Active Relaxation of Unstriated Muscle


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Ramsey and Street1, working on single muscle fibres, concluded that relaxation in skeletal muscle was active. Prof. A. V. Hill2 has conclusively shown that relaxation in skeletal muscle is


passive. We stimulated the frog's rectus abdominis with potassium salts and acetylcholine and did not find any active relaxation. In unstriated muscle relaxation is active under some


conditions and passive under others3–5. In unstriated muscle there would appear to be two cycles: in one, the energy for contraction is derived from chemical stores; in the other, the energy


for contraction is derived from energy previously stored in the structure. Striated muscle appears to possess the former cycle only. This, we think, is the fundamental difference between


the two kinds of muscle.


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