Morphology and function of the circadian clock

As an introduction to the Leopoldina satellite symposium on Chronobiology, the morphology and function of the mammalian circadian clock are briefly summarized. The clock is epitomized as circadian (from circa diem) as its endogenous period length is not exactly, but close to 24h. The central master clock is of paramount importance as it regulates e.g. locomotor activity, the sleep-wake cycle and hormonal rhythms. Peripheral clocks will not be considered. The present review draws heavily on animal studies, because in humans the actual clock mechanisms are difficult to explore. The central master clock consists of…