Figure 5.

Hierarchical structure of the organismal clock. The suprachiasmatic nucleus (SCN) of the hypothalamus serves as the central clock that entrains the organismal clock by synchronizing the peripheral clocks with the environment. The peripheral organs also have tissue-specific cues related to their functions that can entrain their own clocks independently of the central clock. Reciprocally, the peripheral clocks can feedback to the central clock to further fine tune the organismal clock.