Sleep 1/22/2021

Why do we sleep?

Why do we sleep?

In this course, you’ll learn about the mysterious concept of sleep, the sleep patterns of different animals and why we all need good sleep!

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Sleep is one of the greatest enigmas of the human body. It is a vulnerable state (we are basically unconscious!) for us to spend so much time in.

Our bodies wouldn’t spend so much time in the vulnerable state of sleep if it weren’t important to our health.

Today we know that sleep is an essential brain function.

Sleep is as essential to your health and survival as water is.

Total sleep deprivation can be fatal within 12 days.

But why do we need sleep?

Scientists still don’t fully know the answer to this question. But we can learn a lot by looking at the sleep patterns of other animals.

Every animal that we know of sleeps in one form or another. But their sleep patterns depend a lot on their environments – and on the demands of their brains.

Animals with big, complex brains for their body size need to supply their brains with a lot of energy.

They also tend to need more sleep – particularly more deep sleep.

Sleep supports complex brains in many ways. Sleep saves energy for brain activity.

Deep sleep strengthens new connections between brain cells, which helps with memory.
This may be why animals with complex brains (like you!) need more deep sleep.

Your brain is very good at forming new connections between brain cells, which helps you learn!

Your brain strengthens these connections while you sleep.

But not all animals with complex brains keep the same sleep patterns. Their sleep patterns also depend on their environments, eating patterns and dangers they face.

Sleep can be fatal for dolphins in the ocean - they need to be awake to swim and breathe!

But dolphins have found an amazing solution to their need for sleep in the water. Half of their brain (one hemisphere) can be sleeping while the other half is awake or alert!

This is how a dolphin can rest its brain but still breathe, swim, keep its body warm and watch for potential dangers! It puts only half of its brain to sleep at a time.

By sleeping with half of their brains, dolphins can get deep sleep while also migrating long distances to find food and to breed.

For other animals, sleep is risky because it is a time when they can get attacked by predators.

Rats sleep upwards of 20 hours each day – but in short bursts of lighter sleep. By sleeping in short bursts, rats can stay alert to avoid predators and forage for more food.

Rats have much simpler brains than dolphins or humans. But they still need to sleep to strengthen new connections between their brain cells, so that they can learn.

But while dolphins sleep on the go and rats sleep in short bursts all day long, we humans pack all of our sleep into a long overnight slumber.

Why is that?

Like dolphins and rats, we developed our sleep pattern to best suit our survival needs - and our very big, complex brains.

Unlike dolphins, we put our whole brains to sleep at night for many hours at a time – ideally 7 to 8 hours! This sleep pattern has many advantages.

Sleeping all night under shelter historically helped us stay hidden from nocturnal predators.

Our precise color vision is also poorly adapted to the dark. We’ve always seen better during the day to hunt and work – so we sleep at night when our vision is poor.

But most importantly, we support our big, complex brains by sleeping all night.

For your brain to work at its best, it needs plenty of energy. It also needs time to repair damage and strengthen its learning muscles – connections between brain cells.

Lifting weights helps you to build strong muscles. But your muscles actually grow by repairing
micro-damages when you are resting, not when you are exercising.

Your body repairs itself while you sleep. Your brain does the same. And this repair works better when you sleep deeper for longer, rather than lighter and in short bursts like a rat!

Deep sleep is critical for learning and memory, but also for mental health.

Sleep helps remove toxins from your brain and strengthens connections between your brain cells. This improves your brain function.

Not sleeping for long enough or deep enough can hurt your ability to remember things, make you more impulsive and put you at risk for depression and dementia.

Now you know the reasons why we humans sleep through the night – because it's the best time to help us power and build our big, complex brains.


If you are an adult, you need
7-9 hours of sleep every night to stay healthy in your body and in your brain. Sleep is critical for brain function.

Sleep also replenishes energy and repairs damage throughout your body. Sleep deprivation can put you at risk of heart disease, diabetes and obesity, as well as cognitive disorders.
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