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Properties of rattlesnake shaker muscle.

The goals of this study were to learn something of the physiology of the rattlesnake's rattling mechanism and the mechanical properties of tension development. Using the rattlesnakes, Crotalus atrox and Crotalus scutulatus, it was found that the rattling motion is a complex oscillation rather than the simple back and forth motion often described. Rattling is accomplished by “doublet” contractions, i.e., if the shaker muscles on one side of the tail contract, then so do the muscles on the other side. The time interval between the two members of a doublet is temperature dependent and is the ultimate determinant of maximum rattling speed. The rattling is not produced by asynchronous type muscle such as found in insects. The isometric twitch is extremely fast at 18°C, and the contraction time is on the order of 8–10 msec. The rattlesnake shaker muscle at 18°C produces 0.3 kg/cm2 tension and has a twitch-tetanus ratio of 0.19. The length-tension curve for the active muscle is typical for skeletal muscle, but there is a larger passive resistance to stretch like that found in insect fibrillar flight muscle or cardiac muscle.