1. Isometric twitch and tetanic tensions were recorded from whole muscles and single motor units in isolated fourth deep lumbrical muscles from neonatal rats (most at 3-5 days old) and from older rats of various ages. 2. Whole-muscle time to peak contraction reduced from about 120 ms at birth to about 20-25 ms at 20 days and older. 3. The number of motor units in the muscle was constant with age (eleven on average) and there was no significant branching of motor axons below the common peroneal nerve branching point in the thigh. 4. In the 3-5 days age range, mean twitch:tetanus ratio for whole muscles was 0.299 and for single units was 0.177. As a consequence, mean motor unit size (as a percentage of whole-muscle tension) was greater for tetani (29.7
作者:S P, Jones;R M, Ridge
来源:The Journal of physiology 1987 年 386卷