During sleep, the heart beats more slowly, breathing becomes slower, growth hormones peak, muscles relax and body temperature lowers. Newborn infants sleep almost continuously, gradually decreasing their need for sleep. In early childhood, 12 to 13 hours of sleep are generally required and this amount decreases to approximately 8 hours in adulthood.
There are two main stages of sleep classified according to eye movement.The first is rapid eye movement which is a shallow, dream-filled sleep.
During this time the muscles relax while the brain produces irregular wave activity.
and brain waves become larger as the body is asleep. where growth hormones peak, and cell and tissue repair take place.
Every 90 minutes the brain enters the dream sub-stage, where brain wave activity is similar in pattern to being awake, but muscles are not able to move as when awake. This stage lengthens each repeated cycle during the night, and is crucial to preserving mental health and long term memory, since the brain sorts through short term memory and 'deletes' unimportant data.
The second major stage of sleep is non rapid eye movement, where blood pressure drops and heart rate slows as the person enters a deep sleep.