Speed of the impulse

• What are the factors affecting the speed of an action potential?

  • Myelin sheath
  • Diameter of the axon
  • Temperature
• How does the myelin sheath affect the speed of the action potential?


  Acts as an electrical insulator, so saltatory conduction can occur
• How does the diameter of the axon affect the speed of the action potential?

  The greater the diameter of the axon, the faster the impulse
• How does temperature affect the speed of an action potential?

  The higher the temperature the faster the nerve impulse, as energy for active transport comes from respiration. Respiration is controlled by enzymes, which function better at higher temperatures
• What is the all-or-nothing principle?


  A neurone either fires completely or does not fire at all in response to a stimulus, and in order to fire it must reach a threshold value
• What is the refractory period?


  Recovery phase after a neuron has fired, during which it cannot fire again as the voltage-gated sodium ion channels are closed
• What does the refractory period ensure?

  • Action potentials are only propagated in one direction
  • Produces discrete impulses
  • Limits the number of action potentials