Final answer:
The suprachiasmatic nucleus (SCN) is located in the hypothalamus and functions as the body's internal clock, establishing the circadian rhythm based on light information received from the retina. It regulates sleep/wake patterns and other physiological processes.
Step-by-step explanation:
The suprachiasmatic nucleus (SCN) is a cluster of cells located in the hypothalamus of the brain. It serves as the body's internal clock, helping to establish the circadian rhythm based on the presence or absence of daylight. The SCN receives information from light-sensitive neurons in the retina, allowing it to synchronize the internal clock with the outside world. This synchronization is important for regulating sleep/wake patterns, hormone release, and other physiological processes that occur at specific times each day.