Motor Units of the First Superficial Lumbrical Muscle of the Cat

Abstract

Forty-three motor nerve fibers supplying single motor unit in the first superficial lumbrical muscle of the cat were isolated in the 1st and 2nd sacral ventral roots. The conduction velocities of these nerve fibers ranged between 90 and 43 m/sec. The twitch contraction times of lumbrical motor units were evenly distributed within the range of 15 to 45 msec. The 2 parameters, conduction velocity and contraction time, were found to be linearly related. High conduction velocity corresponded to short contraction time and vice versa. The maximal tetanic tension developed by a slow motor unit was smaller than the tension developed by a fast unit. The tetanus/twitch tension ratios for different motor units differed considerably indicating the twitch tension values to be influenced by series elastic components. No relation could, however, be found between these ratios and the contraction times of the units. Differences in contraction times are due to time differences in motor unit characteristics.