ge 3 and 4, growth hormone is secreted by the pineal gland. This hormone encourages bone and muscle growth in children, while in adults it is involved in tissue repair. This is one reason why slow wave sleep has restorative effects. Other hormonal activities, like the secretion of prolactin and gonadotropin occur in these stages, making slow wave sleep a phase of rest and healing.
             "REM" Sleep (Rapid Eye Movement)
             Once stage four is complete, the person will then cycle back through stages 3 and then 2 before finally reaching REM sleep. At this point our muscles are very relaxed; in fact, we become paralysed. We are mostly disconnected from the outside world, but we might wake up to something meaningful like our names being called out, or loud sounds. A single REM cycle lasts about 20 to 30 minutes in a healthy person in his/her twenties. As REM sleep occurs during every ninety-minute interval after we fall asleep; this means that in an 8 hour sleep we will experience
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