Abstract

A circadian clock cycles with a stable phase that is synchronized with solar time and organizes physiological functions with a 24-hour period. In mammals, the circadian system consists of a collection of oscillators that operate at the systems, tissue, and cellular levels. Located in the suprachiasmatic nucleus (SCN) of the hypothalamus is the central clock, which acts as a central pacemaker for rhythms observed in behavior, body temperature, and hormones. The SCN consists of a large population of oscillator neurons. Together, these neurons produce a coherent signal that drives the body's circadian rhythms. What properties of the cell-to-cell communication allow the synchronization of these neurons, despite a wide range of environmental challenges such as fluctuations in photoperiods? Also present in most organs and systems (e.g., kidney and the immune system) and cells are peripheral clocks that can oscillate independently of the SCN. How do the circadian clocks regulate organ function, and how does that differ between males and females?