Effects of Cross-union of Motor Nerves to Fast and Slow Skeletal Muscles

Abstract

THE principal difference in the dynamic properties of fast and slow skeletal muscles of the rat has been attributed to differences in their force: velocity properties¹. If this difference were maintained by specific neural influences^2,3 the primary effect of cross-union of motoneurones would be a change in the intrinsic speed of shortening of the contractile material. According to the view that the active state duration is dependent on the intrinsic speed of shortening¹, this should lead to a change in the isometric twitch contraction time which is inversely proportional to the change in speed. Furthermore, there should be no change in the twitch : tetanus ratio resulting from these changes in the force : velocity properties because the same mechanical events would take place on an altered time scale. A series of examinations is being made to test these possibilities and to determine the effects of nerve cross-union at different times after the operations. The results described below were obtained from rat extensor digitorum longus (EDL) and soleus (SOL) muscles 30–47 weeks after cross-union of their motor nerves.