響進(jìn)入視網(wǎng)膜光的多與少。簡(jiǎn)而言之，情緒的變化會(huì)影響允許進(jìn)入光的多少，進(jìn)的多，意味著信號(hào)強(qiáng)烈，進(jìn)的少，意味著需要通過(guò)其他手段來(lái)補(bǔ)充皮層信號(hào)不足的那些地方，這點(diǎn)體驗(yàn)應(yīng)該是每個(gè)人都能感受到的，可能會(huì)意識(shí)不到。光進(jìn)入的多，就不那么需要通過(guò)其他手段來(lái)補(bǔ)充皮層信號(hào)，也不利于分辨細(xì)節(jié)--可能指的就是銳度，從而能夠更客觀(guān)地記錄視覺(jué)信息，而夜晚光不足，則需要強(qiáng)烈地通過(guò)其他手段來(lái)補(bǔ)充皮層信號(hào)，從而完成事物辨認(rèn)和具體行動(dòng)，也是"各種妖魔鬼怪"在腦中產(chǎn)生的時(shí)候，據(jù)我觀(guān)察，孩子似乎從兩歲半開(kāi)始怕黑。

對(duì)了，反過(guò)來(lái)，光的強(qiáng)弱也能夠明顯地影響交感系統(tǒng)和副交感系統(tǒng)，比如進(jìn)入一個(gè)全白的房間，可能會(huì)一瞬間感覺(jué)心情大好，而進(jìn)入較暗的房間則會(huì)覺(jué)得不舒服，顯然這對(duì)應(yīng)著交感系統(tǒng)的變化，過(guò)多的光強(qiáng)激發(fā)交感系統(tǒng)，然后用serotonin來(lái)平抑交感系統(tǒng)，這個(gè)過(guò)程就對(duì)應(yīng)心情大好；而過(guò)少的光，需要激發(fā)NE系統(tǒng)來(lái)提高丘腦與大腦皮層的NE濃度，降低serotonin的濃度，從而提高神經(jīng)細(xì)胞的敏感度，這對(duì)應(yīng)著相反的情緒體驗(yàn)，或者說(shuō)進(jìn)入相反的情緒狀態(tài)可以提高神經(jīng)細(xì)胞的敏感度。我發(fā)現(xiàn)關(guān)于瞳孔的大小與自主神經(jīng)系統(tǒng)、彌散性調(diào)節(jié)系統(tǒng)、大腦皮層可以寫(xiě)出很多分析內(nèi)容，而眼球的轉(zhuǎn)動(dòng)則與黑質(zhì)、上丘、大腦皮層、腦橋的膽堿能核團(tuán)、VTA有很密切關(guān)系，換句話(huà)說(shuō)，就是通過(guò)觀(guān)察眼睛就可以獲得上述這些結(jié)構(gòu)的活動(dòng)信息，不過(guò)就先寫(xiě)這些吧。）