7/14/2023 0 Comments Functional electrical stimulationThe internodal length is designated as l, and the ratio of internodal length to fiber diameter is assumed to be a constant (100). In this configuration (as described in Figure 21.1), the source-fiber distance is shown as h, the fiber diameter (i.e., external myelin diameter) d o, and axon diameter (internal myelin diameter) d i. In the simplest example of nerve stimulation, a point current source of strength I a is placed near a uniform myelinated fiber, and both source and nerve are considered to lie in a uniform conducting medium of unlimited extent. The results are nevertheless important as they provide a starting point toward the elucidation of more realistic models, and as some of the insights gained have wider applicability. As the reader will see, these models are fairly simple this is both an asset (in the mathematical analysis) and a limitation (since we are actually interested in more complex structures). In this and the following section, we consider the behavior of several models of nerve stimulation based on principles of electrophysiology. Consequently, several sections of this chapter are devoted to these electrode characteristics.Ģ1.2 SIMULATION OF EXCITATION OF A MYELINATED FIBER Since the flow of electricity from the electrode (where electrons carry the charges) into the tissue (where ions carry the charges) may involve an electrochemical reaction, this area must be carefully studied as well. The mechanical properties of electrodes are important particularly with respect to implants whose lifetime is measured in years. Since the electric stimulation of biological tissues requires the use of electrodes, any practical study should include consideration of electrodes and electrode-tissue interaction. These topics are discussed in the next two chapters. Another area in which electrotherapy may be applied is in the electric stimulation of cardiac tissue, including cardiac pacemakers and cardiac defibrillation. Other mechanisms that appear to be sometimes involved include thermal (heating) and neurohumoral effects.įunctional electric stimulation is a very straightforward application for the therapeutic use of electricity. In most cases, although the mechanism is not always clearly understood, it appears to arise as a consequence of the depolarization or hyperpolarization of excitable cell membranes resulting from the applied currents. There are a growing number of documented scientific therapeutic uses of electricity (Seligman, 1982).
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