The SCN (suprachiasmatic nucleus) is a small region located in the hypothalamus of the brain. It plays a crucial role in regulating the body's circadian rhythms, which are the natural cycles of physical, mental, and behavioral changes that follow a roughly 24-hour cycle. The SCN receives information about light from the eyes, helping to synchronize the body's internal clock with the external environment. The SCN is composed of about 20,000 neurons and is considered the master clock of the body. It influences various physiological processes, including sleep-wake cycles, hormone release, and body temperature. Disruptions to the SCN can lead to sleep disorders and other health issues.