Dictionary of Human Evolution and Biology

Dictionary of Human Evolution and Biology

Circadian Rhythm

Cycles of metabolic activity and behavior that occur within a 24 h pattern. This daily rhythmicity includes hunger, wakefulness, and sleeping. Some circadian rhythms are influenced by the cycle of light and darkness throughout the year; however, when humans or animals are isolated from the outside environment circadian rhythms remain fairly intact. The mechanism that controls circadian rhythm is the endogenous biological clock.

Cf. infradian rhythm, ultradian rhythm.

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infradian rhythm (... a year. Cf. ultradian rhythm, periodic behavior. See circadian rhythm, rhythmic behavior.)
ultradian rhythm (... 24 h. Cf. infradian rhythm, periodic behavior. See circadian rhythm, rhythmic behavior.)
periodicity (... event; a cycle. See circadian rhythm, circannual rhythm, infradian rhythm, rhythmic behavior.)
biological clock (... , and geophysical periods. See circadian rhythm.)
biorhythm (1. periodic fluctuation or variation of a biological process as a function of time. See ...)