الفهرس 
Normal sleep PatternOnly 14 pages are availabe for public view
 |  | from | 127 |  |  |
| | | from | 127 | | |
Abstract
Sleep is a state of unconsciousness in which the brain is relatively more responsive to internal than to external stimuli. Sleep proceeds in cycles of REM and the four stages of NREM, following this order: Stages N1 ->N 2 ->N 3 -> N4 -> N3 -> N2 -> REM -> N2. The cycle is repeated again but N1 only occur at the onset of sleep and not repeated. Why we sleep remains one of nature’s greatest mysteries. While sleep may have beneficial effects on general health, its primary function hasn’t fully discovered until now. Several models have been proposed to explain the regulation of sleep and wakefulness. One such model proposes that the regulation of the sleep– wake cycle is governed by two processes: a sleep dependent homeostatic process and a sleep-independent circadian process. Humoral factors, like adenosine, Interleukin-1 beta and Tumor necrosis factor have role in induction and control of sleep. Sleep agonists and antagonists systems modulate our sleep–wake cycle. The timing of the sleep– wake cycle depends on the interaction between sleep agonists and antagonists systems and the suprachiasmatic nucleus. Suprachiasmatic nucleus not only coordinates the timing of the sleep–wake cycle by opposing the sleep agonists but also responsible for circadian timing system.