C. A. G. Wiersma

The Influence of the Frequency of Stimulation on the Slow and the Fast Contraction in Crustacean Muscle

The only exception found so far is the adductor muscle of the crayfish claw (van Harreveld and Wiersma, 1936, and Wiersma, 1937), in which a single impulse in the thick fiber elicits a strong twitch. Stimulating the thin fiber for the adductor muscle, a mechanical response can be obtained only after a number of impulses have reached the muscle. In Blepharipoda occidentalis a mechanical response was seen after stimulating the thick fiber with two induction shocks following each other with an interval of 2-10 a (Wiersma and van Harreveld, 1938). Stimulation with two shocks at longer intervals does not elicit a mechanical response, but with repetitive stimuli a contraction is still obtained with intervals up to 50 o. A single nerve impulse does elicit an action current of considerable size, however. It was found that in Blepharipoda the slow contraction was larger than the fast one up to frequencies of 50 per second. In the adductor of the walking leg of Cancer anthonyi, in which the fast mechanical contraction also needs at least two nerve impluses, the fast contraction is higher than the slow one only with frequencies above ioo per second. As these phenomena were considered of importance for the relation between the slow and the fast contraction, a number of experiments were carried out on this line to obtain further evidence.