Maximus Gage
Flight muscles are the muscles that power the wings of insects, birds, and bats. Insects have evolved unique asynchronous flight muscles to overcome the high cost of pumping Ca2+ at high frequencies. Insect flight muscles are classified functionally as direct (DFM) or indirect (IFM). Direct flight muscles are found in all insects and are used to control the wing during flight. On the other hand, indirect flight muscles involve the deformation of the thoracic exoskeleton to move the wings. Birds have two pairs of large muscles that move the wings in flight: the pectoralis and the supracoracoideus.
| Characteristics | Values |
|---|---|
| Insects' flight muscles | Direct (DFM) or indirect (IFM) |
| Primitive insects' flight muscles | Directly attached to the base of the wings |
| Insects with IFM | Diptera, Hymenoptera, and Coleoptera |
| Birds' flight muscles | Pectoralis and supracoracoideus |
| Vertebrates' flight muscles | Striated muscles |
| Insects' flight muscles | Striated muscles |
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What You'll Learn
- Insects have unique flight muscles that allow them to carry loads several times their own weight
- Insect flight muscles are classified as direct or indirect, asynchronous or synchronous, and tubular, close-packed, or fibrillar
- Direct flight muscles are used to control the wing during flight and are found in all insects
- Birds have two pairs of large muscles that move the wings in flight: the pectoralis and the supracoracoideus
- The evolution of animal flight was likely influenced by environmental factors such as high atmospheric oxygen levels and higher air density
Insects have unique flight muscles that allow them to carry loads several times their own weight
To achieve flight, insects need to beat their wings at high frequencies, and smaller insects must beat their wings at even higher frequencies due to aerodynamic reasons. For example, mosquitoes beat their wings at 500Hz, while smaller midges can beat their wings at over 1,000Hz. To overcome the challenge of powering high-frequency wingbeats, insects have evolved unique asynchronous flight muscles, a highly specialized form of striated muscle capable of oscillating at >1,000Hz.
Asynchronous flight muscles improve the efficiency of mitochondrial energy use by reducing the number of SRs and Ca2+ ion pumps required. They are activated and maintained by low-frequency neural input, and their contraction is caused by the binding of Ca2+ to TnC. Insects with asynchronous flight muscles include Diptera, Hymenoptera, and Coleoptera.
In addition to their flight muscles, insects like ants have powerful muscles relative to their body size, enabling them to carry loads several times their own weight. Ants have a greater cross-sectional area than humans, contributing to their impressive strength-to-weight ratio. Their exoskeleton also helps distribute weight across six legs, making it possible to carry large items.
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Insect flight muscles are classified as direct or indirect, asynchronous or synchronous, and tubular, close-packed, or fibrillar
Insect flight muscles are categorised in various ways, including functional classifications as direct or indirect flight muscles (DFM or IFM), physiological classifications as asynchronous or synchronous, and morphological classifications as tubular, close-packed, or fibrillar.
Direct flight muscles are found in all insects and are used to control the wings during flight. In some insects, such as dragonflies, cockroaches, and mayflies, they are also used to power flight. These muscles are attached directly to the base of the wings, and their contractions bring about the flapping of the wings.
Indirect flight muscles, on the other hand, move the wings indirectly by deforming the thoracic exoskeleton. They consist of two perpendicularly oriented, antagonistic muscles: the dorsolongitudinal muscles (DLM) and dorsoventral muscles (DVM). The DLM extends nearly parallel to the long body axis, while the DVM extends from the tergum to the sternum. This type of musculature is observed in most insects, including butterflies.
Physiologically, insect flight muscles can be asynchronous or synchronous. Asynchronous muscles are characterised by a high contraction rate, allowing insects to achieve high wing beat frequencies. They are common among small insects like flies and bees. The frequency of contraction in these muscles is independent of the frequency of activating neuronal impulses, and they are under relatively coarse control by the nervous system. Insects with asynchronous muscles have also evolved a separate neuromuscular system for fine-grained control of the wingstroke, known as "direct muscles".
Synchronous muscles, in contrast, have neural input and evoked muscle action potentials associated with each contraction. They are found in insects that beat their wings fewer than one hundred times per second, such as moths.
Morphologically, insect flight muscles can be tubular, close-packed, or fibrillar. Tubular muscles are characterised by small myofibrils evenly interspersed with mitochondria and are found in higher Orthoptera, Trichoptera, and Lepidoptera. Close-packed muscles, on the other hand, have large-diameter fibres with well-defined, large-diameter, and circular myofibrils. They are found in specific insect orders, including Coleoptera, Hymenoptera, Diptera, and Strepsiptera.
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Direct flight muscles are used to control the wing during flight and are found in all insects
Insect flight muscles are categorised as either direct (DFM) or indirect (IFM). Direct flight muscles are used to control the wing during flight and are found in all insects. They are attached directly to the sclerites that make up the wing hinge and are contracted with 1:1 impulses from motor neurons.
The wings pivot up and down around a single pivot point. The wings are raised by a contraction of muscles attached to the base of the wing inside (toward the middle of the insect) the pivot point. The wings are then lowered by a contraction of muscles that attach to the wing outside of the pivot point. In some insects, such as dragonflies, cockroaches, and mayflies, direct flight muscles are also used to power flight.
In insects with indirect flight muscles, the power-producing muscles move the wings indirectly by deformation of the thoracic exoskeleton. The IFM consists of two perpendicularly oriented, antagonistic muscles: the dorsolongitudinal muscles (DLM) and dorsoventral muscles (DVM). The DLM extend nearly parallel to the long body axis while the DVM extend from the tergum to the sternum.
The majority of insects use IFM distortion of their thorax structure to produce wing flapping. The muscles in the thorax attach to the thorax and deform it; since the wings are extensions of the thoracic exoskeleton, the deformations of the thorax cause the wings to move as well. This indirect actuation of the wings through deformation of the thorax is a unique flight mechanism that is widely observed in most insects.
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Birds have two pairs of large muscles that move the wings in flight: the pectoralis and the supracoracoideus
Flight is an energetically demanding activity for animals. Muscle-powered flight has evolved in insects, birds, and bats. The evolution of flight muscles in these species has been influenced by the requirement for highly efficient and sustainable contractions to power their wings during flight.
The supracoracoideus muscle is the primary wing elevator, responsible for raising the wings during the upstroke. It lies in the angle between the keel and the plate of the sternum and along the coracoid, achieving a pulley-like action through a tendon that passes through the canal at the junction of the coracoid, furcula, and scapula. The supracoracoideus muscle is relatively smaller than the pectoralis, but its size varies between bird species and increases with body size. For example, in pigeons, the supracoracoideus is only one-fifth the size of the pectoralis, while in penguins, auks, swifts, and hummingbirds, it is relatively larger.
Both the pectoralis and supracoracoideus muscles shorten over a large fraction of their resting fibre length (33-42%) during each wing stroke, enhancing the work they perform during subsequent shortening. This allows them to produce the considerable power needed to support the bird's weight in the air and overcome drag.
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The evolution of animal flight was likely influenced by environmental factors such as high atmospheric oxygen levels and higher air density
Flight muscles are the key organ system that enables insects to fly. They can produce the highest known metabolic power input and mechanical power output of any organism, allowing them to carry loads several times their own weight. Insect flight muscles are classified as either direct (DFM) or indirect (IFM). Direct flight muscles are used by all insects to control their wings during flight, and by some insects, such as dragonflies and cockroaches, to power their flight. The wings are raised and lowered by the contraction of muscles attached to the base of the wing inside and outside of a single pivot point.
The evolution of animal flight has occurred separately at least four times: in birds, bats, insects, and pterosaurs. Insects evolved flight much earlier than birds or bats and did so with much smaller body sizes. The evolution of flight in both vertebrates and invertebrates has led to a wide range of adaptations to exploit unique physiological advantages and overcome deficiencies.
In addition to oxygen levels, air density is also a critical factor in animal flight. Studies on the common fruit fly, Drosophila melanogaster, have shown that atmospheric density directly impacts the ability of flies to fly. These studies suggest that there may be a critical atmospheric density threshold below which active flight is unfeasible, which could significantly impact biosphere development. Therefore, higher air density in the past may have facilitated the evolution of animal flight.
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Frequently asked questions
Flight muscles are muscles that power the flight of insects, birds, and bats.
Insect flight muscles are classified as direct (DFM) or indirect (IFM). Direct flight muscles are found in all insects and are used to control the wing during flight. In insects such as dragonflies, cockroaches, and mayflies, direct flight muscles are also used to power flight. Indirect flight muscles move the wings by deforming the thoracic exoskeleton.
The wings of birds are moved by two pairs of large muscles: the pectoralis, which lowers the wing, and the supracoracoideus, which raises it.
The evolution of flight muscles in insects, birds, and bats is an example of convergent evolution. The high atmospheric PO2 (partial pressure of oxygen) during the emergence of animal flight may have increased the systemic metabolic potential and physical activities of animals, allowing them to reach the requirement of flight.
