Myelin sheath

The myelin sheath ensures an increased rate of action potential propagation. In peripheral nerves the myelin sheath is formed from Schwann cell (specialised glial cells) and acts as an insulating layer to the axonal membrane in preventing current from leaking across it.

Reference: B Alberts, A Johnson, J Lewis, M Raff, K Roberts, P Walter, 2008, Molecular Biology of the Cell 5th Edition, New York : Garland Science (P678)