The passage of action potentials along a myelinated axon

• Myelin acts as an electrical insulator of the axon
• Myelin physically blocks the leak of ions from the cytoplasm to the outside of the cell through leak channel proteins
• This maintenance of local current strength by myelin allows currents to flow for a longer distance before weakening
• A new action potential needs to be generated when the local current weakens
• Nodes of Ranvier are widely spaced along the axon
• Nodes of Ranvier need to be unmyelinated for the necessary exchange of ions to occur between the neurone and surrounding fluid
• Saltatory conduction -

  • In myelinated axons, depolarisation only occurs at the nodes of Ranvier and so the nerve impulse essentially jumps from node to node.
  • This is known as saltatory conduction.
  • It is much faster than conduction in non-myelinated axons.
• The transport proteins for controlling membrane potential in neurones can be concentrated at the nodes of Ranvier in myelinated neurones, since this is where action potentials are generated. This makes saltatory conduction more energy efficient, since the sodium ion-potassium ion pumps can also be localised at the nodes.