the brain quick facts
- An adult brain weighs about 3 pounds (1.4 kg); a newborn’s weighs about 1 pound.
- The brain has about 86 billion neurons and about as many glial cells.
- The right half of the brain mostly controls the left side of the body.
- The pituitary gland is about the size of a pea.
- The cortex, or grey matter, is only about as thick as two or three stacked coins.
What is the brain?
Your brain is the control centre of your body. It lets you think, learn, remember and feel. It controls how you move, and it makes sense of everything you see, hear, smell, taste and touch.
It also runs lots of jobs you never have to think about, such as breathing, keeping your heart beating and digesting your food.
The US National Institute of Neurological Disorders and Stroke calls the brain the most complex part of the human body. It is the organ that makes you, you.
Where is the brain?
Your brain is inside your head, protected by your skull. Under the skull, three thin layers of tissue called the meninges wrap around the brain.
Between those layers is a clear liquid called cerebrospinal fluid. It cushions the brain, so it does not bump against the skull when you move.
The brain connects to the rest of your body through the spinal cord, a long bundle of nerves that runs down inside your backbone. Together, the brain, spinal cord and nerves make up your nervous system.
How big is the brain?
An adult’s brain weighs about 3 pounds, or roughly 1.4 kg. That is about the weight of a large bag of sugar.
A newborn baby’s brain weighs about 1 pound. It grows fast, to about 2 pounds during childhood, before reaching its adult size.
For an adult weighing about 70 kg, a 1.4 kg brain is only about 2% of their weight. Yet the brain is one of the busiest organs in the body. It never switches off completely, not even when you are fast asleep.
The three main parts
The brain has three main parts: the cerebrum, the cerebellum and the brainstem.
The cerebrum is the biggest part, the wrinkly part you see in most pictures of the brain. It is the thinking part. It holds your memories and lets you plan, imagine, read, recognise your friends and play games. It also controls the muscles you move on purpose.
The cerebellum sits at the back of the brain, below the cerebrum. It controls balance, posture and coordination. When you ride a bike, play the piano or hit a tennis ball, your cerebellum is hard at work.
The brainstem sits underneath and connects the brain to the spinal cord. It runs the things your body needs to stay alive, like breathing, your heart rate and digesting food, without you having to think about them.
| Part | Where it is | What it does |
|---|---|---|
| Cerebrum | the large, wrinkly top part | thinking, memory, planning, senses and voluntary movement |
| Cerebellum | at the back, below the cerebrum | balance, posture and coordination |
| Brainstem | underneath, joined to the spinal cord | breathing, heart rate and other automatic jobs |
Two halves
The cerebrum is split into two halves, called hemispheres, by a deep groove down the middle. The two halves talk to each other through a thick bundle of nerve fibres called the corpus callosum.
The halves look almost the same, but they are a little different. The ability to form words seems to sit mostly in the left half. The right half seems to handle many kinds of abstract thinking.
Here is a strange fact. Nearly all the signals between the brain and the body cross over on the way. So the right half of your brain mostly controls the left side of your body, and the left half controls the right side. Scientists still don’t know exactly why.
Brain parts and wiring
- The spinal cord — the long bundle of nerves inside your backbone
- The corpus callosum — the thick bundle of nerve fibres joining the two halves
- Hemispheres — the two halves the cerebrum is split into
- The brainstem — the part that runs breathing, heart rate and digestion
- The cerebrum — the large wrinkly top part that does the thinking
- Neurons — the cells that carry messages around the brain
The four lobes
Each half of the cerebrum is divided into four areas, called lobes. Each lobe has its own special jobs.
The frontal lobes are just behind your forehead. They help you plan, imagine the future and think things through. At the back of each frontal lobe is the motor cortex, which controls movements such as moving your arm or kicking a ball.
The parietal lobes sit behind the frontal lobes. They take in information about touch, temperature, taste and movement from the rest of your body. They also help with reading and arithmetic.
The occipital lobes are at the very back of your head. They handle what you see. They take the images from your eyes and link them to pictures stored in your memory.
The temporal lobes are at the sides, near your ears. They receive information from your ears, including music, and they play a big part in making and finding memories and in language.
Why the brain is wrinkly
The outer layer of the cerebrum is called the cortex, from the Latin word for bark. It is only about as thick as a stack of two or three coins, but most of the brain’s information processing happens here.
The cortex is grey, which is why people call it grey matter. Underneath is white matter, made of nerve fibres that carry signals around the brain and down into the body.
The brain’s wrinkles and folds let far more cortex fit inside your skull. More cortex means more room for thinking.
A message through a neuron
- First Short branches called dendrites receive a message from another neuron.
- Then The message passes into the main body of the neuron.
- Next It travels along a long wire-like part called the axon.
- Faster here A fatty coating called myelin helps the signal travel faster and further.
- At the end The signal reaches a tiny gap called a synapse.
- Across the gap Chemicals called neurotransmitters carry the message to the next neuron.
Deep inside the brain
Deep inside, hidden from view, are some small but very important parts.
The hypothalamus is about the size of a pearl. It works like your body’s thermostat. If you get too hot, it tells your body to sweat. It helps wake you up in the morning, and it has a lot to do with your feelings.
The pituitary gland is only about the size of a pea. It makes hormones, chemical messengers that travel in your blood and tell parts of your body what to do, including how to grow.
The hippocampus works a bit like a librarian for memories. It sends memories off to be stored in the right places, and helps find them again when you need them.
What each lobe does
- The frontal lobes — planning, imagining the future and thinking things through
- The parietal lobes — touch, temperature, taste and movement, plus reading and arithmetic
- The occipital lobes — making sense of what you see
- The temporal lobes — hearing, music, language and finding memories
- The hypothalamus — working like your body's thermostat
- The hippocampus — filing memories away and helping you find them again
Brain cells
The brain is made of billions of cells. The ones that carry messages are called neurons, or nerve cells. The human brain has about 86 billion of them, and about as many other cells, called glial cells, that look after them.
A neuron has a main body, short branches called dendrites that receive messages, and a long wire-like part called an axon that sends them on. Many axons are wrapped in a fatty coating called myelin, which helps signals travel faster and further. Some axons are very short, reaching a cell less than a hair’s width away. Others are very long, carrying messages from the brain all the way down the spinal cord.
Neurons pass messages to each other across tiny gaps called synapses, using chemicals called neurotransmitters. Every thought, feeling, memory and movement you make depends on these messages.
Looking after your brain
Your brain works hard all day and all night, so it is worth looking after.
Wear a helmet when you ride a bike, scooter or skateboard. It protects your brain if you fall.
Eat healthy food. It contains vitamins and minerals that your nervous system needs.
Play and exercise. Being active is good for your whole body, including your brain, and your heart, which pumps blood to it.
Get enough sleep. Your brain needs rest to work well the next day.
Keep learning. Every time you learn something new, like a word, a song or a sport, your neurons make new connections. A busy, curious brain is a healthy brain.
Three things people get wrong
The brain does not have 100 billion neurons. The best count is about 86 billion, with about as many glial cells beside them.
Each side of the brain does not control the same side of the body. The right half mostly controls the left side of the body, and the left half the right side.
Grey matter is not the whole brain. It is the thin outer cortex. Much of the brain underneath is white matter, made of nerve fibres.
Did you know? Nearly all the signals between your brain and your body cross over on the way, so the right half of your brain mostly controls the left side of your body.
Your brain: fact or myth?
- Your brain switches off completely while you are fast asleep.
- The brain's folds and wrinkles let more of its outer layer fit inside the skull.
- An adult brain makes up about a fifth of a person's body weight.
- Glial cells look after the neurons around them.
- All axons are about the same length.
- Learning something new makes your neurons build new connections.
Try it
Stand on one foot with your eyes open, then try again with your eyes closed. It is harder, because your cerebellum uses information from your eyes to help you balance.
Knowledge check
Which part of the brain controls balance?
Show answer
The cerebellum, at the back of the brain below the cerebrum.
What protects the brain?
Show answer
The skull, three layers of tissue called the meninges, and a cushioning liquid called cerebrospinal fluid.
Frequently asked questions
How much does the human brain weigh?
An adult human brain weighs about 3 pounds, or roughly 1.4 kg. A newborn baby’s brain weighs about 1 pound and grows to about 2 pounds during childhood.
What are the three main parts of the brain?
The three main parts of the brain are the cerebrum, which handles thinking and memory, the cerebellum, which controls balance, and the brainstem, which runs breathing and heartbeat.
How many neurons are in the brain?
The human brain has about 86 billion neurons, or nerve cells, and about the same number of glial cells that support and protect them.
What are the four lobes of the brain?
Each half of the cerebrum has four lobes: the frontal lobe for planning, the parietal lobe for touch and body sense, the occipital lobe for sight, and the temporal lobe for hearing and memory.
Why is the brain wrinkly?
The brain’s folds let much more of its outer layer, the cortex, fit inside the skull. More cortex means more room for processing information.
How can kids keep their brain healthy?
Kids can keep their brain healthy by wearing a helmet for cycling and skating, eating healthy food, playing and exercising, and getting enough sleep.
Sources
- US National Institute of Neurological Disorders and Stroke: brain basics — the parts of the brain, the hemispheres, the lobes, the cortex, the inner brain and neurons
- Cleveland Clinic: brain — brain weight, the number of neurons and glial cells, grey and white matter, and how the brain is protected
- KidsHealth (Nemours): your brain and nervous system — the pituitary gland, the hypothalamus, the brain stem and keeping your brain healthy
Brain Facts Final Challenge
- About how much does an adult human brain weigh?
- About how much does a newborn baby's brain weigh?
- How many neurons does the human brain have?
- Which half of the brain mostly controls the left side of the body?
- Where is the motor cortex?
- What is grey matter?
- Which part of the brain is about the size of a pea?
- What do you call the tiny gaps that neurons pass messages across?
- Which of these makes up your nervous system?
- Which half of the brain seems to do most of the work of forming words?
- Why does the guide say to wear a helmet when you cycle or skate?
