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Biological rhythms are repetitive biological processes. [1] Some types of biological rhythms have been described as biological clocks. They can range in frequency from microseconds to less than one repetitive event per decade. Biological rhythms are studied by chronobiology.
Overview, including some physiological parameters, of the human circadian rhythm ("biological clock"). Chronobiology is a field of biology that examines timing processes, including periodic (cyclic) phenomena in living organisms, such as their adaptation to solar- and lunar-related rhythms. [1] These cycles are known as biological rhythms.
The first published usage of the term "phase response curve" was in 1960 by Patricia DeCoursey. The "daily" activity rhythms of her flying squirrels, kept in constant darkness, responded to pulses of light exposure. The response varied according to the time of day – that is, the animals' subjective "day" – when light was administered.
The rhythm persists in constant conditions, i.e. constant darkness, with a period of about 24 hours. The period of the rhythm in constant conditions is called the free-running period and is denoted by the Greek letter τ (tau). The rationale for this criterion is to distinguish circadian rhythms from simple responses to daily external cues.
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.
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 ...
Empirically, it is an ultradian rhythm of approximately 90 minutes (80–120 minutes [2]) characterized by different levels of excitement and rest. The cycle is mediated by the human biological clock. It is most readily observed in stages of sleep, for example, rapid eye movement sleep (REM) and the delta activity cycle.
Biological rhythm, repetitive cycles that occur in biology, studied in the science of chronobiology; See also. Chronobiology This page was last edited on 30 June ...