Suprachiasmatic nucleus

suprachiasmatic nucleiSCNsuprachiasmatic nucleus (SCN)superchiasmatic nucleus
The suprachiasmatic nucleus or nuclei (SCN) is a tiny region of the brain in the hypothalamus, situated directly above the optic chiasm.wikipedia
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Hypothalamus

hypothalamicanterior hypothalamushypothalamic hormones
The suprachiasmatic nucleus or nuclei (SCN) is a tiny region of the brain in the hypothalamus, situated directly above the optic chiasm.

Vasoactive intestinal peptide

VIPvasoactive intestinal polypeptideVasoactive intestinal peptide (VIP)
It contains several cell types and several different peptides (including vasopressin and vasoactive intestinal peptide) and neurotransmitters.
VIP is produced in many tissues of vertebrates including the gut, pancreas, and suprachiasmatic nuclei of the hypothalamus in the brain.

Vasopressin

antidiuretic hormoneADHarginine vasopressin
It contains several cell types and several different peptides (including vasopressin and vasoactive intestinal peptide) and neurotransmitters.

Melanopsin

OPN4 melanopsin (Opn4)Opsin 4, Melanopsin
Melanopsin-containing ganglion cells in the retina have a direct connection to the ventrolateral SCN via the retinohypothalamic tract.
ipRGCs are photoreceptor cells which are particularly sensitive to the absorption of short-wavelength (blue) visible light and communicate information directly to the area of the brain called the suprachiasmatic nucleus (SCN), also known as the central "body clock", in mammals.

Circadian rhythm sleep disorder

Circadian rhythm sleep disorderscircadian rhythm disordercircadian rhythm disorders
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.
This internal time-keeping mechanism is centralized in the suprachiasmatic nucleus (SCN) of humans and allows for the internal physiological mechanisms underlying sleep and alertness to become synchronized to external environmental cues, like the light-dark cycle.

Circadian rhythm

circadian rhythmscircadiansleep-wake cycle
It is responsible for controlling circadian rhythms.
The primary circadian clock in mammals is located in the suprachiasmatic nucleus (or nuclei) (SCN), a pair of distinct groups of cells located in the hypothalamus.

Retina

retinal diseasesretinalretinal disease
Melanopsin-containing ganglion cells in the retina have a direct connection to the ventrolateral SCN via the retinohypothalamic tract.
It also projects to the superior colliculus, the suprachiasmatic nucleus, and the nucleus of the optic tract.

Intrinsically photosensitive retinal ganglion cells

photosensitive ganglion cellipRGCsintrinsically photosensitive retinal ganglion cells (ipRGCs)
The SCN receives input from specialized photosensitive ganglion cells in the retina via the retinohypothalamic tract.
Previously only projections to the midbrain (pre-tectal nucleus) and hypothalamus (supra-chiasmatic nuclei, SCN) had been shown.

Retinohypothalamic tract

retinohypothalamic
The SCN receives input from specialized photosensitive ganglion cells in the retina via the retinohypothalamic tract. The SCN is known to be involved not only in photoreception through innervation from the retinohypothalamic tract but also in thermoregulation of vertebrates capable of homeothermy, as well as regulating locomotion and other behavioral outputs of the circadian clock within ectothermic vertebrates.
The axons of the ipRGCs belonging to the retinohypothalamic tract project directly, monosynaptically, to the suprachiasmatic nuclei (SCN) via the optic nerve and the optic chiasm.

Entrainment (chronobiology)

entrainmentphotoentrainmententrained
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.
In mammals, such endogenous rhythms are generated by the suprachiasmatic nucleus (SCN) of the anterior hypothalamus.

Pineal gland

pineal foramenpinealpineal body
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.
Light sensitive nerve cells in the retina detect light and send this signal to the suprachiasmatic nucleus (SCN), synchronizing the SCN to the day-night cycle.

Cortisol

stress hormonestress hormoneshydrocortisone
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.
Information about the light/dark cycle is transmitted from the retina to the paired suprachiasmatic nuclei in the hypothalamus.

Retinal ganglion cell

retinal ganglion cellsganglion cellganglion cells
Melanopsin-containing ganglion cells in the retina have a direct connection to the ventrolateral SCN via the retinohypothalamic tract.
They project to, among other areas, the suprachiasmatic nucleus (SCN) via the retinohypothalamic tract for setting and maintaining circadian rhythms.

Photoreceptor cell

photoreceptorsphotoreceptorphotoreceptor cells
The SCN is known to be involved not only in photoreception through innervation from the retinohypothalamic tract but also in thermoregulation of vertebrates capable of homeothermy, as well as regulating locomotion and other behavioral outputs of the circadian clock within ectothermic vertebrates.
These targets include the olivary pretectal nucleus (a center responsible for controlling the pupil of the eye), the LGN, and, through the retinohypothalamic tract (RHT), the suprachiasmatic nucleus of the hypothalamus (the master pacemaker of circadian rhythms).

Pretectal area

pretectumolivary pretectal nucleuspretectal nucleus
The ipsilateral superficial suprachiasmatic nucleus and the medial, dorsal, and lateral terminal nuclei in the midbrain project onto the NOT.

Melatonin

CircadinmelatonergicN-acetyl-5-methoxytryptamine
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.
Light/dark information reaches the suprachiasmatic nuclei from retinal photosensitive ganglion cells of the eyes rather than the melatonin signal (as was once postulated).

PER1

mPER1Per1/Per2period homolog 1 (Drosophila)
Three homologs of PER (PER1, PER2, and PER3) and two CRY homologs (CRY1 and CRY2) have been identified.
PER1 is most notably expressed in the region of the brain called the suprachiasmatic nucleus (SCN), which is the primary circadian pacemaker in the mammalian brain.

Zeitgeber

external environmental time cueZeitgeber (chronobiology)Zeitgebers
Mutations in TIM result in an inability to respond to zeitgebers, which is essential for resetting the biological clock.
It is believed that the brain's suprachiasmatic nucleus (SCN), or internal pacemaker, is responsible for regulating the body's biological rhythms, influenced by a combination of internal and external cues.

PER2

mPer2hPer2Per2'' gene
Three homologs of PER (PER1, PER2, and PER3) and two CRY homologs (CRY1 and CRY2) have been identified.
PER2 is a member of the Period family of genes and is expressed in a circadian pattern in the suprachiasmatic nucleus, the primary circadian pacemaker in the mammalian brain.

PER3

mPER3Period 3period homolog 3 (Drosophila)
Three homologs of PER (PER1, PER2, and PER3) and two CRY homologs (CRY1 and CRY2) have been identified.
It is expressed in a circadian pattern in the suprachiasmatic nucleus (SCN), the primary circadian pacemaker in the mammalian brain.

Time perception

sense of timeperception of timetemporal illusion
One particular component, the suprachiasmatic nucleus, is responsible for the circadian (or daily) rhythm, while other cell clusters appear to be capable of shorter (ultradian) timekeeping.

Shift work sleep disorder

shift work disorderexhaustedshift work
The rhythms are maintained in the suprachiasmatic nucleus (SCN), located in the anterior hypothalamus in the brain, and synchronized with the day/night cycle.

Non-24-hour sleep–wake disorder

Non-24-hour sleep-wake rhythm disorderHypernychthemeralNon-24
Specifically, it is thought to involve abnormal functioning of the suprachiasmatic nucleus (SCN) in the hypothalamus.

Timeless (gene)

timelesstimtimeless (''tim'')
TIM has been identified in mammals; however, its function is still not determined.
While Tim is expressed in the Suprachiasmatic Nucleus (SCN) which is thought to be the primary oscillator in humans, its transcription does not oscillate rhythmically in constant conditions, and the TIM protein remains in the nucleus.

CLOCK

CLKclock genesclock gene
This negative feedback mechanism gives a 24-hour rhythm in the expression of the clock genes.