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Science

Your senses and nervous system

The nervous system

The main parts of the nervous system are the central nervous system - the CNS - the brain and spinal cord - and the peripheral nervous system. Nerve impulses are mainly electrical and carried in nerve cells, or neurones.

Neurones

The diagram shows the main parts of a motor neurone - which carries nerve impulses to effectors such as muscles.

a neurone has a 'head' at one end where the nucleus, cytoplasm, cell membrane and dendrite are. The axon is tail-like, with nerve endings at the end which look like branches.

A motor neurone

The nerve impulse is carried in the axon.

Neurones - higher

The sheath acts as an insulator - rather like the plastic coating of an electrical wire. Neurones are adapted to their function by being long, so that they communicate with distant parts of the body. They also have branched endings called dendrites. These connect with many other neurones.

The gap between two neurones is called a synapse. The nerve impulse passes across this gap through chemicals that diffuse across the gap. The electrical signal travels along an axon and triggers the release of chemical transmitters from the nerve ending of the first neurone. These diffuse across the gap and make the second neurone re-transmit the electrical signal. The animation shows how this works:

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