Heat production associated with a propagated impulse in bullfrog myelinated nerve fibers.

By using heat-sensors constructed with thin film of polyvinylidene fluoride, it was found possible to detect the heat generated by myelinated fibers in the bullfrog sciatic nerve in association with a propagated impulse. The quantity of heat generated (about 0.4 microcal/g at 4.5 degrees C) is roughly two orders of magnitude smaller than that observed in nerves containing only non-myelinated nerve fibers. The smallness of the heat observed is attributed to the localization of the heat sources at the nodes of Ranvier. The major portion of the heat generated is re-absorbed by the nerve.