Biological Clock and its Entrainment by Photoperiod

Abstract

As we know today, our biological master clock is located in the supperachiasmatic nuclei (SCN) of the hypothalamus and is entrained mainly by light/dark (L/D) cycles; it also acts as our internal calendar. The modus operandi of our biological clock was considered, for many years, as a black box. Our understanding of the biological clock functioning came from experiments in which subjects were exposed to light during the subjective night, which resulted in a phase shift, while such a shift was not detected when exposure to light took place during the subjective day. As we also know today, the molecular basis of the biological clock is based on interactions between various clock genes paired to create hetero-dimmers and are templates for proteins production that interact with genes by positive and negative feedback loops.

Chronos is the personification of Time, who is often depicted as man turning the Zodiac Wheel.

Greek mythology