Sleep is an active, vital brain function. We require sufficient sleep to function optimally while awake. Our mood, our ability to learn and our ability to remain alert while awake depend on a good nights sleep. Sleep enhances other vital body functions including, breathing, heart function, blood circulation, temperature control and normal growth. Normal sleep enhances these functions.
Sleep Structure
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, the first rapid eye movement (REM) sleep appear. REM sleep. REM and NREM sleep then alternate for the rest of the night.
How much sleep we need depends age, sleep efficiency, and how long we 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 hr. of the day.
During the first two years of life sleep becomes consolidated into a single major sleep period, supplemented by an afternoon nap. They spend more time awake than asleep
Sleep is most efficient during early adolescence. Ten-year-olds sleep soundly. They do not nap if they sleep long enough, 9-10 hours each night. They actually grow more when they are asleep than when they are awake!
By age 20 most individuals need about eight hours sleep. That sleep requirement changes very little over the rest of an adults life. A few adults need more sleep. Others need less. Studies show gradual deterioration of several important brain functions when individuals are only partially sleep deprived, nightly for several consecutive nights. Vigilance is reduced. The ability to learn and the capacity to remember become impaired. One's sense of well-being is diminished. Individuals become withdrawn and irritable. Sleep deprived individuals often seem depressed.
Sleep efficiency decreases as we age. More time must be allocated to permit sufficient sleep as sleep efficiency decreases.
Biological Clock
Each of us has a biological clock. This biological clock runs by a molecular mechanism. The clock is present in all animals and has developed over millions of years. An important function of this time piece is to synchronize our wakeful activity with daylight and to promote sleep during darkness. During the light of day substances are secreted by a small cluster of cells that have been identified behind our eyes at the base of our brain. The substances (neurotransmitters) generate an alerting signal that is projected throughout the brain. These alerting neurotransmitters are not produced when it is dark. Melatonin is secreted during darkness. Each complete cycle is a few minutes longer than 24 hours. This cycle it is called our circadian alerting rhythm. Circadian is a combination of two Latin words, circa (near or close to) and dies (day). This circadian rhythm is superimposed on our homeostatic sleep need. To a great extent this rhythm is independent of external influences. However it can be slightly modified 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. The graph below illustrates periodic increases (very tired) and decreases (not very tired) in the tendency to sleep. These individuals need to sleep; the circadian clock modifies how this sleep need affects these individuals.
