Neurones

• Neurones

  Specialised cells of the nervous system which carry electrical impulses around the body
• Nerve


  A bundle of neurones
• Features found in all types of neurone

  • Long fibre known as an axon
  • Cell body that contains the nucleus and other cellular structures
  • Axon terminal at the end of the axon containing many nerve endings
• Myelinated neurones

  • Axon insulated by a myelin sheath with small uninsulated sections along its length (called nodes of Ranvier)
  • Myelin sheath formed by Schwann cells wrapping around the axon
  • Electrical impulses jump from one node to the next
• Non-myelinated neurones

  • Axon is uninsulated
  • Impulse travels more slowly as it moves through the entire length of the axon
• Main types of neurone

  • Sensory
  • Relay (intermediate)
  • Motor
• Sensory neurones


  Carry impulses from receptors to the CNS (brain or spinal cord)
• Relay (intermediate) neurones


  Found entirely within the CNS and connect sensory and motor neurones
• Motor neurones


  Carry impulses from the CNS to effectors (muscles or glands)
• Sensory neurone structure


  • Cell body branches off in the middle of the cell
  • Single long dendron that carries impulses to the cell body
  • Single long axon that carries impulses away from the cell body
• Relay neurone structure

  • Short, but highly branched, axons and dendrites
• Motor neurone structure

  • Large cell body at one end that lies within the spinal cord or brain
  • Nucleus always in its cell body
  • Many highly-branched dendrites extending from the cell body