Exactly what makes a person lose consciousness and fall asleep remains a mystery. Researchers, however, have established that sleep is a complex process regulated by the brain and that it obeys a 24-hour biological clock.
The production of growth hormone peaks during sleep
As we get older, our sleeping habits change. A newborn sleeps for frequent short periods that total about 18 hours a day. According to sleep specialists, although some adults appear to need only three hours of sleep a day, others need up to ten hours.
Recent research has shown that variations in our biological clock also explain why some teenagers struggle to get out of bed in the morning. The biological clock seems to shift forward during puberty, making youngsters want to go to sleep later and wake up later. This sleep delay is common and tends to disappear in the mid-to-late teens.
Our biological clock is regulated by chemical substances, many of which have already been identified. One of them is melatonin, a hormone thought to trigger sleepiness. Melatonin is produced in the brain, and some scientists believe that it is responsible for the slowdown of the body's metabolism that occurs prior to falling asleep. As melatonin is released, body temperature and blood flow to the brain are reduced, and our muscles gradually lose their tone and become flaccid. What happens next as the person descends into the mysterious world of sleep?
Nature's Chief Nourisher
Approximately two hours after we fall asleep, our eyes begin to quiver quickly back and forth. The observation of this phenomenon led scientists to divide sleep into two basic phases: REM (rapid eye movement) sleep and non-REM sleep. Non-REM sleep can be subdivided into four stages of progressively deeper sleep. During a healthy night's sleep, REM sleep occurs several times, alternating with non-REM sleep.
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