Prerequisites for conduction in demyelinated fibers.

Data are herein reviewed which show that there are structural differences between nodal and internodal membrane in normal myelinated fibers. It appears likely that in most normal myelinated fibers, ionic channel densities in the internodal axon membrane are lower than those at the nodes of Ranvier. Conduction through demyelinated fibers may require structural reorganization, for example, redistribution or production of new channels, in the internodal membrane. Impedance mismatch may also block conduction at sites of demyelination. Reduction in internode distance proximal to the site of demyelination provides one solution to the problem of impedance matching.