Nerve fibers of the eighth nerve and their distribution to sensory nerves of inner ear in the bullfrog

Abstract

The number of both myelinated and unmyelinated nerve fibers has been determined for the eighth nerve and each of its sensory branches in the bullfrog. No significant differences were found in the size distribution of the myelinated nerve fibers among the three ampullary nerves or between the saccular and lagenar nerves. Comparison of these two functional groups also showed no significant differences in the myelinated nerve fiber size distribution between the angular acceleration and otolithic receptors, collectively the equilibrium receptors. The wide variability, that was found not only among the animals but also between the right and left sides, most likely resulted in the absence of differences. Highly significant differences were noted when the myelinated nerve fiber diameter distributions to the acoustic organs were compared to those of the equilibrium organs. The most notable difference was the absence of any myelinated nerve fibers whose diameters were greater than 8 micrometer.