What is the purpose of myelin on a neurone?

The myelin on peripheral neurones come in the form of schwann cells. These schwann cells are essentially coils of fat that sit around the neurone and insulate it, this has two fundamental purposes.
1 - The first purpose is to act purely as an insulator, much like an insulator on a wire. It keeps the electrical flow moving in the right direction. 2 - The second is to increase the conduction speed of the neurone, this occurs because there are gaps between the schwann cells called NODES OF RANVIER. These nodes allow a process called Saltatory conduction to take place, which is in essence the jumping of an action potential (nerve electrical pulse) from one gap to another increasing their speed.