Rapid propagation of action potentials along myelinated axons depends on the high-density accumulation of voltage-gated sodium channels at regularly spaced interruptions in the myelin known as the nodes of Ranvier. These nodal channels are separated by a specialized axoglial junction formed between the axon and myelinating glia from potassium channels that are concealed beneath the myelin sheath. Each of these domains contains a unique set of ion channels, cell adhesion that mediate axon-glial contact and cytoskeletal adapter proteins. This organization, which depends on the presence of myelinating glial cells, is essential for the proper movement of the nerve impulses and its disruption results in the pathophysiological changes often seen in demyelinating human disorders. These lectures will describe the composition of the different membrane domains present along myelinated axons and will discuss our current knowledge of the mechanisms by which Schwann cells organize the membrane of the axons they ensheath.
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