The biological clock that keeps track of this cycle is located in the middle of the brain, called the suprachiasmatic nucleus. For playing such a crucial role in regulating the entire system, the suprachiasmatic nucleus is relatively small, as it is composed of 20,000 brain cells. This number may seem significant, but the brain is made up of over 100 billion neurons.
This tiny mind clock is what regulates the circadian rhythm, activating and deactivating both brain and body mechanisms based on this twenty-four-hour span.