The suprachiasmatic nucleus (SCN) is a tiny region located in the hypothalamus of the brain, precisely above the optic chiasm – where the optic nerves intersect. It serves as the central circadian pacemaker, orchestrating the body’s internal clock and synchronizing various physiological processes to the 24-hour light-dark cycle. The SCN receives direct input from the ipRGCs, allowing it to adjust the timing of sleep, hormone release, and other daily rhythms in response to changes in ambient light.