Figure 3.

Parallel pathways synchronize peripheral clocks to the LD cycle. Light is the most important zeitgeber for circadian clocks and can reach peripheral clocks via several routes. In pathway 1, light from the retina reaches the SCN through the retino‐hypothalamic tract and entrains the SCN clock that then transmits the timing information to peripheral clocks along neuronal and/or endocrine pathways. Pathway 2 depicts additional routes for transmission of photic information that bypass the SCN clock and directly or indirectly reset peripheral clocks.