A natural inbuilt timer, the circadian rhythm is a 24-hour cycle in all humans, plants, and animals determining sleep and feeding patterns. Circadian rhythms are endogenously generated and can be modulated by external cues such as sunlight or temperature. Nearly all mammalian tissues have functional, autonomous circadian clocks, which must be synchronized to the 24-hour day. This synchronization, also known as entrainment, is hierarchal in … Continue reading The skin keeps time independently of the brain.