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Structure, function and evolution of insect flight muscle

View Article: PubMed Central - PubMed

ABSTRACT

Insects, the largest group of animals on the earth, owe their prosperity to their ability of flight and small body sizes. The ability of flight provided means for rapid translocation. The small body size allowed access to unutilized niches. By acquiring both features, however, insects faced a new problem: They were forced to beat their wings at enormous frequencies. Insects have overcome this problem by inventing asynchronous flight muscle, a highly specialized form of striated muscle capable of oscillating at >1,000 Hz. This article reviews the structure, mechanism, and molecular evolution of this unique invention of nature.

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Schematic diagram of action of flight muscles. (a), synchronous IFM; (b), asynchronous IFM. Upper trace, wing-beat; middle trace, impulses from motor nerve; bottom trace, intracellular calcium level. The broken line indicates the threshold calcium level above which contraction is initiated. Wing-beat frequencies vary greatly, depending on insect species.
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f2-7_21: Schematic diagram of action of flight muscles. (a), synchronous IFM; (b), asynchronous IFM. Upper trace, wing-beat; middle trace, impulses from motor nerve; bottom trace, intracellular calcium level. The broken line indicates the threshold calcium level above which contraction is initiated. Wing-beat frequencies vary greatly, depending on insect species.

Mentions: Like vertebrate skeletal muscle, insect flight muscle (IFM) is a cross-striated muscle, and the regulatory mechanism for its contraction and relaxation is basically identical to that of vertebrate skeletal muscle (Fig. 1): The excitation of the plasma membrane of muscle cell causes the sarcoplasmic reticulum (SR) to release calcium ions, which binds to troponin, a regulatory protein on the thin filament. This in turn causes tropomyosin (another regulatory protein) to move from its inhibitory position and initiate contraction. On the other hand, relaxation occurs as the calcium pump on the SR membrane transports the calcium ions back to the SR lumen. This transport is an energy-consuming active process done against the concentration gradient. If an IFM is to attain a high wing-beat frequency by accelerating this ordinary contraction-relaxation cycle, the volumes of both SR and mitochondria (which supply ATP as energy) must increase to keep up with an increased speed of calcium release and reuptake. This volume increase can only be done at the expense of the space for myofibrils. For this reason, an upper limit is believed to exist for the wing-beat frequencies, which is around 100Hz. The IFMs of lower insects, such as locusts (Orthoptera), operate under this limit. They contract and relax each time when an impulse arrives each time from the motor nerve. This mode of IFM operation is called “synchronous” (Fig. 2a).


Structure, function and evolution of insect flight muscle
Schematic diagram of action of flight muscles. (a), synchronous IFM; (b), asynchronous IFM. Upper trace, wing-beat; middle trace, impulses from motor nerve; bottom trace, intracellular calcium level. The broken line indicates the threshold calcium level above which contraction is initiated. Wing-beat frequencies vary greatly, depending on insect species.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC5036774&req=5

f2-7_21: Schematic diagram of action of flight muscles. (a), synchronous IFM; (b), asynchronous IFM. Upper trace, wing-beat; middle trace, impulses from motor nerve; bottom trace, intracellular calcium level. The broken line indicates the threshold calcium level above which contraction is initiated. Wing-beat frequencies vary greatly, depending on insect species.
Mentions: Like vertebrate skeletal muscle, insect flight muscle (IFM) is a cross-striated muscle, and the regulatory mechanism for its contraction and relaxation is basically identical to that of vertebrate skeletal muscle (Fig. 1): The excitation of the plasma membrane of muscle cell causes the sarcoplasmic reticulum (SR) to release calcium ions, which binds to troponin, a regulatory protein on the thin filament. This in turn causes tropomyosin (another regulatory protein) to move from its inhibitory position and initiate contraction. On the other hand, relaxation occurs as the calcium pump on the SR membrane transports the calcium ions back to the SR lumen. This transport is an energy-consuming active process done against the concentration gradient. If an IFM is to attain a high wing-beat frequency by accelerating this ordinary contraction-relaxation cycle, the volumes of both SR and mitochondria (which supply ATP as energy) must increase to keep up with an increased speed of calcium release and reuptake. This volume increase can only be done at the expense of the space for myofibrils. For this reason, an upper limit is believed to exist for the wing-beat frequencies, which is around 100Hz. The IFMs of lower insects, such as locusts (Orthoptera), operate under this limit. They contract and relax each time when an impulse arrives each time from the motor nerve. This mode of IFM operation is called “synchronous” (Fig. 2a).

View Article: PubMed Central - PubMed

ABSTRACT

Insects, the largest group of animals on the earth, owe their prosperity to their ability of flight and small body sizes. The ability of flight provided means for rapid translocation. The small body size allowed access to unutilized niches. By acquiring both features, however, insects faced a new problem: They were forced to beat their wings at enormous frequencies. Insects have overcome this problem by inventing asynchronous flight muscle, a highly specialized form of striated muscle capable of oscillating at >1,000 Hz. This article reviews the structure, mechanism, and molecular evolution of this unique invention of nature.

No MeSH data available.


Related in: MedlinePlus