Extracellular potential field generated by activated short muscle fibres
Dimitrov, G.V.; Dimitrova, N.A.
Agressologie 19(3): 176-186
1978
ISSN/ISBN: 0002-1148 PMID: 736217 Document Number: 126752
A mathematical model is used to study the specificities of an extracellular potential field generated in a volume conductor on activation of comparatively short muscle fibers. At relatively large radial distances the extracellular potentials recorded above the fibers have a biphasic negative-positive wave form, beyond them, biphasic positive-negative wave form, and the transition from one form to the other does not coincide with the end of the fibers. Around the ends of the muscle fibers 2 areas exist and in each point of all of them the maximum of negative phase occurs almost simultaneously, irrespective of the differences in the axial distances from these points to the motor endplate, which complicates the determination of the muscle fiber ends and creates an erroneous notion of higher propagation velocity of the excitation along the fibers. Beyond the end of the muscle fibers the amplitude of the positive phase depends nonmonotonously and the amplitude of the negative phase depends practically monotonously on the length of the depolarized zone. Increasing the degree of asymmetry of the intracellular potential, amplitude of the positive phase of the potential recorded beyond the muscle fiber ends increases, while the amplitude of the negative phase decreases. In an anisotropic volume conductor the potentials recorded beyond the end of the fiber but on its axis are as many times greater as the degree of anisotropy of the volume conductor. At greater radial distances the shape of the bipolarly recorded potentials from short muscle fibers, irrespective of the orientation of the electrode, coincides approximately with the shape of monopolarly recorded potentials. The changes in amplitude of the extracellular potentials from separate MU in human opponens pollicis muscle as a result of hypoxia are not due to the small length of the muscle fibers.