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A circadian rhythm (/ s ər ˈ k eɪ d i ə n /), or circadian cycle, is a natural oscillation that repeats roughly every 24 hours. Circadian rhythms can refer to any process that originates within an organism (i.e., endogenous ) and responds to the environment (is entrained by the environment).
An actogram is a plot that shows rhythms in biological variables throughout the day. Traditionally, actograms describe phases of activity and rest, but they have also been used to visualize rhythms in protein phosphorylation, gene expression, and hormone secretion.
In vertebrates, the master circadian clock is contained within the suprachiasmatic nucleus (SCN), a bilateral nerve cluster of about 20,000 neurons. [10] [11] The SCN itself is located in the hypothalamus, a small region of the brain situated directly above the optic chiasm, where it receives input from specialized photosensitive ganglion cells in the retina via the retinohypothalamic tract.
A-riot-of-rhythms-neuronal-and-glial-circadian-oscillators-in-the-mediobasal-hypothalamus-1756-6606-2-28-S3. Sleep and memory have been closely correlated for over a century. It seemed logical that the rehearsal of learned information during the day, such as in dreams, could be responsible for this consolidation. REM sleep was first studied in ...
A zeitgeber (/ ˈ (t) s aɪ t ɡ eɪ b ər, ˈ z aɪ t-/ (T)SYTE-gay-bər, ZYTE-, German: [ˈtsaɪtˌɡeːbɐ]) is any external or environmental cue that entrains or synchronizes an organism's biological rhythms, usually naturally occurring and serving to entrain to the Earth's 24-hour light/dark and 12-month cycles.
The bunker experiment conducted by Aschoff demonstrated that the participants' urine excretion, rectal temperature, and circadian rhythm of activity all had a free running period of approximately 25 hours in the absence of external cues. [3] Furthermore, it was established that men typically have a slightly longer period than women. [3]
In the brain, NPAS2 functions as a generator and maintainer of mammalian circadian rhythms. More specifically, NPAS2 is an activator of transcription and translation of core clock and clock-controlled genes through its role in a negative feedback loop in the suprachiasmatic nucleus (SCN), the brain region responsible for the control of ...
Hardin and colleagues (1990) were the first to propose that the mechanism driving these rhythms was a negative feedback loop. Subsequent major discoveries confirmed this model; notably experiments led by Thomas K. Darlington and Nicholas Gekakis in the late 1990s that identified clock proteins and characterized their methods in Drosophila and ...
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