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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).
A circadian clock, or circadian oscillator, also known as one’s internal alarm clock is a biochemical oscillator that cycles with a stable phase and is synchronized with solar time. Such a clock's in vivo period is necessarily almost exactly 24 hours (the earth's current solar day). In most living organisms, internally synchronized circadian ...
24-hour physiological rhythms, known now as circadian rhythms, were first documented in 1729 by Jean Jacques d'Ortous de Mairan, a French astronomer who observed that mimosa plants (Mimosa pudica) would orient themselves to be toward the position of the sun despite being in a dark room. [6]
Diurnality is a cycle of activity within a 24-hour period; cyclic activities called circadian rhythms are endogenous cycles not dependent on external cues or environmental factors except for a zeitgeber.
Early research into circadian rhythms demonstrated that, when humans are without zeitgebers, or in constant lighting conditions, they have a "free running" period of 24.9 hours. [7] In this experiment, humans were in an underground, sound-proof bunker where the lights were continuously on.
For example, plant leaves opening and closing at different times of the day or the sleep-wake schedule of animals can all include circadian rhythms. Other periods are also possible, such as 29.5 days resulting from circalunar rhythms or 12.4 hours resulting from circatidal rhythms. [3]
For example, he explains, if you wake up at 6 a.m., "siesta" (six hours later) would be at noon. The history of siestas is rooted in cultures characterized by lengthy daylight periods and warm ...
Modulators of circadian rhythms. In 2021, scientists reported the development of a light-responsive days-lasting modulator of circadian rhythms of tissues via Ck1 inhibition. Such modulators may be useful for chronobiology research and repair of organs that are "out of sync". [26] [27]