Schwann cells are a type of glial cells which wraps themselves around myelinated and non-myelinated axons to keep them alive, nourishing and protecting them. In myelinated axons, Schwann cells form the myelin sheath. This fatty sheath is not continuous. Individual myelinating Schwann cells cover about 100 micrometers of an axon. As a result, there is a string of Schwann cells along the length of the axon, much like a string of sausages. The gaps or space between adjacent Schwann cells are known as the nodes of Ranvier. Non-myelinating Schwann cells are involved in maintenance of axons and are crucial for neuronal survival.