Saltatory circulation

Action potential in myelinated neurones

• ion channels are not present in the myelinated parts of neurones

• only found in the Nodes of Ranvier

  • gaps between the schwann cells in myelinated neurones

  • 1-3mm apart

Saltatory conduction

1. as charge spreads down an axon, myelination (via schwann cells) prevents ions from leaking out across the plasma membrane

2. charge spreads unimpeded until it reaches an unmyelinated section of the axon (Node of Ranvier) which is packed with Na+ channels

3. in this way, electrical signals continue to jump (like saltation transportation) down the axon much faster than they can move down an unmyelinated cell

Saltatory conduction cont.

• sodium ion channels open and sodium ions enter at one node causing depolarisation of the neurone

• the sodium ions diffuse along the the neurone to the next node

• depolarisation then occurs here and sodium ion channels at this node open and sodium ions then enter at the node

• the impulse jumps from node to node

Saltatory conduction is faster

• diffusion of sodium ions to the next Node of Ranvier is faster than opening and closing many voltage gated ion channels

  • localised circuits are longer

• less ATP in needed for functioning of fewer Na/K pumps