Physiological properties of the cat's first order horizontal canal neurons

Abstract

The conduction velocity and other physiological characteristics of the first order horizontal canal afferents were studied in 24 anesthetized cats. From their spontaneous firing patterns, neurons were classified into three groups : regular, intermediate and irregular. The irregular neurons tended to have a low resting rate, high sensitivity to angular acceleration, frequently exhibited adaptation during prolonged acceleration, and showed a short latency from the time of electric stimulation of the labyrinth to recording the action potential near Scarpa's ganglion. The regular units tended to have a high resting rate, low sensitivity, were mostly non-adapting, and showed a longer latency to electric stimulation. The intermediate neurons had a mixed character of regular and irregular units.
Since the latency is due predominantly to conduction in the first order axon, and since there is a direct linear relation between conduction velocity and fiber diameter in the medullated nerve fibers, it is possible to speculate that the regular cells have thin fibers which innervate the slope of the crista, the irregular neurons have thick fibers which innervate the summit of the crista, and the intermediate units have medium caliber fibers which innervate both the slope and summit of the crista ampullaris.