Sleep is controlled by certain chemicals. They build up during the day,eventually reaching levels that make us tired. We can control the effects of these chemicals to some extent.For example,caffeine helps to keep us awake while alcohol and some medicines make us sleepy.
By using electrodes,scientists are able to study what goes on in people's heads while they are sleeping. They have discovered that when we first drop off everything slows down. The heart beats more slowly and our breathing becomes shallow.After about 90 minutes our eyes start to twitch and we go into what is called REM sleep.REM stands for Rapid Eye Movement,and it's a sign that we've started to dream.
You have dreams every night,even if you don't remember them. There are all sorts of theories about why we dream. One is that it gives the brain a chance to sort out the day's activities,filling everything away in the right place. Another is that the brain gets bored while we're asleep and organizes its own entertainment-a sort of late-night cinema!
A lot of people say they have to have eight hours’ sleep every night while others seem to manage on a lot less. One thing is for sure,we all need some sleep and going without it can have some very strange effects. An American DJ,who stayed awake for 200 hours to raise money for charity,thought things were bursting into flames all around him after 120 hours without sleep.He survived the strange horrible period of time but was depressed for three months afterwards.
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