Circadian Rhythm and the Biological clock.
Our cycle of sleep is also greatly influenced by our biological clocks. For example, if you were put in a cave and had no cues clocks---your body would exhibit a natural rhythm of sleep and walking that closely resembles a 24- to 25- hour cycle. This Phenomenon is referred to as a circadian rhythm. This circadian rhythm is programmed by a group of brain cells in the hypothalamus called the suprachiasmetic nucleus (SCN) (Zee &Manthena, 2007). The SCN works very much like anternal clock, signaling other brain areas when to be aroused (awake) to start the day and when to shut down (sleep) for the day.