Fibrillar type flight muscle powers the flight machinery of the more phylogenetically advanced groups of flying insects. A comparison of responses from single fibers in insects from various orders having fibrillar muscle reveals fundamental differences. In single fibers of flies and wasps the response to a single threshold stimulus is an all-or-none, uniformly rising, in most cases overshooting action potential. Beetles give variable responses, some of which appear similar to the type mentioned above, and others which summate and facilitate. Some of the latter responses vary with time in a cyclic manner, and some are altered by the intensity of the stimulus. Further differences appear when the two types of muscle are exposed to ether and carbon dioxide. In the wasp and fly ether produces a neuromuscular block, while CO2 effects a rapid depolarization of the resting fiber membrane. Both reactions are completely reversible. The electrical responses of beetle muscle are somewhat affected but only by massive doses. The implications of these data are discussed relative to the existence of fibrillar muscle "types."
展开▼
