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Journal of Experimental Biology 28,22-31 (1951)
Published by Company of Biologists 1951

Giant Axons and Synergic Contractions in Branchiomma Vesiculosum

J. A. COLIN NICOL ¹

¹ Marine Biological Laboratory, Plymouth

Synergic contractions following giant axon stimulation in Branchiomma vesiculosum have been investigated by the graphic method of recording. Isotonic and isometric levers were used, and electrical stimuli from condenser discharges were applied to the surface of the animal.

Single muscle twitches occur at stimulation frequencies up to 2 per sec., above which clonus, and finally tetanus result. At high rates of stimulation fatigue rapidly sets in; this fatigue is reversible.

Data for the time course of contractions are presented. Maximal tension develops about 255 msec. after the beginning of contraction, and relaxation occupies about 1.8 sec.

Maximal tension developed isometrically under stimulation at different frequencies (12 per min. to 13 per sec.) was measured. Maximal tension is developed initially, and there is no evidence for facilitation.

Extension of the animal and of strips of the body wall under tension are described.

The results are discussed in terms of the habits of the animal, and compared with similar studies of other invertebrates.