Myelin

The faster your reaction the more likely you are to survive an attack. This speed is a necessity for any animal. In order to increase our reactions we have to be able to speed up our neuron impulses.

We can do this in two ways, either increasing the diameter of the neuron or insulating it.

The giant squid has evolved to have one of the largest neurons in the world. This neuron measures over 1mm in diameter.  

Humans have evolved insulation for their neurons. This is called Myelin. Observe the animation to the right.

The schwann cell is the small green ball. It wraps the axon in layer upon layer of a plasma membrane (blue line). This creates a fatty layer layer around the axon, as the membrane is mainly phospholipids.

The Myelin sheath is roughly 1mm in length. In between these, are small un myleinated regions called nodes of Ranvier (Seen in the diagram to the left).

The action potential will jump from node to node, this is known as Saltatory conduction.