Got the need for speed?

The speed of nerve impulses varies enormously in different types of neuron. The fastest travel at about 250 mph, faster than a Formula 1 racing car. For the impulse to travel quickly, the axon needs to be thick and well insulated. This uses a lot of space and energy, however, and is found only in neurons that need to transfer information urgently. For example, if you burn your fingers it is important that your brain gets the message to withdraw your hand very quickly.

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Your fastest nerve impulses travel faster than a Formula One racing car!

How do nerve impulses code information?

Nerve impulses are a way of coding information, in a similar way to FM radio, allowing information to be transmitted both quickly and accurately. Each impulse is the same size so it is the frequency that carries information about the intensity of the signal. For example, as you turn up the dimmer switch on your bedroom light, the size of the nerve impulses from your eye stays the same but the rate at which they are generated increases.

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The giant axons of the squid were crucial in helping scientists understand nerve impulses.

What is myelin?

Neurons that need to transmit electrical signals quickly are sheathed by a fatty substance called myelin. Myelin acts as an electrical insulator, and signals travel 20 times faster when it is present. In the disease multiple sclerosis, the myelin around the axons of some nerves gradually breaks down, so that the nerves can no longer efficiently carry electric signals between the brain and body.

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Electron micrograph of nerve fibres, some surrounded by dark myelin sheaths.

 

Principal Funder:

Wellcome trust

Major Sponsors:

GlaxoSmithKline life technologies