A. Some general features of arthropod locomotion 1. Nature of appendage--usually consists of the following segments: coxa, trochanter, femur, tibia, and tarsus 2. Uses muscles that work in opposition to each other, eg., flexor-extensors, adductors-abductors, rotators, etc. 3. Muscles run across joints. Attached medially by origin and distally by insertion. 4. Power of muscle is related to cross-sectional diameter of the muscle. Because there is limited space for the larger diameter muscles, the fibers rather than running parallel to the appendage, actually run at a diagonal and insert on tendon-like structures which then pass and insert in the next segment. 5. Act as a lever, with short in and longer out. Large muscles are relegated to coxal areas and only tendons run to distal regions. This minimizes the mass of the appendage and allows for acceleration and deacceleration of the appendage. At the same time, the appendage can swing through a large arc and with great rapidity. Since velocity is related to not only the number of strides per unit of time, but also the length of the stride, animals can move rather rapidly. B. Walking or running in arthropods 1. Animal uses three appendages to form a plane, two on one side and the third on the opposite side. As the three appendages are on the substrate, other appendages can be moved forward and form a new triangle on the substrate. The previous appendages can then then be moved forward. This means that the appendages don't get tangled up with each other as they move, yet, there is always a stable platform for movement. 2. The pattern of strides is called a gait. There are different gaits associated with walking and running. 3. The pattern of limb movement is associated with the biphasic nature of locomotion in annelids, where a pair of impules pass down the length of an animal, out of phase and lateral to each other, causing progressive waves of contraction relaxation. C. Flying in arthropods 1. Nature of a foil surface--Wing acts as a foil surface, that is, it is bowed so that the air passing over dorsal surface goes at a highly velocity than the air passing over ventral surface. Thus the pressure is lower on the doral surface producing lift. Angle of attack of the wing can result in net forward motion. 2. Insect exoskeleton is quite functional with respect to flight. The exoskelton is composed of chitin, a mucopolysaccharide, that is strong, but light. For greater strength, there can be structural members, veins. 3. Important aspect of the wing surface is to facilitate lamilar movement of air over the surface and to prevent turbulent eddies from forming or if edies do form, to allow them to move off the foil surface in a fashion the minimizes drag. Drag reduces effectiveness of wing surface as foil. 4. There are two sets of muscles in the thorax, levators and depressors. The thorax also has two components, a dorsal and ventral half shells, joint laterally. Wings are at this junction. Sometimes the muscles are attached directly to the wing and move the wing up and down. Sometimes they are attached to the dorsal and ventral components of the thorax. Nerves fire a slower rate than contraction of muscles. This can happend because the exoskelton has elastic components and as the muscles contract and change the relationship of one part to the other, the exoskeleton is deformed and will return to previous shape. Thus, the nerve only needs to fire about once for each four or five muscle contractions. 5. Current thoughts are that wings developed from dorsal outgrowths in aquatic insects which were used for cooling/heating purposes. Evidence that wings function as radiators are shown by a variety of insects. Butterflies flap their wings a number of times before taking off. Bees beat their wings in a hive to heat up the hive.