Simulation of single muscle fibre action potentials
Using the volume conductor model, a single muscle fibre action potential can be expressed as a convolution of the transmembrane current and a weighting function. By simplifying the weighting function, the line source model is derived. We have developed similar expressions to compute the single muscle fibre action potential using simple models and physical considerations without any mathematical complexity. The relationship between the conduction velocity and amplitude is analysed and it is concluded that, for a given fibre, the amplitude is inversely proportional to the conduction velocity. This agrees with the experimental data reported in the literature.
The relation between amplitude and fibre diameter is studied. The amplitude increases with diameter owing to the increase in membrane current, but it is counteracted by the increase in conduction velocity. Because of the opposing effects, a point of inflection in the amplitude/diameter relationship is observed. Squareroot, square and linear dependencies of conduction velocity on fibre diameter were used. The difference in the peak-to-peak amplitude with these relationships is small and a linear relation between amplitude and fibre diameter seems reasonable irrespective of the conduction velocity/fibre diameter relationship.
The effect of lumping the transmembrane current at the axis of the fibre is discussed. This approximation results in an underestimation of the peak-to-peak amplitude near the surface, and the error is close to 50% for very large fibres. This error is accounted for in the model.
The recording distance at which the peak-to-peak amplitude of the signal is 100 μV is found to be 400 μm in the model. This is in good agreement with values obtained from a single-fibre electrode recording. The model is computationally fast and precise. It can easily be used with few modifications to simulate single fibre action potentials recorded using different electrodes.
KeywordsAction potential Models Muscle Simulation Single fibre
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