A circadian rhythm is a roughly 24 hour cycle in the physiological processes of living beings, including plants, animals, fungi and cyanobacteria.
In a strict sense, circadian rhythms are endogenously generated, although they can be modulated by external cues such as sunlight and temperature.
Circadian rhythms are important in determining the sleeping and feeding patterns of all animals, including human beings.
There are clear patterns of brain wave activity, hormone production, cell regeneration and other biological activities linked to this daily cycle.
