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Journal of Experimental Biology 35,850-861 (1958)
Published by Company of Biologists 1958

The Electrical and Mechanical Responses of the Prothoracic Flexor Tibialis Muscle of the Stick Insect, Carausius Morosus Br

D. W. WOOD ¹

¹ Departments of Zoology, The University of Glasgow, and The Durham Colleges South Road, Durham

1. The prothoracic flexor tibialis muscle of Carausius morosus consists of two lateral rows of pinnately arranged muscle units. Motor nerve endings of the ‘Doyère-cone’ type are distributed at intervals of approximately 60 µ along each fibre. Each motor ending is probably innervated by two axons.

2. Two types of responses have been found in the muscle fibres: (i) ‘fast’ electrical responses resembling the action potential of vertebrate muscles, associated with twitch-type contractions of the fibres; (ii) ‘slow’ readily facilitating responses resembling end-plate potentials, associated with slow, smooth contractions of the muscle, and with the maintenance of tonus. There is no evidence of peripheral motor inhibition.

3. The muscle bathed in haemolymph is capable of developing a tetanus tension of 800 g./cm.² cross-sectional area of individual muscle fibres. The tetanus:twitch ratio is over 25:1.

4. Pharmacological substances which affect excitable tissues of other animals have no effect on the fast response.

5. Progressively lowered temperatures lengthen the time course and reduce the amplitude of the fast response, but an active membrane response remains at 5°C.

6. Refractoriness is evident near the peak of the fast response. The junctional potentials will summate if sufficiently close in time.

7. It is suggested that the process underlying the fast response in Carausius is similar to that in the locust and in vertebrates; but neuromuscular transmission does not appear to be cholinergic.

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