Hypothalamus acts as a master clock in the human body. The master circadian clock that regulates 24-hour cycles throughout our bodies is found in a region called the suprachiasmatic nuclei (SCN) in the hypothalamus of the brain. The SCN is made up of two tiny clusters of several thousand nerve cells that "tell time" based on external cues, such as light and darkness. The SCN regulates sleep, metabolism, and hormone production.