الفهرس 
Basics of SleepOnly 14 pages are availabe for public view
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Abstract
Undisturbed sleep is a sign of good health. Without adequate sleep, our ability to function at our best is impaired. Daytime sleepiness caused by insomnia and other sleep disorders has been called the most underrated health risk factor today.
Many of sleep disorders are associated with medical or psychiatric disorders. Some medical conditions directly affect sleep through the basic disease mechanism; sometimes this relationship is also reciprocal.
Sleep stages are monitored and examined clinically with polysomnography, which provide data regarding electrical and muscular states during sleep. Normal sleep as recorded by EEG consists of two types: REM and NREM, the normal adult human enters sleep through NREM sleep; REM sleep does not occur until 80 min or longer thereafter, and NREM sleep and REM sleep alternate cyclically through the night with a period of about 90 min.
The NREM sleep consist of four stages; stage 1 sleep generally persists for only a few (1 to 7) minutes at the onset of sleep. Stage 2 NREM sleep, signaled by sleep spindles or K complexes in EEG follows this brief episode of stage 1sleep and continues for about 10 to 25 min. Then there is a gradual appearance of high-voltage slow wave activity in EEG. This meets the criteria for stage 3 NREM which usually lasts a few minutes. Stage 4 NREM sleep identified when the high voltage slow wave activity is more than 50 per cent of recorded generally lasts for about 20 to 40 min in first cycle.
Sleep is a vital, highly organized process regulated by complex systems of neuronal networks and neurotransmitters. Changes in sleep and wakefulness are believed to arise from the activity of chemical agents which influence communication between neurons. These chemical agents involve; serotonin which has hypnotic effects and increase delta sleep, norepinephrine which has its neurons in locus coeruleus cease firing in REM sleep and may inhibit REM sleep, acetylcholine its neurons are located in dorsal tegmentum orchestrate REM sleep and together with basal forebrain to inhibit cortical EEG synchronization through influence on thalamus, GABA which has hypnotic effect, dopamine which mediates alerting effects of amphetamine and cocaine.