Effect of External Tissue Resistivity on Threshold Level of Myelinated Nerve Fiber

摘要

The rise of the threshold of electric current stimulation to generate compound action potential of nerve conduction study is considered to have a relationship to malfunctions of the nerve. The effect of the decrease of the resistivity of the external tissue and the thickness of myelin sheaths was investigated hy computer simulation. A myelinated human nerve fiber dipped in the homogeneous conductor was stimulated with a monopolar cathode located outside the axon. The rise of the threshold by demyelination was found to be comparable to the effect of the decrease of the resistivity of the external tissue by a few Ωm when the external resistivity is about 10 Ωm. Actually the reduction of the thickness of the myelin sheaths also reduces the resistivity of the external tissue. Therefore, the contribution of both effects in the case of demyelination was estimated. As a result, the contributions of each effect were antagonized. As one of the causes of the rise of the threshold of nerve activation, the decrease of the resistivity of the external tissue is considerable.