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Propagation of the Action Potential
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
After having considered the generation of the action potential (AP) in the preceding chapter, the present chapter is concerned with the propagation of the AP. Propagation along an unmyelinated axon is considered first, qualitatively to begin with, and then quantitatively in terms of RC cable theory. The cable equation is derived in detail and solved for a semi-infinite cable subjected to different types of stimuli that illustrate some important features of cable behavior, including the variation of the speed of conduction of the AP as the square root of axon diameter.
Chronic Pain Following Electrical Injury
Published in Gary W. Jay, Practical Guide to Chronic Pain Syndromes, 2016
Elongated cells such as nerves and skeletal muscles for which the long axis is parallel to the direction of current flow are most vulnerable to membrane damage by electroporation (29). For example, electroporation of skeletal muscle tissue should be expected when more than 0.5 A of electrical current is passed through an extremity. Also, an electric field of 200 V/m in the direction of a 1-cm-long skeletal muscle cell should be sufficient to cause electroporation (24). Classical cable theory predicts that an externally imposed electric field will induce the greatest membrane potential in nerve cells with larger space constants and shorter charging times. It follows that large myelinated nerve cells, which have greater conduction velocities, are the most susceptible to electrical injury due to the higher probability of electroporation. Since peripheral nerves consist of nerve fibers with various diameters and degrees of myelination, it is important to recognize that the pattern of electrical injury is likely to be nonhomogenous, with greater damage to faster-conducting than to the slower-conducting fibers (2, 5, 19).
The use of passive cable theory to increase the threshold of nociceptors in people with chronic pain
Published in Physical Therapy Reviews, 2021
Ayman A. Mohamed, Motaz Alawna
Passive cable theory helps in increasing inward current conductance (the negative slope conductance). The negative slope conductance region occurs when the electrical current is triggered by depolarization which causes positive feedback between the stimulation and the amplitude of the current throughout a reformative mechanism. The stimulation phase of the voltage-gated sodium and calcium currents are considered examples of areas of negative slope conductance. The final result of the negative slope conductance is a net rise in the total membrane impedance [89,93]. Thus, increasing this negative cable conductance can help in increasing the threshold of the neuronal membrane and decrease its sensitivity. The passive cable theory in nerve cell is illustrated in Figure 1.