Understanding sleep

Understanding sleep

Why do we sleep?
We have to sleep because it is essential to maintaining normal levels of cognitive skills such as speech, memory, and flexible thinking. In other words, sleep plays a significant role in brain development.

Normal sleep
Contrary to what is often thought, sleep is an active, organised process. How and when we sleep is governed by a number of factors. These include factors under our control, and factors beyond our control. Chief among those beyond our control is our biological clock that regulates our internal rhythm over a 24-hour period. Sleep is also regulated by different areas of the brain.

Sleep occurs in stages, which happen at different times during the night. There are two major divisions - rapid eye movement (REM) sleep, and non-rapid eye movement (non-REM) sleep. Non-REM sleep is in turn further divided into four different stages with stages 3 and 4 often referred to as "deep sleep." In adults, non-REM sleep occupies around 80 percent of the night, and REM sleep 20 percent. However, REM sleep does not occur in one large block - REM sleep occurs around once every 90 minutes. The first rapid eye movement (REM) period usually begins about 70 to 90 minutes after we fall asleep. We have around three to five REM episodes a night. After REM sleep, the whole cycle begins again.

Non-REM and REM sleep
During non-REM sleep, many of the restorative functions of sleep occur. Hormones are released which help the body rebuild itself from damage done during the day.
During REM sleep, memories and thoughts from the day are processed. Although we are not conscious, the brain is very active - often more so than when we are awake. Our eyes dart around (hence the name), and our breathing rate and blood pressure rise. This is the period when most dreams occur. The purpose of dreaming is not well understood, but it probably relates to processing mental information that was received during the day. During REM sleep, we normally lose the use of our limb muscles. Thus, our bodies are effectively paralysed, said to be nature's way of preventing us from acting out our dreams.

How much sleep do I need?
There is a wide range of sleep time that is considered "normal", as it varies from person to person. While the average normal amount of sleep is around 7.5 hours per night, there are some people who do just fine on 5 hours per night, and some who require as much as 9 hours per night. The key is to find the right amount for you. The best way to tell is by seeing how you function during the day. For example, if after 6 hours of sleep you feel refreshed in the morning and awake during your daylight hours, then you don't need more than that. If, on the other hand, you need 9 hours a night to feel refreshed and to function well during the day, then that is what your individual requirement is and sleeping the "normal" amount of 7.5 hours per night will actually leave you sleep deprived. If you are getting what you consider to be an adequate amount of sleep and are still unrefreshed and sleepy, then you might have a sleep disorder and should consider seeking professional consultation.


This information is based on content from the following websites:
The University of Maryland Medical Centre.
The BBC's Human Body and Mind.

All advice is either supported by references (cited in the text) or is based upon peer reviewed professional opinion. Our advice is impartial and not influenced by sponsors or product suppliers listed on the site.
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