| Popis: |
In this chapter, the historical development of concepts about sleep and wakefulness is reviewed. Polysomnography is used to record four stages of sleep. Stages N1–N3 correspond to the progressive slowing of brain waves and are the stages of slow-wave sleep. The fourth stage (rapid eye movement [REM] sleep), which resembles a vigil state with eyes closed, contains alpha waves. Three mechanisms have been identified as being responsible for sleep: (1) a process called S (for sleep) that is determined by the individual’s history of sleep and wakefulness, (2) a process called C (for circadian) that is controlled by the endogenous biological clock, and (3) an ultradian component (frequency of approximately 90 min) that is perceptible during both sleep (slow-wave sleep and REM sleep alternation) and wakefulness. Pineal melatonin begins to be released in the late afternoon, at around 6:00 p.m. Melatonin acts on specific receptors located at the suprachiasmatic nuclei, reducing their electrical activity and, hence, their ability to neutralize the S process pressure. Sleep is not just a neurological phenomenon: together with wakefulness, slow-wave sleep and REM sleep comprise three different physiological programs. Sleep deprivation strongly affects the sequence of these physiological programs and leads to cardiovascular disease, metabolic syndrome, obesity, and diabetes types 2 and 3. |
