STUDIES ON NEUROMUSCULAR TRANSMISSION IN LIMULUS

¹ Marine Biological Laboratory, Woods Hole, Mass.

1. The electrical responses occurring in single muscle fibers of the closer muscles of the chelae of the walking legs of Limulus have been studied with the aid of intracellular electrodes and electrical stimulation of the motor axons. At the same time the total tension of the muscle was recorded at the tarsal tip.

2. The muscle is supplied by only two motor nerve fibers, one of which (the "fast" axon) evokes larger mechanical and electrical responses than does the other (the "slow" axon).

3. No inhibitory nerve fiber was found.

4. The electrical responses consist typically of junctional potentials resembling small end-plate potentials. The fast junctional potentials may give rise to small spike potentials.

5. On repetitive stimulation both axons give rise to plateaux of depolarization, from which small spikes may arise.

6. The mechanical responses consist of very small twitches to single shocks and tetani to repetitive excitation. The tetanus/twitch ratio is more than 30:1 for the fast axon, more than 100:1 for the slow axon.

7. There is post-tetanic potentiation of the twitch response of up to 5 times in the mechanical response to a single shock applied to the fast axon. This decays slowly over a period of about a minute.