All of the previous neurophysiological studies on DC potentials had been made on the brain.
The existence of similar electrical phenomena in the peripheral nerves could only be conjectured, but it
was a necessity to relate the measured surface potentials to the total CNS. To investigate this further we
measured the DC potentials along 1 cm segments of various peripheral nerves (18). Again,
reproducible DC voltages were found; however, their polarity appeared to be dependent upon the
direction of the normal nerve impulse travel. Sensory nerves were polarized distally positive, while
motor nerves were polarized distally negative. Combined nerve trunks, with both sensory and motor
components, demonstrated polarities and magnitudes of potentials that were related to the arithmetic
addition of the potentials associated with each component. (It should be remembered that while all
peripheral nerves are called axons, only those that are motor are truly so; the sensory fibers are in
reality dendrites carrying information centrally.) These measured polarities seemed to indicate that
each complete neurone was polarized in the same direction along its axono-dendritic axis. These
observations almost exactly paralleled those made by Libet and Gerard on the cerebral neurones 30
years before. Thus the body surface fields measured by Burr and Lund, rather than being the result of
the electrical activity of all the cells, appeared to be associated with some DC activity of the entire
nervous system. The electrical potentials measured longitudinally along the peripheral nerves paralleled
in magnitude the general state of the CNS "in toto," (i.e., they diminished with anesthesia and with
section of the spinal cord). Since they could be measured constantly during periods of relatively normal
CNS state, it was postulated that they had to be generated by a constant current flow.
Fig. 2.2. Plots of the surface DC electrical potential on the surface of the salamander as reported by
Burr (left) and found by us (right). The central nervous system is diagrammed in the center. The
relationship between the complex field and the nervous system is evident.
Fig. 2.3. Measured DC electrical potentials along segments of peripheral nerves of the frog. The
sensory nerves were found to be distally positive while motor nerves were distally negative. The
arrangement of motor and sensory nerves in the typical reflex arc is shown in the center diagram. The
conclusion reached is that neurones have an overall longitudinal electrical polarization as shown on
the left.
As a means of further substantiating this idea and possibly determining the type of charge
ELECTROMAGNETISM & LIFE - 27