Horloge biologique et rythme veille/sommeil

Abstract

The biological clock is located in the suprachiasmatic nucleus of the hypothalamus. It influences not only the sleep/wake cycle but also numerous other physiological and biological rhythms (i.e: internal temperature, growth hormone, cortisol and melatonin). The isolation protocols have suggested that the periodicity of the biological clock was above 24 hours. Two main cues are synchronizing the clock on the 24 hour: the social cues and the external bright light. There are not only two but three independent states of sleep and wake: the wake, the slow wave sleep (SWS) and the Rapid Eye Movement (REM) sleep. They are characterized by specific norms of the electroencephalogram, the electrooculogram and the electromyogram. SWS includes four progressive states with more and more slow wave activity (delta power). A night of sleep includes four to six sleep cycles of about 90 minutes. One cycle begins by SWS stage 1 or 2, followed by SWS stage 3 and 4 and ended by REM sleep.