3. The structure and function of neurone

• Types of neurons


  • Motor
  • Sensory
  • Relay neurones
• Neurone

  Nerve cells that process and transmit messages through electrical and chemical signals
• Function of sensory neurone

  Carry messages from the PNS to the CNS
• Structure of sensory neurone

  • They have long dendrites and short axons
• Function of relay neurone

  Connect the sensor neurone to motor neurone and other relay neurones
• Structure of relay neurone

  • They have short dendrites and short axons
• Function of motor neurone

  Connects CNS to effectors such as muscles and glands
• Structure of motor neurone

  • They have short dendrites and short axons
• Neurones


  • Vary in size - a meter to a millimetre long
• Cell body or soma


  Includes nucleus - contains genetic material
• Dendrites


  Protrude from the cell body - carry nerve impulses from neighbouring neurones towards the cell body
• Axon


  Carries impulses down the length of the neurone away from the cell body
• Axon covered in myelin sheath

  Fatty layer which covers and protects the axon and speeds up chemical transmission
• If myelin sheath was continuous, it would slow down electrical impulses
• Gaps between myelin sheath - 'nodes of Ranvier'


  Speed up transmission by forcing it to 'jump' across gaps on the axon
• Terminal buttons


  End of the axon - communicate with the next neurone across the synapse
• Electric transmission


  1. Neurone resting - inside more negatively charged compared to the outside

  2. When neurone activated by stimuli, inside becomes more positively charged causing action potential to occur

  3. This creates an electrical impulse that travels down the axon and towards the end of a neurone