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The nervous system


Neurones are nerve cells. They carry information as tiny electrical signals. There are three different types of neurones, each with a slightly different function.

  1. Sensory neurones carry signals from receptorsreceptors: organs which recognize and respond to stimuli to the spinal cord and brain.
  2. Relay neurones carry messages from one part of the CNSCNS: Central Nervous System (brain and spinal cord). to another.
  3. Motor neurones carry signals from the CNSCNS: Central Nervous System (brain and spinal cord). to effectors.

The diagram below shows a typical neurone - in this case, a motor neurone. It has tiny branches at each end and a long fibre carries the signals.

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


Where two neurones meet, there is a tiny gap called a synapse. Signals cross this gap using chemicals. One neurone releases the chemical into the gap. The chemical diffuses across the gap and makes the next neurone transmit an electrical signal.

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