What Are the Cycles of Sleep?

A person generally sleeps in a prone position, or in as relaxing a position as possible if lying down isn't an option. His eyes close, his breathing slows down and become rhythmic, and his muscles gradually relax. Muscle movement is possible during sleep but is usually a sign of the body repositioning itself so that no part has its circulation cut off for too long of a time.

According to the Sleep Channel, there are five sleep cycles. When a person is awake but relaxed, she drifts into stage one sleep. Her muscles start off tense but relax as she nears the sleep state. Her eyes move erratically, then slow down to a roll. Cycle one is drowsiness. Her eyes close, but although she has entered a sleep stage she can be easily aroused. If she wakes up from this part of the cycle, she will not feel rested. Cycle one lasts about 5 to 10 minutes. Cycle two is light sleep that includes spontaneous periods of muscle movement, combined with periods of relaxation. This cycle prepares the body for the deeper stages, with body temperature and heart rate both going down. Polysomnographic readings taken during this cycle show peaks and valleys in the brain waves. Cycles three and four are the deepest stages of sleep. They consist of delta, or slow-wave, sleep. Although these cycles are similar, cycle four is deeper and more intense. During this period, an electromyogram will show slow, high-amplitude waves. Cycles one through four are non-REM sleep, meaning that there are no rapid eye movements during these phases Altogether, these cycles last from about 90 to 120 minutes. Cycle five is the period of rapid eye movement, or REM, sleep. Besides the eye movement, this cycle is distinguished by other physical symptoms, such as faster breathing and twitching of the fingers, legs and face. There is heightened brain activity, which results in intense dreaming, but the major voluntary muscle groups are paralyzed during this cycle. Some researchers believe that the paralysis is a way of preventing a person from acting out what is going on in dreams. Several periods of REM occur during cycle five. The first lasts for about 10 minutes, and each lasts a little longer, with the final period lasting an hour.

Sleep gives a person physical and mental downtime. It's a time in which energy is conserved. The body doesn't need to eat or drink because it's in a resting state and is not expending much energy. During the cycles of sleep, the body is able to replace aging and dead cells and to heal and repair tissues, organs and muscles. Regular, good-quality sleep keeps the immune system healthy, and growth hormone is excreted during this time in children. Some researchers also believe that the brain uses dreams to organize memories during sleep time.

Sleep has a healthy, restful effect on the mind and body. Most people wake up feeling rested and ready to face a new day. Conversely, according to the Harvard Medical School, sleep deprivation has negative effects on physical and mental health. After one night of missed sleep, a person usually slows down and feels irritable. After a second missed night, she will have trouble concentrating. By the third day, she will not be able to think clearly and may eventually start to hallucinate. She will be more vulnerable to illness because her immune system will be compromised.

If you want to ensure that you get good quality sleep that encompasses all five cycles, Harvard Medical School recommends a number of tips: *Create and stick to a regular sleep schedule. Get up at the same time every morning, and go to sleep at the same time every night. *Drown out annoying noises with a fan or white noise machine. *Don't use caffeine or drink alcohol before bedtime. It's best to cut out the caffeine at noon. *Use heavy curtains to keep out light if you are waking up too early *Don't do vigorous exercise shortly before bedtime, and don't eat a heavy meal or drink too much liquid.