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Both up and down insect-wing movements employ a distance-increasing lever – a lever with good speed/distance advantage [and a poor force advantage]; there.

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Presentation on theme: "Both up and down insect-wing movements employ a distance-increasing lever – a lever with good speed/distance advantage [and a poor force advantage]; there."— Presentation transcript:

1 Both up and down insect-wing movements employ a distance-increasing lever – a lever with good speed/distance advantage [and a poor force advantage]; there is a very short force arm, the moment arm of the effort is divided by the much larger moment arm of the load – the centre of gravity of the wing being much farther from the fulcrum (pleural wing process, PWP). “A muscle... is relatively good at producing force and relatively bad at getting shorter. ...any engine that gets only 20 % shorter will have to operate with a substantial distance advantage to move a long limb [wing] through an angle that may approach 180 degrees. For that good distance advantage it will necessarily suffer a poor force advantage because the product of the two must be unity...” (Vogel 2nd , p. 475)

2 Class 3 lever for both up and downstrokes of bird wings
As with the insect wing, the bird wing is a distance (speed) -increasing lever. Distance advantage will be >1, i.e., put in a small distance get out a large distance. Distance advantage: ratio of the distance moved by the load (weight of the wing) relative to that moved by the effort (contracting muscle); this is much >1. The effort arm in a flying bird is not longer than the load arm, so it is not maximizing the moment of the effort.

3 The hind (metathoracic) leg of the locust is a saltatorial adaptation
The hind (metathoracic) leg of the locust is a saltatorial adaptation. In jumping the insect moves the tibia relative to the femur using paired antagonistic muscles: the extensor of the tibia and the flexor of the tibia. The pinnately arranged fibres of these muscles, within the femur, originate on the exoskeleton’s inner surface and insert on two blade apodemes (red in diagram), one large and one small. The apodemes ‘focus’ the muscle forces to a small locus of the proximal end of the tibia. A dicondylic joint ensures that the tibial movement is in one plane. Flexion here is the same thing as depression; extension is the same as levation; so these muscles and their apodemes are also called the depressor and levator

4 Pinnate muscle via apodeme: more powerful than orthogonal (direct) fibres

5 To avoid having to draw, and only use words for organ description: see this wonderful old book of terminology for entomologists: Torre-Bueno, J.R. A Glossary of Entomology. Brooklyn Entomological Society acclivous – rising gently acetabulum – cavity into which an appendage is articulated acicular – needle-shaped (e.g. spine of Chestnut is acicular) aculeate – armed with short sharp points (e.g., burr of burrdock is not aculeate) acuminate – tapering to a long point adnate – adjoining (e.g., radius and subcosta are adnate) alate – winged etc. Takes a while to get to ‘unguis’: one of the claws at the end of the tarsus, plural ungues ETC. unguiform – shaped like a claw; unguiflexor – muscle flexing the ungues of an insect; unguifer – the median dorsal process or sclerite on the end of the tarsus to which the pretarsal claws are articulated etc. Unguiflexor lets me illustrate a rope apodeme, one specialized to convey tensile stress as well as the fact that not all antagonists are other muscles. If you really want to avoid drawing (which I don’t advise) you could concentrate on using descriptive words. See this wonderful old book which is a fine dictionary of morphological terms. For plants

6 Locust rope apodeme and unguiflexor muscles
Apodemes can also be designed for tension Locust rope apodeme and unguiflexor muscles unguiform – means claw-shaped; unguiflexor is a muscle flexing (depressing) the ungues (terminal claws) into the substratum; unguifer – the median dorsal process or sclerite on the end of the tarsus to which the pretarsal claws are articulated. Several small unguiflexor muscles (139 a,b,c) act to dig in the ungues. A locust rope apodeme is specialized to translocate tensile stress, creating effort around corners and far away at the limb tip. As in the scallop, the antagonist to muscles 139 abc i.e. the partner in the pair is NOT another muscle; it is cuticle that has become more elastic.

7 Arthropod cuticle: a hierarchical composite material Vincent J. F. V
Arthropod cuticle: a hierarchical composite material Vincent J.F.V. & Wegst U.G.K Design and mechanical properties of insect cuticle. Arthropod Structure and Development 33: Many animal materials are composites: a material made by combining two (or more?) other materials: soft composites are made of a “rubbery matrix reinforced by fibres. A “…material that is composed of two quite different materials… can have better properties than either material on its own” (Ennos 2012). My fiberglass canoe is made of a composite material, isolated glass fibres embedded in a continuous resin matrix. Cuticle, the integument of all animals in the phylum Arthropoda, functions as exoskeleton and is a composite material. Arthropod cuticle consists “…of arrangements of highly crystalline nanofibres embedded in a matrix of protein, polyphenols and water, with small amounts of lipid.” “The protein has to produce a matrix of varying mechanical properties, which will also interact with and stabilize the chitin.” It is a material, the basis of the arthropod skeleton, “praeternaturally (it means surpassing the ordinary) multifunctional” (Vincent 2004). Matrix or ‘ground substance’: a 3D-network in which fibres are embedded; a matrix of ‘mortar’ is created in a brick wall which embraces and surrounds all the bricks (cf. nachre).

8 Fig 1 from Vincent & Wegst 2004
Chitin: a “…polysaccharide akin to cellulose. The monosaccharide units link to make the molecule very straight and ribbonlike. Then nanofibres are 3 nm in diameter, 0.3 micrometeres long, in the figure they run into and out of the plane of the screen. “The fibrous composite cuticle derives its properties from its components, which can be varied in orientation... and volume fraction to produce the wide range of mechanical properties: chitin nanofibres, type of protein, water content and degree of cross-linking of the protein [sclerotization], lipid, metal ions, calcium carbonate.”

9 “Praeternaturally multifunctional” (Vincent & Wegst 2004) Cuticle/exoskeleton of animals in the phylum Arthropoda “The cuticle… not only supports the insect, it gives it its shape, means of locomotion, waterproofing and a range of localised mechanical specialisations such as high compliance, adhesion, wear resistance and diffusion control. It can also serve as a major barrier to parasitism and disease ...the insect cuticle also has to form sensors, joints, wear-resistant mandibles, devices for elastic energy storage, effective attachment systems...” (Vincent & Wegst 2004) Cuticle composition changes topographically throughout an animal’s skeleton altered to perform these various functions: it varies in strength, toughness, elasticity, dimension, shape – so it can give broad surface to muscle fibre origins (as a blade apodeme) – so it can act as a brace or strut (tentorium) - so it can translocate force around corners like a rope (unguitractor). It becomes very thin in gills so allowing the gas exchange of aquatic insects, or becomes tanned/sclerotized to resist compression and abrashion in a crushing mandible. [Sclerotization and tanning are chemical processes that toughen cuticle by creating stable cross-linkages between the nanofibres.] Adaptive form (the theme of 325) extends to the very material of the body parts: there is a hierarchially organized structure to materials – and they show adaptation throughout this hierarchy. Cuticle’s microstructure – the structure of “crystalline chitin nanofibres embedded in a matrix of protein, polyphenols and water” (Vincent & Wegt 2004) has evolved to allignments and linkages to handle force appropriately.

10 “The tensile and shear stiffnesses and strengths… are much larger when fibres are alligned parallel to the applied load.” The cuticle is secreted by a single layer of epidermal cells that covers the entire surface of the insect, extending into the tracheal system, fore- and hind gut, and part of the genital system. …It can be as thin as 1 micrometre in the hindgut and over gills [where transport matters] and as thick as 200 micrometres “(wing-covers, of large beetles) [where mechanical protection strength and toughness are needed]. The cuticle “…frequently is multilayered with a plywood-like structure “ – the grain of successive glued wood sheets is running in different directions. Wood fibres are more effective in resisting force perpendicular to the length of the fibre than along it; think of splitting a wood: hit the grain of the log on the end. Plywood analogy: “If high stiffness in more than one direction is required , as is the case in most parts of the cuticle, ‘laminating unidirectional layers in a variety of directions produces the desired properties.” Quotes from (Vincent & Wegst 2004)


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