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The suprachiasmatic nucleus or nuclei (SCN) is a small region of the brain in the hypothalamus, situated directly above the optic chiasm. It is responsible for regulating sleep cycles in animals. [ 1 ] [ 2 ] Reception of light inputs from photosensitive retinal ganglion cells allow it to coordinate the subordinate cellular clocks of the body ...
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. [ a ] [ 2 ] The suprachiasmatic nuclei receive and interpret information on environmental light, dark and day length, important in the entrainment of the "body clock".
They send light information via the retinohypothalamic tract (RHT) directly to the circadian pacemaker of the brain, the suprachiasmatic nucleus of the hypothalamus. The physiological properties of these ganglion cells match known properties of the daily light entrainment (synchronization) mechanism regulating circadian rhythms. In addition ...
A circadian rhythm is an entrainable, endogenous, biological activity that has a period of roughly twenty-four hours. 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. [3]
The suprachiasmatic nucleus in the hypothalamus is responsible for this cycle of secretion from the epithalamus, specifically from the pineal gland. [8] The Circadian timekeeping is driven in cells by the cyclical activity of core clock genes and proteins such as per2/PER2. [ 9 ]
Czeisler investigates how the physiological system works to reset the human central circadian pacemaker, located in the hypothalamus and called the suprachiasmatic nucleus (SCN). [7] Among his most salient contributions to this research area are a pair of seminal Science original research articles published in 1986 [8] and 1989. [9]
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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. Genes in this family encode components of the circadian clock, which regulates the daily rhythms of locomotor activity, metabolism, and behavior.