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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".
The nucleus of a Type 2 pinealocyte contains many infoldings which contain large amounts of rough endoplasmic reticulum and ribosomes. [6] An abundance of cilia and centrioles has also been found in these Type 2 cells of the pineal gland. [7] Unique to the Type 2 is the presence of vacuoles containing 2 layers of membrane. [7]
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. [4]
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 ]
The suprachiasmatic nucleus functions as the hypothalamic master clock, controlling the body's Circadian rhythm. The suprachiasmatic nucleus of mice, hamsters, and rats have a small amount of cholinergic innervation. [8] A "time memory" is the memory at a specific time of day for which an individual made an association with a certain event or ...
The “master clock” for circadian rhythms in mammals is the suprachiasmatic nucleus (SCN). The SCN has little if any projection directly to the VLPO neurons. Instead, they project strongly to the adjacent subparaventricular zone, which in turn contains inhibitory GABAergic neurons that innervate the dorsomedial nucleus of the hypothalamus.
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, but it is also possible that it contains its own feeding-entrained oscillator (FEO).