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Insect flight muscle can produce a wingbeat frequency of up to 1,000 cycles per second. Since neuronal action potentials last 1–3 milliseconds, that number of cycles per second would exceed the capacity of motor neurons, let alone the mechanism of cycling of striated muscle contraction/relaxation. The extremely fast wingbeat of a hummingbird may be only about 50 cycles per second. How do insects do it?

Vertebrate skeletal muscle and much of invertebrate skeletal muscle is called “synchronous” because the cycling of the contractile mechanism is linked to the firing of the motor neurons. Insect flight muscle does not contract in tandem with the firing of motor neurons, however, and is thus called “asynchronous” muscle. The firing of action potentials in the insect flight motor neurons is not particularly fast, but it does cause depolarization of the muscle cell membrane, the spreading of an action potential throughout the membrane, and the release of Ca²⁺ from the sarcoplasmic reticulum. However, once the asynchronous muscle fiber is stimulated, its cycle of contraction/relaxation proceeds at its own characteristic frequency as long as Ca²⁺ is available to bind to the troponin. Thus contractile cycling and the resulting wingbeat frequency are not tied to the firing rate of the flight motor neurons.