Biological timekeeping

This review explains the neurobiology of circadian timekeeping, describing what is known about the master pacemaker for circadian rhythmicity, how biologic systems provide input to the endogenous biologic timing, and how the pacemaker influences physiology and behavior. We discuss how the circadian system can adapt to a changing environment by resetting the circadian clock in the face of a variety of inputs. The genetics of circadian timekeeping are discussed, highlighting what is known about heritable disorders in circadian timing and how circadian genetics have been used to study timekeeping. The role of the clock in peripheral tissues is discussed.