Theoretical analysis of mechanisms of nerve impulse conduction along myelinated fiber after a functional change in the properties of individual nodes

It is shown in a mathematical model of a myelinated nerve fiber that the development of a local response in an inexcitable node plays an important role in the mechanism of the "jumping" of an action potential (AP) across the inexcitable node. In the absence of such a response (for example, in the case of a 1000-fold decrease in the maximum sodium permeability,_Na) in fibers with normal relations between the length of the internodal segment (L) and its diameter (D) (L/D>100), the conduction is blocked. It is possible only in fibers with relatively short internodal segments (L/D<90). With a decrease in the_Na in several nodes, the transmission of excitation from the first to the second altered node is of critical importance for propagation of the impulse. The conduction of an AP becomes decremental if in each of the altered nodes the AP acquires a gradual character, for example, in the case of acceleration of sodium inactivation through the rate constant _h.A. V. Vishnevskii Institute of Surgery, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 316–324, May–June, 1971.