Chapter 40 - Central and Peripheral Circadian Clocks

Abstract

The master clock in the suprachiasmatic nucleus (SCN) controls the sleep-wake cycle and hormonal rhythms, as well as a multitude of other circadian rhythms. The SCN clock conducts the multitude of brain and peripheral clocks to ensure circadian temporal organization and its adjustment to the daily variations of the environment. Rhythmic signals from the SCN couple the master clock to secondary brain and peripheral clocks through behavioral, nervous, and neurohumoral pathways. Endocrine rhythms (e.g., pineal melatonin and adrenal glucocorticoids) distribute internal temporal messages within the body. Light perceived by the retina is the most potent synchronizer of the master clock in the SCN, whereas most brain and peripheral clocks can be shifted as a function of mealtime as well as the timing of sleep. Circadian clocks and intracellular metabolism are tightly and reciprocally connected.