Some Effects of Denervation on Muscular Contraction

Abstract

The effect of denervation on contraction of the gastrocnemius of the frog was observed by recording, simultaneously, the myograms of the intact and denervated muscle. Denervation was accomplished by excising 5 to 8 mm. of sciatic nerve from one leg (7 to 21 days prior to the experiment). Thirty experiments were made on winter frogs (Rana pipiens). A gastrocnemius-sciatic preparation was made from the left (operated) and right (intact) legs. Both preparations were then mounted in such a way that the intact nerve-muscle and its writing lever were directly below the denervated muscle and in alignment with its writing lever. The muscles were stimulated by a maximal tetanus, simultaneously, through their nerves, by means of a Harvard inductorium. Stimulation was either by a switch, operated by hand or, when recurrent automatic stimulation was desired, by means of a switch placed on the kymograph and operated by its rotation. An electromagnetic signal placed in the primary circuit and arranged to write upon the drum in alignment with the two muscle levers, recorded the number and duration of the stimulations.

The myograms of denervated muscle present certain peculiar differences from those of normal muscle. The initial speed of contraction as indicated by the steepness of ascent of the lever, is greater in denervated than in intact muscle. All of the records agree in this particular. This speed factor should result in a diminished latent period for the denervated muscle. In these experiments, however, the technique was not sufficiently refined to demonstrate this difference. The relaxation phase also takes place more quickly than in the intact muscle. The difference is especially marked at the end of the relaxation phase. There appears also to be a shortening of the intermediate phase, or crest of the myogram, although this fact is less easy to demonstrate than the other two.