Why do we need to sleep?

We spend roughly one third of our lives asleep.  Have you ever wondered why we need to sleep?

At one level this may feel obvious – we go to sleep when we are tired to rest and we (ideally!) wake up feeling regenerated for another day. We all know that if we go without enough sleep for too long we can feel terrible, fragile and emotional. Our thinking and reactions times suffer and if we become too sleep deprived we struggle to carry out even simple tasks. What we don’t yet know is exactly what occurs in the brain while we sleep.

 

One theory is that sleep plays a major role in learning and memory. People suffering from lack of sleep can struggle to recall information easily. Neurons are a type of cell in the brain designed to transmit information. There are an estimated 10-20 billion of them in the human brain. Research has shown that when animals learn a new task the connections between the neurons in the brain involved in learning that task appear to strengthen when they are next asleep.

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Don't read your smartphone or tablet in bed!

It stops your mind relaxing and the  artifical light reduces melatonin production

Another role of sleep could be when the brain cleans out toxins. The brain consumes a lot of energy and produces a lot of waste. The gaps between brain cells expand during sleep aiding the removal of waste.

 

How much sleep do we need?

Eight hours a night in the traditional standard. Everyone varies but for regular adults around seven to nine hours a night is ideal. You can get by on a bit less for a short while but will soon start to feel the ill effects.

Why do we sleep at night time?

Sleeping for roughly one third of our lives (if we get those 8 hours a night!) was an evolutionally risky business.  Think about early human history out on the savannah hunting and being hunted.  How does it make sense to go to sleep and making yourself much more vulnerable to attack?

The Circadian Rhythm

The change between day and night as the Earth rotates on its axis has been a constant feature during human evolution.   This cycle of roughly 24 hours drives biological processes in humans as well as in other animals, insects and plants. Such a process is called a circadian rhythm.   

This cycle between day and night helps regulate the amount of a number of compounds in the body that together promote going to sleep or waking up.  Two of these most important compounds are melatonin and adenosine, the build-up in our bodies makes us feel sleepier and sleepier.

Morning daylight creates signals in the brain that result in an area called the pineal gland to stop the production of melatonin causing levels in our body to fall and helping us to wake up.  As night falls the pineal gland starts to produce melatonin and the level in our body builds up making us feel sleepy.  

As the day progresses the brain uses more and more energy resulting in the production of adenosine. Adenosine binds to many neurons in the brain causing them to reduce activity and the individual to fall asleep.  During sleep the brain uses less energy and the adenosine levels decline leading to waking up and the daily cycle starting again.