The axons of many neurons are wrapped in a myelin sheat, which is composed of the membranes of intersticial cells and is wrapped around the axons to form several concentric layers. The myelin sheath is broken at various points by the nodes of Ranvier, so that in cross section it looks like a string of sausages. The myelin protects the axon, and prevents interference between axons as they pass along in bundles, sometimes thousands at time.