Ultrastructurally, the Schwann cell is unique and distinct from the oligodendrocyte. Each Schwann cell is surrounded by a basal lamina made up of a mucopolysaccharide approximately 20 to 30 nm thick that does not extend into the mesaxon (Fig. 1-19). The basal laminae of adjacent myelinating Schwann cells at the nodes of Ranvier are continuous, and Schwann cell processes interdigitate so that the PNS myelinated axon is never in direct contact with the extracellular space. These nodal Schwann cell fingers display intimate relationships with the axolemma (Figs. 1-20 and 1-21), suggesting that the entire nodal complex might serve as an electrogenic pump for the recycling of ions [10]. A similar arrangement between the nodal axon and the fingers of astroglial cells is seen in the CNS. The Schwann cells of nonmyelinated PNS fibers overlap, and there are no nodes of Ranvier.