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The effect of denervation on the contractile properties of skeletal muscle Webster, Deirdre M. S.


The literature has provided ample evidence that neural influence is responsible for the regulation and maintenance of muscle properties. This study, conducted on approximately 100 mice of the C57 BL/6J+/+ species investigated the differential effects of denervation on the isometric contractile properties of a fast-twitch (extensor digitorum longus) and a slow-twitoh (soleus) muscle. Adult male animals were studied at 1, 28, 84 and 210 days following unilateral section of the sciatic nerve. The muscles were stimulated in vitro at 37°C at optimal length by supramaximal square pulses. The data for all muscles in each experimental group were pooled and compared to age-matched controls. In both the denervated soleus (SOL) and extensor digitorum longus (EDL) the time-to-peak twitch tension and the half relaxation were prolonged by 28 days post-denervation and this trend continued to the oldest age groups studied. The weight of the denervated muscles was less than that of the controls. Consequently, although the force that could be generated per unit mass by the EDL was initially well maintained, all muscles showed reduced peak tetanic tension in the long term, following denervation. Even when developed tension was expressed on a per wet weight basis, soleus became weaker with increased time post-denervation. A surprising and unexpected-result was the finding that 28 days after denervation both the fast and slow-twitch muscles developed increased tension. The denervated SOL showed a marked decrease in resistance to fatigue at 1 and 28 days, whereas the EDL showed an increase in resistance to fatigue at 28 days and beyond. It was concluded that denervation affected the tension generating ability and the contraction time of the SOL more than the EDL. The fatigue response indicated that conversion of fibre types may have occurred in the EDL and to a lesser extent in the SOL. The results support the hypothesis that slow muscle may be more dependant upon neural influence than fast muscle for the maintenance of its contractile properties. Further experiments to test this hypothesis are outlined.

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