FIGURE 1.

Oligodendrocytes regulate axonal structure, conduction and support their survival. Schematic of an axon myelinated by an oligodendrocyte and an unmyelinated axon. Myelin permits saltatory conductance where action potentials are generated at the nodes of Ranvier. The high membrane resistance and low capacitance generated by the myelin sheath promotes rapid current flow along the myelinated section of the axon to the next node, greatly increasing conduction velocities relative to unmyelinated axons. Oligodendrocytes contact axons at the paranode (via NF155-Caspr/Contactin1) and are crucial for the organization, clustering and maintenance of sodium channels (primarily Nav1.6) at the nodes, as well as Kv1 potassium channels at the juxtaparanodes. In contrast, unmyelinated axons have potassium and sodium (primarily Nav1.2 channels) channels dispersed along the axon and are not confined to discrete excitatory clusters. Oligodendrocytes secrete exosomes that can support neuronal health and buffer potassium via the expression of Kir4.1. Oligodendrocytes provide glycolysis byproducts via monocarboxylate transporters (MCTs), which enter the Krebs cycle and are critical to support axonal metabolism.