ACTION-POTENTIALS AND IONIC CURRENTS THROUGH PARANODALLY DEMYELINATEDHUMAN MOTOR-NERVE FIBERS - COMPUTER-SIMULATIONS

The relationship between the changes in the passive paranodal properti es of the myelinated human motor nerve fibres and the conduction abnor malities obtained is examined on the basis of a double-cable model. Si mulated systematic demyelination (all paranodal regions uniformly affe cted) and focal demyelination (paranodal regions at each end of a sing le internode affected) of the fibres are defined as a reduction of the paranodal seal resistance. By increasing the degree of demyelination, the kinetics of the action potentials and ionic currents in different segments of the fibres are explored. The altered paranodal seal resis tance is found to be a factor impeding the invasion of the demyelinate d regions by an action potential. We established that the conduction a long the most severely demyelinated fibres (i.e. in the case of system atically demyelinated fibres) is more affected than along the focally demyelinated fibres.