THE ACTION POTENTIAL WAVES TRANSMITTED BETWEEN THE SCIATIC NERVE AND ITS SPINAL ROOTS

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Abstract
Previous work has shown that the action wave in the sciatic nerve, recorded after amplification by the cathode ray oscillograph, breaks up during conduction into 4 components (alpha, beta, gamma, delta). It is now shown that the quickest component, alpha, itself is compound, consisting of the sole motor component, which passes into the ventral spinal root, and an alpha sensory component which passes into the dorsal root. The fibers contributing to these 2 waves have about the same stimulation thresholds and rates of conduction, and consequently the 2 waves are indis-tinguishably merged in the artificially stimulated sciatic nerve to form the alpha wave. It is inferred that the simple action potential wave of the phrenic nerve likewise is composed of 2 waves, the motor and the alpha sensory, indistinguishably merged, and that the alpha sensory fibers in the sciatic nerve have to do largely with muscle sense. The beta and gamma waves are entirely sensory. An indistinct delta wave also is sometimes seen in the sensory root. If the delta wave in the sensory root is made by unmyelinated fibers, this wave in the sciatic might receive contributions from both sensory and postganglionic efferent fibers. In the bullfrog the alpha sensory action wave falls behind the motor action wave 0.14 sigma (average) during its passage through the spinal ganglion. In the green frog the delay averages 0.08 sigma; in the cat it was 0.08 sigma. The delay is greater than the time an impulse would normally require to make the detour into the ganglion cell, but also insufficient to permit of the return of conductivity needed for such a detour.

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