. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 598 Comparative Animal Physiology inhibition no contraction occurs, but facilitation may continue to be built up as shown on release from inhibition. The inhibitory fiber alone causes no observable electrical response in the muscle. When both slow excitor and inhibitor fibers are being stimulated repetitively (slow excitor as in crayfish abductor) the inhibitor fiber may cause diminution of both contraction and action potential if its impulses ar- rive less than 10 msec, (maximum 2-4 msec.) before the excitor im
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 598 Comparative Animal Physiology inhibition no contraction occurs, but facilitation may continue to be built up as shown on release from inhibition. The inhibitory fiber alone causes no observable electrical response in the muscle. When both slow excitor and inhibitor fibers are being stimulated repetitively (slow excitor as in crayfish abductor) the inhibitor fiber may cause diminution of both contraction and action potential if its impulses ar- rive less than 10 msec, (maximum 2-4 msec.) before the excitor impulses (supplemental or electrical inhibition); or the inhibitor may cause reduction of contraction only, if its impulse precedes the excitor impulses by longer times or arrives simultaneously (simple or mechanical inhibition).^^- The distinction between fast and slow responses is quantitative. The op- timum frequency in the slow fiber is lower than in the fast. At low frequen- cies (40-50/sec.) the difference in response between the two fibers is slight, but at high frequencies (over 100/sec.) the fast contraction is » The difference between the fast and slow contraction of the same muscle de- creases in the genus series: Camharus > Randallia > Blepharipoda ^Can- cer, so that in Cancer there is little difference between the two except in. A B Fig. 230. Inhibition of slow contraction (A) and of the fast contraction (B). Records from top downward are myogram, motor stimulus, timer (seconds), and inhibitor stimulus. Note greater inhibition of slow contraction, postinhibitory facilitation of fast contraction (from v. Harreveld & Wiersma^"). latency.^-''' ^^° The flexor of the carpopodite of Panulirus has five axons: four exciters and one inhibitor.^^"^ The amount of facilitation required to elicit a contraction varies with the species. The ratio of optimum inhibitory to excitatory frequencies is fairly constant for a given muscle system.^-^ For exam
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