The suprachiasmatic nucleus (SCN) is a small group of nerve cells located in the brain's hypothalamus. It plays a crucial role in regulating the body's internal clock, known as the circadian rhythm, which influences sleep-wake cycles, hormone release, and other physiological processes. The SCN receives information about light from the eyes, helping to synchronize the body's functions with the day-night cycle. The SCN is often referred to as the master clock because it coordinates the timing of various biological rhythms throughout the body. Disruptions to the SCN, such as those caused by shift work or irregular sleep patterns, can lead to sleep disorders and other health issues.