THE BIOMAGNETIC SIGNATURE OF A CRUSHED AXON - A COMPARISON OF THEORY AND EXPERIMENT

The response of a crayfish medial giant axon to a nerve crush is exami ned with a biomagnetic current probe. The experimental data is interpr eted with a theoretical model that incorporates both radial and axial ionic transport and membrane kinetics similar to those in the Hodgkin/ Huxley model. Our experiments show that the effects of the crush are m anifested statically as an elevation of the resting potential and dyna mically as a reduction in the amplitude of the action current and pote ntial, and are observable up to 10 mm from the crush. In addition, the normally biphasic action current becomes monophasic near the crush. T he model reflects these observations accurately, and based on the expe rimental data, it predicts that the crush seals with a time constant o f 45 s. The injury current density entering the axon through the crush is calculated to be initially on the order of 0.1 mA/mm2 and may last until the crush seals or until the concentration gradients between th e intra- and extracellular spaces equilibrate.