Propagation of the Spike
The previous methods like the space-clamped experiments can be used to simulate the reactions of fibers with long inserted electrodes. But with those models we can also predict the voltage across the membranes of spherical cells, especially when we know the ‘injected’ stimulating current coming from the noninsulated tip of an inserted electrode. We find a different situation if we want to stimulate a nerve or muscle fiber electrically. Since the injected current leaks away on both sides of the fiber, the membrane voltage becomes a function of distance. Therefore, the situation is different from that of the space clamp, and each part of the fiber will react individually. We will overcome this difficulty by segmentation of the fiber into small cylinders with a length Δx. Within one segment the membrane behavior is similar, hence both voltage and currents may be appoximated by a mean value. Now, every segment of the fiber represents a space clamp experiment, and these can be modeled by an electric circuit, as shown in Fig. 6.1. A single segment will be simulated as a ‘local model’, e. g., with the HH equations or with any other model, as described in Chapter 5.
KeywordsIonic Current Myelinated Fiber Electrical Network Membrane Voltage Unmyelinated Axon
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