Schwann Cell Producing Mielin Sheath on the Nerve Axon

If the outer surface of the nerve axon is electrically isolated on most parts then the action potential travels much faster.

The isolation is produced by Schwann cells which wrap around the axon thus isolating it with their lipid cell membranes.

Here the animation shows how the Schwan cell wraps around the axon (blue cyllinder). The "unwrap" command is just for easier observation, in reality the Schwann cells do not unwrap.