What is the first thing we all do when we feel ill? The answer is we go to bed to sleep. So why is sleep so important for our health? When we sleep, we heal our bodies and minds.
We spend one third of our lives doing nothing but sleeping. But is sleep really doing nothing? It looks like it ... our eyes are closed, our muscles are relaxed, breathing is regular, and we do not respond very much to sound or light. If we look at what is happening inside our brains, however, we find quite a different situation - the brain is very active.
Scientists can record brain activity by attaching electrodes to the scalp and then connecting these electrodes to a machine called an electroencephalograph. The encephalogram(or EEG) is a representation of the brain activity recorded using this machine. The lines of the EEG are what most people know as "brain waves".
Sleep follows a regular cycle each night. The EEG pattern changes in a predictable way several times during a single period of sleep. There are two basic forms of sleep: rapid eye movement(REM) sleep, where we dream, consolidate our thougts and store memories: and non-rapid REM (NREM) sleep, where we produce human growth hormone and heal our bodies. NREM has four different phases where these diverse healing processes take place.
>Infants spend about 50% of their sleep time in REM and 50% in NREM sleep. Adults spend about 20% of their sleep time in REM and 80% in NREM sleep. Elderly people spend less than 15% of their sleep time in REM sleep.
During REM sleep, a person's eyes move back and forth rapidly. Researchers discovered this when they woke people up during REM sleep. Often, when people who are in REM sleep phase are woken up, they say they were just dreaming. The EEG pattern during REM sleep is similar to the EEG pattern when people are awake. However the muscle activity is very quiet during REM sleep. Muscles are inactive to prevent us from acting out our dreams. This also means that sleep walkers are not in REM sleep and are not acting out their dreams.
While we are asleep, our brains are on a bit of a "roller coaster" through different stages of sleep. As we drift off to sleep, we first enter stage 1. After a few minutes, the EEG changes to stage 2 sleep, then to stage 3 sleep, then to stage 4 sleep. Then it's back down again: stage 3, stage 2, then a period of REM sleep ... then, it's back up again, and so on down again, and up again ... you get the picture.
Experiments have shown that the more physical exercise a person does, the more NREM this person experiences. If peop;le are deprived of NREM by being woken up each time they get to stage 4 sleep, they complain about being physically tired. Likewise if people are deprived of stage 5 REM sleep, they are more rlikely to wake up feeling anxious and irritable.
Why sleep at all? It seems like a big waste of time. There is a continuing debate about whay we sleep. Why do most animals sleep? How much sleep is required?
What is important to understand is that sleep has two main functions: to heal and rejuvenate our bodies, and to adapt our brains to the new chanllenges we experience every day.
So, in summary, sleep is important for our health for a number of reasons. It has been shown that we experience one REM sleep stage and four NREM sleep stages. It has also been shown that our bodies do different things during REM sleep compared to NREM sleep. It is during the NREM phases that we heal our bodies, and it is during the REM phase that our brains adap to changes, challenges, and form memories.