The nervous system is the body’s control centre and messaging network. It is made of the brain, the spinal cord and nerves that reach all over the body. Messages travel along nerve cells called neurons as tiny electrical pulses, at up to about 190 km/h. The brain has about 86 billion neurons.
the nervous system quick facts
- The nervous system is made of the brain, spinal cord and nerves.
- An adult brain weighs about 1.4 kg (3 pounds).
- The brain has about 86 billion neurons.
- There are 31 pairs of spinal nerves and 12 pairs of cranial nerves.
- Nerve signals can travel at up to about 190 km/h (120 mph).
What is the nervous system?
Your nervous system is your body’s control centre and messaging network. KidsHealth says it is made of your brain, your spinal cord and a huge network of nerves that reach all over your body.
Every time you feel something, think something or move, your nervous system is at work. It carries messages between your brain and every part of your body, faster than you can blink.
It also does many jobs without you even noticing, like keeping your heart beating and your lungs breathing, day and night.
| Nervous system at a glance | |
|---|---|
| Main parts | brain, spinal cord and nerves |
| Adult brain weight | about 1.4 kg (3 pounds) |
| Neurons in the brain | about 86 billion |
| Pairs of spinal nerves | 31 |
| Pairs of cranial nerves | 12 |
| Top nerve signal speed | up to about 190 km/h (120 mph) |
Two main parts
KidsHealth and Cleveland Clinic say the nervous system has two main parts.
The central nervous system: your brain and your spinal cord. This is the main control centre.
The peripheral nervous system: all the nerves outside the brain and spinal cord. They carry messages to and from the rest of your body.
Cleveland Clinic says the nervous system can also be split up by the jobs it does. One part handles the movements you choose to make, like kicking a ball. Another part runs things automatically, like your heartbeat and blood pressure.
The brain
Your brain is the boss of your body. Cleveland Clinic says an adult brain weighs about 1.4 kg (3 pounds). A newborn baby’s brain weighs about 0.45 kg (1 pound), and it grows to about twice that during childhood.
The Queensland Brain Institute says that at birth, your brain is about a third of its adult size, and at first it grows by about 1% every day.
Cleveland Clinic says the brain has three main parts: the cerebrum, the cerebellum and the brainstem. Find out even more in our brain facts for kids.
The cerebrum
The cerebrum is the biggest part of your brain. KidsHealth says it controls the muscles you move on purpose, and handles memory, thinking, maths and speech.
It has a left half and a right half, called hemispheres. Cleveland Clinic says each half has four areas, called lobes: the frontal, parietal, temporal and occipital lobes.
The wrinkly outer layer of the brain is called the cortex. The Queensland Brain Institute says it makes up about 82% of the brain’s weight.
The cerebellum and brainstem
The cerebellum sits at the back of your brain, below the cerebrum. KidsHealth says it controls balance, movement and coordination, so it helps you ride a bike or catch a ball.
The brainstem connects your brain to your spinal cord. KidsHealth says it runs automatic jobs like breathing, digesting food and keeping your heart pumping blood. It also passes messages between the brain and the body.
Small but mighty parts
Some parts of the brain are small but very important.
The pituitary gland: KidsHealth says it is only about the size of a pea, but it releases hormones that control how you grow.
The hypothalamus: it works like your body’s thermostat, KidsHealth says. It keeps you at about 37 °C (98.6 °F), by making you sweat when you are hot or shiver when you are cold.
The amygdala: this almond-shaped part helps you handle emotions, such as fear.
The hippocampus: it is shaped like a seahorse. The Queensland Brain Institute says it can make about 700 new neurons every day.
Neurons: the messenger cells
Your nervous system is made of special cells called neurons, or nerve cells. They carry messages around your body.
There are a lot of them. Cleveland Clinic says the brain has about 86 billion neurons. That is more than ten times the number of people on Earth.
Neurons have helpers too. Cleveland Clinic says the brain has at least as many support cells, called glia, as it has neurons.
Cleveland Clinic says there are three main kinds of neurons. Sensory neurons carry information from your senses to your brain. Motor neurons carry orders from your brain to your muscles. Interneurons connect the two.
Parts of a neuron
The Queensland Brain Institute says a neuron has three main parts.
Dendrites: branches that receive messages from other neurons. They are covered in tiny bumps called spines.
The cell body: the centre of the neuron, which holds the nucleus and the cell’s DNA.
The axon: a long, thin wire that sends messages on to the next cell.
How messages travel
Neurons send messages as quick pulses of electricity, called nerve impulses. The Queensland Brain Institute says neurons do not quite touch each other. They are separated by tiny gaps called synapses.
When a message reaches the end of a neuron, it releases a chemical, called a neurotransmitter. The chemical crosses the gap and passes the message on to the next cell.
The brain is packed with connections. The Queensland Brain Institute says a single neuron can connect to other neurons through up to 40,000 synapses. A piece of brain the size of a grain of sand holds about 100,000 neurons and 1 billion synapses.
Messages travel fast. Cleveland Clinic says signals in healthy nerves can travel at up to about 190 km/h (120 mph). Nerves with a fatty coating, called myelin, carry signals fastest. A newborn baby’s nerves carry signals about half as fast as an adult’s, and reach adult speed by about age three or four.
The spinal cord
The spinal cord is like a thick cable of nerves that runs down the middle of your back, from your brain. The Queensland Brain Institute says it weighs only about 35 grams and is about 1 cm wide.
It is well protected. The Queensland Brain Institute says it is surrounded by 26 bones called vertebrae, and by three layers of protective tissue.
Nerves branch out from the spinal cord to the rest of your body. There are 31 pairs of spinal nerves: 8 in the neck, 12 in the chest, 5 in the lower back, 5 in the pelvis and 1 at the tailbone.
Nerves everywhere
Nerves reach every part of your body, from your scalp to your toes. They are part of the peripheral nervous system.
Cleveland Clinic says there are also 12 pairs of cranial nerves, which connect straight to the brain rather than to the spinal cord.
The longest cranial nerve is the vagus nerve. Cleveland Clinic says it runs from the brain all the way down to the large intestine, and helps control your heart rate, breathing and digestion.
Your senses
Your nervous system lets you see, hear, smell, taste and touch. KidsHealth says sensory neurons carry information from your eyes, ears, nose, tongue and skin to your brain.
Some cranial nerves are sense nerves. Cleveland Clinic says the olfactory nerve carries smell, the optic nerve carries sight, and another nerve carries both hearing and balance.
Reflexes
Have you ever pulled your hand away from something hot before you even knew it was hot? That was a reflex. Cleveland Clinic says a reflex is a fast, automatic movement your body makes without you having to think.
Reflexes work through a shortcut called a reflex arc. Sensors in your skin notice the heat, a sensory neuron carries the message to your spinal cord, and a motor neuron carries an order straight back to your muscles.
The Queensland Brain Institute says many reflexes are handled by the spinal cord, so they skip the thinking part of the brain. That is why they are so fast.
Cleveland Clinic says examples include the knee-jerk when a doctor taps just below your kneecap, blinking, gagging and shivering.
A growing brain
Your brain changes a lot as you grow. Cleveland Clinic says most brain development happens between birth and the teenage years, but the brain keeps developing until people are in their mid-to-late twenties.
Even grown-ups can make new neurons. The Queensland Brain Institute says this is called neurogenesis.
Keeping your nervous system healthy
You can help look after your nervous system. Cleveland Clinic says you should wear a helmet and the right safety gear for sports, eat balanced meals, avoid tobacco and have regular check-ups.
Cleveland Clinic also says that exercise, plenty of sleep, puzzles, time with friends and healthy food all help keep your brain healthy.
Three things people get wrong
Nerve messages are not slow. They can travel at up to about 190 km/h.
Your brain is not finished growing when you are a child. It keeps developing into your twenties.
Reflexes do not need thinking. Many are handled by the spinal cord.
Did you know? A piece of brain the size of a grain of sand holds about 100,000 neurons and 1 billion connections.
Try it
Test your reflexes: ask a friend to drop a ruler between your fingers and see how quickly you catch it.
Knowledge check
What are the two main parts of the nervous system?
Show answer
The central nervous system and the peripheral nervous system.
What is a reflex?
Show answer
A fast, automatic movement your body makes without you thinking.
Frequently asked questions
What is the nervous system?
The nervous system is the body’s control centre and messaging network. It is made of the brain, the spinal cord and nerves all over the body.
What does the brain do?
The brain controls thinking, memory, speech, movement, balance and automatic jobs like breathing and keeping your heart beating.
What are neurons?
Neurons are nerve cells that carry messages as tiny electrical pulses. The brain has about 86 billion of them.
How fast do nerve signals travel?
Signals in healthy nerves can travel at up to about 190 km/h (120 mph). Nerves with a fatty myelin coating are fastest.
What is a reflex?
A reflex is a fast, automatic movement, like pulling your hand away from something hot. Many reflexes are handled by the spinal cord.
How can I keep my nervous system healthy?
Wear a helmet for sports, eat balanced meals, sleep well, exercise, do puzzles, spend time with friends and avoid tobacco.
Sources
- KidsHealth: your brain and nervous system — brain parts and their jobs
- KidsHealth: brain and nervous system (for parents) — the central and peripheral nervous systems and kinds of neurons
- Cleveland Clinic: nervous system — parts, kinds of neurons, signal speed and staying healthy; its pages on the brain, cranial nerves and reflexes were also used
- Cleveland Clinic: brain — brain weight, neuron count, lobes, development and brain health
- Queensland Brain Institute: what is a neuron? — parts of a neuron, synapses and neurotransmitters; its brain-facts poster was also used
- Queensland Brain Institute: the spinal cord — size, protection, spinal nerves and reflexes
