Conduction velocity of the IXth nerve fibers innervating taste organs in the rostral and caudal tongue region in bullfrog

Abstract

Sensory impulses elicited by electrical, mechanical and chemical stimulation of the fungiform papillae in the bullfrog tongue were recorded at two distant points on the glossopharyngeal nerve, and the conduction velocities of different types of sensory units in the medial branch supplying the caudal two-thirds of the tongue were compared with those in the lateral branch innervating the rostral third. (1) Rapidly-and slowly-adapting mechanosensitive units in the medial branch had the mean conduction velocity of 23 ± 0.4 (S.E.) and 14.8 ± 0.3 m/sec, respectively, the former but not the latter being significantly (P <0.001) slower than the lateral branch units of the same type by 6m/sec. (2) The velocity of gustatory unit impulses was found to range from 14 to 20 m/sec. Statistical examination revealed that the mean conduction velocities of the medial branch units can be arranged in the order of water- > sucrose- > acetic acid- = NaCl- >quinine-sensitive units. Similar order had been found in the lateral branch units, which were significantly (P <0.001) faster in the mean conduction velocity than the medial branch units of the respective type by 2 m/sec.