Propagating point-source response of active fibers

The volume conductor theory due to active nerves and muscle fibers plays an important role in understanding the potential field under normal and abnormal physiological conditions. The new concept of propagating point-source response (PPSR) separates the volume conductor filter from the active source distribution, allowing direct solutions in the time domain with greater flexibility for handling different conduction-velocity fibers and geometrically-similar limbs. Especially the tripole PPSR has good numerical properties, which are used to derive the potentials of active nerves in finite limbs. In this paper, the tripole PPSR is extended to fibers of finite lengths such as muscle fibers. Although the end effects appear for muscle fibers, no further volume conductor computations are required, and the solutions are directly obtained from the solutions for fibers of infinite lengths. The potentials at the skin surface due to a motor unit are simulated using the tripole PPSR approach