Myelination

• An unmyelinated neuron, the speed of conduction is very slow
• Myelin

  Insulates the axon membrane and increases the speed at which action potential can travel along the neuron
• In sections of the axon that are surrounded by a myelin sheath, depolarization (and action potentials) cannot occur, as the myelin sheath stops the diffusion of sodium and potassium ions
• Nodes of Ranvier


  Small uninsulated sections of the axon where depolarization can occur
• Local circuit of current that trigger depolarization in the next section of axon membrane exist between nodes of Ranvier
• Saltatory conduction

  Action potential ‘jumps’ from one node to the next
• Saltatory conduction allows impulses to travel much faster (up to 50x) than unmyelinated axon of the same diameter
• Diameter 

  • The speed of conduction of an impulse along neurons with thicker axons is greater than along those w thinner 
  • Thicker axons have an axon membrane w a greater surface area over which diffusion of ions can occur 
  • Increases rate of diffusion of sodium ions and potassium ions, which in turn increase the rate at which depolarization and action potentials can occur