MAGNETIC-FIELD RESULTING FROM ACTION CURRENTS ON CYLINDRICAL FIBERS

This paper considers the magnetic field arising from action currents associated with the propagation of an action potential along a cylindrical fiber. The equivalent current sources of the magnetic field are precisely the difference in axial current density on each side of the membrane. Fiber bundles are considered by superposition. The total magnetic field varies as 0(1/R**3) hence it is quadrupolar. The equivalent source is more strongly related to the discontinuity in conductivity between the membrane and surrounding media than directly to the ionic (primary) currents.