• Information is sent through the nervous system as?nerve impulses?– electrical signals that pass along nerve cells known as?neurones
• A bundle of neurones is known as a nerve
• Neurones?coordinate?the activities of?sensory receptors?(eg. those in the eye),?decision-making centres?in the central nervous system, and?effectors?such as muscles and glands
• Neurones have a?long fibre?known as an?axon
• The axon of some neurones is?insulated?by a?fatty sheath?with small uninsulated sections along its length (called?nodes of Ranvier)
  • The sheath is made of?myelin, a substance made by specialised cells known as?Schwann cells
  • Myelin is made when Schwann cells wrap themselves around the axon along its length

   

• The presence of Schwann cells means that the electrical impulse does not travel down the whole axon, but jumps from one node to the next
  • The 'jumping' of the electrical impulse between nodes of Ranvier is called?saltatory conduction
  • This?speeds up the conduction?of the impulse and its transfer from one cell to another

   

• Neurone?cell bodies?contain many extensions called?dendrites
  • This means they can?connect?to many other?neurones?and receive?impulses?from them, forming a?network?for easy?communication

   

An example of a neurone?

• There are?three main types?of neurone:?sensory, relay and motor
  • Sensory?neurones carry impulses from?receptors?to the?CNS?(brain or spinal cord)
  • Relay?(intermediate) neurones are found entirely within the CNS and?connect?sensory?and?motor?neurones
  • Motor?neurones carry impulses from the?CNS?to?effectors?(muscles or glands)

   

• Each type of neurone has a?slightly different structure
• Motor neurones?have:
  • A large cell body at one end, that lies within the spinal cord or brain
  • A nucleus that is always in its cell body
  • Many highly-branched dendrites extending from the cell body, providing a large surface area for the axon terminals of other neurones

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