achim kramer lab
Biological rhythms with a period of about 24h are called circadian rhythms (from Latin circa dies which means "about a day"). Circadian rhythms are present on all levels of complexity, from gene expression to rhythms in physiology, metabolism and behavior. They are generated by an internal timing system - an endogenous circadian clock, which allows organisms to anticipate the daily changes in their environment. Light acts as the primary stimulus to synchronize the internal clock with the outside world. In mammals, circadian clocks have been found in mostly every cell, but they are hierarchically organized: A tiny brain structure, the suprachiasmatic nucleus (SCN) of the hypothalamus is known as the master-pacemaker. Specialized neurons within the retina perceive the light and transmit this information via the retinohypothalamic tract to the SCN. Periphereral clocks in other tissues are entrained by the SCN and are most likely responsible for regulating rhythms in physiology and behavior locally.