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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).
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.
The best studied rhythm in chronobiology is the circadian rhythm, a roughly 24-hour cycle shown by physiological processes in all these organisms. The term circadian comes from the Latin circa, meaning "around" and dies, "day", meaning "approximately a day." It is regulated by circadian clocks.
Circadian clock, a molecular mechanism that results in a circadian rhythm in a living organism; Circadian rhythm, biological process that displays an oscillation about 24 hours, such as the human sleep-wake cycle (the "body clock") Epigenetic clock, a set of DNA sites whose methylation levels can be used to measure aging throughout the body
Description: Overview of biological circadian clock in humans. Biological clock affects the daily rhythm of many physiological processes. This diagram depicts the circadian patterns typical of someone who rises early in morning, eats lunch around noon, and sleeps at night (10 p.m.).
Biological rhythms are endogenous; they persist even in the absence of environmental cues as they are driven by an internal mechanism, most notably the circadian clock. Of the several possible cues (known as zeitgebers, German for 'time-givers') that can contribute to entrainment of the circadian clock, light has the greatest impact.
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More specifically, it is a necessary component for the expression of numerous behavioral and physiological circadian rhythms. The dorsomedial hypothalamic nucleus receives information from neurons and humors involved in feeding regulation, body weight and energy consumption, and then passes this information on to brain regions involved in sleep ...