ANALYSIS OF MAGNETIC STIMULATION OF A CONCENTRIC AXON IN A NERVE BUNDLE

In this paper, we present an analysis of magnetic stimulation of an ax on located at the center of a nerve bundle, A three-dimensional axisym metric volume conductor model is used to determine the transmembrane p otential response along an axon due to induced electric fields produce d by a toroidal coil. We evaluate four such models of an axon located in: 1) an isotropic nerve bundle with no perineurium, 2) an anisotropi c nerve bundle without a perineurium, 3) an isotropic nerve bundle sur rounded by a perineurium, and 4) an anisotropic nerve bundle surrounde d by a perineurium, The transmembrane polarization computed along an a xon for the above four models is compared to that for an axon located in an infinite homogenous medium, These calculations indicate that a n erve bundle with no sheath has little effect on the transmembrane pote ntial. However, the presence of a perinerium around the nerve bundle a nd anisotropy in the bundle significantly affects the shape of the tra nsmembrane response, Therefore, during magnetic stimulation, nerve bun dle anisotropy and the presence of perineurium must be taken into acco unt for calculation of stimulus intensities for threshold excitation.