Sleep is an active, vital brain function. You require sufficient sleep to function optimally while awake. Your mood, your ability to learn, and your ability to remain alert while awake depend on a good night’s sleep. Sleep enhances other vital body functions including, breathing, heart function, blood circulation, temperature control and normal growth. Normal sleep enhances these functions.
Normal sleep has a characteristic structure and progression. Sleep is comprised of two different states: rapid eye movement sleep (REM) and non-REM (NREM) sleep. NREM sleep occurs at sleep onset and quickly deepens. About 90 minutes after sleep onset, rapid eye movement (REM) sleep begins. REM and NREM sleep then alternate for the rest of the night.
The duration of sleep you need depends upon your age, sleep efficiency, and how long you have been awake. This requirement is referred to as the homeostatic sleep need.
- Infants sleep most of the day and night. They are awake for brief intervals spread over the entire 24-hour day.
- During the first two years of life, sleep becomes consolidated into a single major sleep period, supplemented by an afternoon nap.
- Sleep is most efficient during early adolescence. Ten-year-old children sleep soundly. They do not nap if overnight sleep is sufficient, in most cases between 9 and 10 hours per night. They actually grow more when they are asleep than when they are awake!
- By age 20, most individuals need about eight hours sleep each night. That sleep requirement changes very little over the rest of an adult lifetime. Even small sleep deprivation over several nights can result in the gradual deterioration of important brain functions, including a reduction in the ability to learn and remember, a diminished social capacity and sense of well-being, and an overall lowering of mood.
- Sleep efficiency decreases as we age. More time must be allocated to permit sufficient sleep as sleep efficiency decreases.
Each of us has an internal biological clock which 'runs' by sophisticated operations that take place at the molecular level. One important function of your biological clock is synchronizing your wakeful activity with daylight, and promoting sleep during darkness.
Here’s how it works: during the light of day substances are secreted by a small cluster of cells behind your eyes at the base of your brain. These substances, called neurotransmitters, generate an alerting signal that is projected throughout your entire brain. When the light of day no longer shines, the neurotransmitters are no longer secreted.
Through this synchronization, your biological clock guides your body through regular cycles. One complete cycle lasts a few minutes longer than 24 hours. This cycle is called the circadian alerting rhythm. The word circadian is a combination of two Latin words: circa (near or close to), and dies (day).
To a great extent, the circadian rhythm is independent of external influences. It can, however, be somewhat affected by light, exercise, and social activity. The interaction between our biological alerting clock and our homeostatic need for sleep determines how vigilant we are and how likely we are to fall asleep.