The brain is made from nerve cells. These cells can communicate with each other.

The way nerve cells communicate is through tiny currents of electricity which are called electrical messages or signals.

Most of the nerve cells outside the brain are very long thin fibres. They join together to form white cords called nerves which run to most parts of the body.

A nerve cell can send its electrical message all the way along its fibre. The longest fibre runs from the end of your big toe to the base of your spine. When the message reaches the end of the fibre a chemical is made which starts the message again in the next nerve cell and the message travels on.

Messages are started in two places in the body. They are started in the sense organs and they are started in the brain. The sense organs are the eye, ear, nose, tongue and skin. Each organ contains special cells called receptor cells which set off messages to the brain. For example when a smell enters the nose, receptor cells in the nose send messages to the brain telling it that a smell has entered the nose. In a similar way if you sit on a sharp object receptor cells in your skin will send messages to the brain which the brain may sense as pain.

The brain sends out messages when it is has thought of something for the body to do. For example you may think "I have spent too long on the Internet so I will go for a walk". The brain then sends out messages to your muscles to move your hands to switch off the computer then sends message to the muscles in your legs to make you stand and walk away.

Nerve cells can only send a message in one direction along a fibre. This means that if the eye sent a message to the brain that said "There is dust in the eye so it needs to blink" the brain could not send a message back down the same nerve fibre to make the eye blink. It has to send it down a second fibre which is connected to the muscles which makes the eye blink. This arrangement of fibres is found throughout the nervous system. There are sensory nerve fibres which take messages to the brain from the sense organs and there are fibres which carry messages from the brain to the muscles. These fibres usually cause some movement of the body and are known as motor nerve fibres.