We sleep at night because our bodies are adapted to be active during the day. Other animals, such as bats or badgers, sleep during the day and are active at night because this is when they hunt to find their food.
We have good eyesight when there is plenty of light, but at night we see poorly and find it difficult to get around. Bats and badgers have poor eyesight, and use sound and smell to find their way around at night. But this does not explain how our pattern of sleep is controlled.
The brain tells us when to sleep. Deep in the brain is a biological clock consisting of about fifty thousand nerve cells that work together and act a bit like an alarm clock, telling the rest of the body what to do at different times of the day, and when we should be asleep or awake. Tiredness is also controlled by another part of the brain, which measures how long we have been awake. The longer we are awake the more tired we feel.
Flying to other countries thousands of miles away in different time zones gives us jet lag. When it is daytime in Australia it is night-time in England, and when we are going to bed in England, people are getting up in California. Our body clock cannot adjust to the new time zone instantly. It takes several days. So you feel tired or hungry at the wrong times in Australia or California until the clock in the brain moves from home time to the new time zone. We recover from jet lag because light in the new time zone, detected by the eye, regulates our body clock.
So the body clock and levels of tiredness work together to regulate our sleep patterns. Many people think that the brain is turned off during sleep, but this is wrong. Some parts of the brain are even more active during sleep than when we are awake! This is because during sleep the brain is helping us to remember what has happened during the day and to make sense of new information. Many people wake up in the morning and find they have the answer to a problem that has been puzzling them for ages!
The rest of the body also undergoes lots of changes while we are asleep. Young people grow more during sleep than when they are awake, and damage to the body is often repaired at night. When we are young we need about nine hours of sleep each night for the brain to be fully active during the day.
You are better at solving problems, less moody, better at sport and will even find jokes funnier with a good long sleep. Many grown-ups do not get enough sleep, sleeping only five or six hours each night. If this goes on too long, they can become seriously ill with conditions that can affect their digestion or heart and they might even suffer from depression.
For a long time we did not realise why sleep is so important. Now we know that lots of helpful things are going on in our bodies during sleep. Sleep helps make us both healthy and happy. So make sure you get enough sleep!
