In some neurones, cells called Schwann cells wrap themselves around the axon all along its length. The Schwann cell spirals around, enclosing the axon in many layers of its plasma membrane. The enclosing sheath is call the Myelin sheath. It is mainly made of lipids together with some proteins. There are small, uncovered gaps along the axons where there are spaces in the Schwann cells (and therefore in the Myeline sheath). These are known as nodes of Ranvier. This of the myeline sheath encasing the axon a bit like a swiss roll.