. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. cgQ Comparative Animal Physiology In Crustacea the graded potentials of the neuromuscular junction con- tribute largely to the total action potential of the muscle. Their role in con- traction will be discussed below. In long-fibered smooth muscles, such as the anterior retractor of the byssus in Mytilns, impulses appear to be propagated at a rate of 13-20 with a simple action potential of duration 2-3 sec.^o^- when the muscle is stimulated repetitively the action potentials increase in height (sta
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. cgQ Comparative Animal Physiology In Crustacea the graded potentials of the neuromuscular junction con- tribute largely to the total action potential of the muscle. Their role in con- traction will be discussed below. In long-fibered smooth muscles, such as the anterior retractor of the byssus in Mytilns, impulses appear to be propagated at a rate of 13-20 with a simple action potential of duration 2-3 sec.^o^- when the muscle is stimulated repetitively the action potentials increase in height (staircase) and at 5-7 per second can fuse. Either there is marked fiber asynchrony or else the action potential, although conducted along the muscle, is not an all-or-none membrane depolarization but resembles more a graded end-plate potential. In the retractor of the buccal mass of Helix the action potential con- sists of two waves, fast and slow (Fig. 221 ).^'^ When stimulated through the nerve the neuromuscular junction is refractory for 10 msec, but thereafter I I M I I I I I I I I I I I I I. B Fig. 221. Action potential of fast and slow v<'aves, and mechanical record from buccal retractor of Helix. A, Response to single stimulus. B, Response to repetitive stimulation at l/sec, showing summation of contraction. Time in 1/5 second. Bolzer.*' shows supernormal excitability with maximum facilitation at 50 msec; the muscle potentials in response to stimuli at an interval of about 50 msec, summate. With repetitive stimulation at 10/sec. the muscle potential de- clines, and at 100/sec. there may be continued contraction but no demon- strable action potential.^""' The retractor muscles of Thyone also show fast and slow electrical ;" None of these long-fibered smooth muscles have been examined in regard to conduction in their single fibers. Short-fibercd and branched-fibered muscles present a difficult electrical problem. In the conduction wave of the vert
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