On the role of the spinal afferent neuron as a generator of extracellular current.

The prediction that a system of currents flows between the dorsal column and the dorsal root due to differences in their after-potentials was found to be consistent with the experimental findings. The form, magnitude, duration, and sign of the electrotonic component DRalpha fulfill the requirements of the postulated system. A contribution of tract after-potentials to the evoked potential of intramedullary structures is indicated. It is a conclusion of this and previous studies that profound changes occur in certain membrane properties of myelinated primary afferent axons as they penetrate the central nervous system. The working concept of abrupt intraaxonal junctional regions is therefore justifiable.