Definition: The natural pattern of physiological and behavioral processes that are timed to a near 24-hour period. These processes include sleep-wake cycles, body temperature, blood pressure, and the release of hormones. This activity is controlled by the biological clock, which is located in the suprachiasmatic nuclei of the hypothalamus in human brains. It is highly influenced by natural dark-light cycles, but will persist under constant environmental conditions.
Disruptions to the circadian rhythm can cause problems with the sleep-wake cycle.