Appliance of science: What's inside our brains?

Dr Naomi Lavelle gets inside our heads and tells us all about what’s in there.

Appliance of science: What's inside our brains?

What is inside our brains?

Five year old Jacob wants the low down on our grey matter!

Firstly, the term grey matter is not completely correct; a healthy living brain can have a light pink colour with certain parts referred to as the grey matter and the white matter. The brain is a large clump of nerve cells, called neurons, about 86bn of them in total.

This bit is the grey matter and is arranged into different areas that are responsible for memory storage, emotions, movement and many other functions. There are also billions of nerve fibres in the brain, the part called the white matter, which connect all the different regions of grey matter together.

The brain also contains fat, water and a rich supply of blood vessels. Our brains are like computers, they store information and control how we feel, what we think and what we do. They are not fully developed until our mid 20s.

Do all animals have brains?

No they don’t. Some like sea sponges, jellyfish and starfish don’t.

What animal has the biggest brain?

The sperm whale has the heaviest brain, a whopping 8kg in weight on average! An adult human brain weighs about 1.5kg, about the same as a dolphin’s.

Are bigger brains a sign of more intelligence?

There was a theory that the bigger the brain, the more intelligent the animal, but this is not the case.

Elephants and whales have larger brains than humans but we certainly don’t consider them more intelligent than us. (When talking about brains and intelligence we usually compare cognitive ability which, put simply, is the ability to learn and process information and carry out skills from the simple to the complex.)

Is intelligence measured by a large brain-to-body ratio?

This theory has been debunked as well, it may work when comparing humans to elephants, but it turns out that our brain-to-body ration is almost the same as that found in mice (our brain accounts for about 2% of our total body mass).

Can brains change in size?

Yes, it appears they can. During the course of evolution brains can get larger, or smaller, or disappear altogether — as may be the case with the sea sponges. The human brain has shrunk by approximately 10% in the last 10,000 to 20,000 years.

It is thought that, in certain animals, the brain can grow and shrink during their lifetime. Research has shown that the brain of certain male song birds appears to shrink in winter and then grow again in spring. It grows when it is time to remember what songs to sing to attract a female, mark territory or recognise the call of other birds.

The brain uses about one fifth of a human’s energy supply.
The brain uses about one fifth of a human’s energy supply.

Well, the brain uses a huge amount of energy; in humans it uses about one fifth of all the body’s energy supply. Maybe human brains have become more efficient and have reduced in size while still performing the same tasks; it is possible this reduction also reduced the brains energy usage too.

The sea sponge has evolved to perform all that it needs without the need for a brain. And the song birds shrink the part of the brain responsible for song memory and recognition at a time when food, and thereby energy, is scarce.

Naomi is a science communicator and mother to three inquisitive children. She can be found at If your child has a question email

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