Stage one is the beginning of the sleep cycle. It is a light stage of sleep. Stage one can be a transition period between wakefulness and sleep. The brain produces high amplitude theta waves. This period of sleep lasts around five to ten minutes.
Stage two is the second stage of sleep and lasts for twenty minutes. The brain begins to produce bursts of rapid rhythmic brain activity known as sleep spindles. The body temperature starts to decrease and heart rate begins to slow.
Stage three was previously divided into stages three and four. Delta waves are deep slow brain waves that begin to emerge during stage three sleep. During this stage, people become less responsive and activity in the environment may fail to generate a response. It also