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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.

No MeSH data available.


Related in: MedlinePlus

Schematic diagram showing the action on indirect flight muscle and stretch activation. Upper left, phase in which dorsoventral muscle (DVM) shortens; upper right, phase in which dorsal longitudinal muscle (DLM) shortens. Note the relation between wing position and the deformation of thoracic exoskeleton. Lower panel, relation between the forces of DLM and DVM. Stretch activation (SA) refers to the delayed rise of force after stretch. The forces of DLM and DVM are complementary to each other. The diagram shows the responses to step stretches, but in live insects, the length change is sinusoidal.
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f4-7_21: Schematic diagram showing the action on indirect flight muscle and stretch activation. Upper left, phase in which dorsoventral muscle (DVM) shortens; upper right, phase in which dorsal longitudinal muscle (DLM) shortens. Note the relation between wing position and the deformation of thoracic exoskeleton. Lower panel, relation between the forces of DLM and DVM. Stretch activation (SA) refers to the delayed rise of force after stretch. The forces of DLM and DVM are complementary to each other. The diagram shows the responses to step stretches, but in live insects, the length change is sinusoidal.

Mentions: If it is not the frequency of nerve impulses, what determines the wingbeat frequencies in these insects? In many insects, IFMs do not directly drive the wings, but do so indirectly by deforming the thoracic exoskeleton (indirect flight muscle, Fig. 4). There are two sets of major flight muscles in the thorax: the dorsal longitudinal muscle (DLM) that runs along the anterior-posterior axis and the dorsoventral muscle (DVM) that runs along the dorsal-ventral axis. These muscles work antagonistically, i.e., when one shortens, the other is stretched. Because asynchronous IFMs have the ability of stretch activation (SA), they are activated when they are stretched by the antagonistic muscle, and produce large force and stretch back the opponent. By repeating this process, insects keep beating their wings even if the calcium level does not fluctuate. Here the primary factor to determine the wing-beat frequency is the mechanical resonant frequency of the thorax and the wings. However, insects can modulate the wing-beat frequency by varying the frequency of nerve impulses, which results in a change of intracellular calcium level. In fruitfly (Drosophila), it is reported that the wing-beat frequency is increased from 185 to 195 Hz when the frequency of nerve impulses is increased from 3 to 5.5Hz7. In any event, by developing asynchronous IFM, insects have introduced a system of “distributed information processing”, which relieves the central nervous system from the burden of controlling each wing beat. This might have contributed to the realization of “microbrain” as explained earlier.


Structure, function and evolution of insect flight muscle
Schematic diagram showing the action on indirect flight muscle and stretch activation. Upper left, phase in which dorsoventral muscle (DVM) shortens; upper right, phase in which dorsal longitudinal muscle (DLM) shortens. Note the relation between wing position and the deformation of thoracic exoskeleton. Lower panel, relation between the forces of DLM and DVM. Stretch activation (SA) refers to the delayed rise of force after stretch. The forces of DLM and DVM are complementary to each other. The diagram shows the responses to step stretches, but in live insects, the length change is sinusoidal.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5036774&req=5

f4-7_21: Schematic diagram showing the action on indirect flight muscle and stretch activation. Upper left, phase in which dorsoventral muscle (DVM) shortens; upper right, phase in which dorsal longitudinal muscle (DLM) shortens. Note the relation between wing position and the deformation of thoracic exoskeleton. Lower panel, relation between the forces of DLM and DVM. Stretch activation (SA) refers to the delayed rise of force after stretch. The forces of DLM and DVM are complementary to each other. The diagram shows the responses to step stretches, but in live insects, the length change is sinusoidal.
Mentions: If it is not the frequency of nerve impulses, what determines the wingbeat frequencies in these insects? In many insects, IFMs do not directly drive the wings, but do so indirectly by deforming the thoracic exoskeleton (indirect flight muscle, Fig. 4). There are two sets of major flight muscles in the thorax: the dorsal longitudinal muscle (DLM) that runs along the anterior-posterior axis and the dorsoventral muscle (DVM) that runs along the dorsal-ventral axis. These muscles work antagonistically, i.e., when one shortens, the other is stretched. Because asynchronous IFMs have the ability of stretch activation (SA), they are activated when they are stretched by the antagonistic muscle, and produce large force and stretch back the opponent. By repeating this process, insects keep beating their wings even if the calcium level does not fluctuate. Here the primary factor to determine the wing-beat frequency is the mechanical resonant frequency of the thorax and the wings. However, insects can modulate the wing-beat frequency by varying the frequency of nerve impulses, which results in a change of intracellular calcium level. In fruitfly (Drosophila), it is reported that the wing-beat frequency is increased from 185 to 195 Hz when the frequency of nerve impulses is increased from 3 to 5.5Hz7. In any event, by developing asynchronous IFM, insects have introduced a system of “distributed information processing”, which relieves the central nervous system from the burden of controlling each wing beat. This might have contributed to the realization of “microbrain” as explained earlier.

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