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Sleep is one of the essential routines in our daily lives. We start to feel a bit drowsy as the clock reaches a certain time and we know it is time to lie down and close our eyes for a while. We have to sleep so that our bodies can refuel for the next day. Sleep is something that is simply programmed into our bodies. We know this because it is commonly seen that people eventually sleep even if they don't want to! This is because their bodies simply demand it.

Sleep goes on for roughly one-third of our total life which shows how important it really is. It is an important activity that, if not spent wisely, will eventually detract from your work and cause severe problems in your life. People just aren't as good at anything as they are when they have had enough sleep. We know that we should not neglect our sleep because it is crucial for our motor and our cognitive functions. In order for us to survive in this world, we simply need to sleep.

In a test on rats, those who were deprived of sleep died within two to three weeks. Scientists have learned that it is crucial for both animals and people to sleep in order to be alert and functioning each day. In scientific terms, we now know that the activity of the brain regulates the amount of sleep that is needed by the body. Researchers use electrodes and electroencephalograms (EEG's) to measure electrical activity in the brain, eye movement, and muscle tension. These are all examined to determine many facts about sleep in general. The results show certain patterns which then lead to finding out about the various stages of sleep.

There are two basic stages of sleep which are rapid eye movement (REM) and non-rapid eye movement (NREM). NREM sleep is composed of four stages in terms of the amplitude and frequency of the activity of the brain waves. The pattern of NREM sleep on the brain waves is slower, more regular, and of a higher voltage than that of wakefulness. When you are in a deep sleep, the brain waves move slower and have bigger amplitude. The first stage of NREM sleep is very light sleep. Stage two NREM, however, has two kinds of brain waves that are present. They are called sleep spindles and K complexes. Stage three and four of NREM has incrementally higher voltages and slower waves. By stage four NREM, it is extremely hard to wake a person up. This could also be referred to as 'sleeping like a log'.

REM sleep is the second basic stage of sleep. It is described by eye movements that bounce around underneath a person's eyelids in an extremely rapid fashion. The eye movements do not necessarily move all the time but they may suddenly zoom up and down or back and forth, stop for a while and then dart back and forth again intermittently. During REM sleep, the activity shows very fast and irregular activity. It is a lot more spontaneous than in the NREM sleep. The person's muscle tone also goes limp although the major muscles like the heart, diaphragm, eye muscles and

blood vessels are still active. The state of the body in this stage is almost like being paralyzed. This is because the electrical activities in the muscles are almost completely stopped. There may be some small twitching in these muscles but mostly there is nothing during this stage.

Sleep is a cyclical process where NREM and REM sleep will repeat in cycles. It starts with an NREM phase which last for roughly ninety to one hundred and ten minutes. Then it recurs four to six times per night. As the night progresses, the extent of NREM sleep decreases and the extent of REM sleep increases. Also, blood flow to the brain, airway resistance, sexual arousal, respiration and blood pressure increase. Sleep is a broad topic and it is intimately connected to a person's age in how it functions. Biological clocks, homeostasis, dreams, and sleep practices all play a part in how living things sleep. The science of sleep is so complex that we should all take care to get the correct amount of sleep. It is one of the most important things you will ever do!