Lecture 19 - Paper 2: Introduction to Insect Flight Muscles - Asynchronous Muscle The insect body is organized into the head, thorax, and abdomen. The wings and legs are located on the thorax. Insects have an exoskeleton composed of stiffened plates of chitin connected by flexible joints. Introduction to Insect Flight Muscles - The major muscles that are flapping the wings up and down are not pulling on the wings themselves and they move the wings up and down by changing the shape of whole exoskeleton/thorax region 2 major muscles: - The dorsoventral muscles contract, depressing the tergite (notum), which raises the wings and stretches the dorsal longitudinal muscles. - The dorsal longitudinal muscles contract, bending the tergite into an arch, which lowers the wings and stretches the dorsoventral muscles. - Other muscles adjust the angle of the wings to control direction during flight. - When the dorsoventral muscles contract, this pulls on the dorsal and ventral side pulling them closer together compressing the thorax which depresses the tergite causes the wings to rise - When dorsal longitudinal muscles contract, bends the tergite makes it into an arch which is much higher and a series of joints in the exoskeleton and thru these series of joints the change of shape of the tergite translates to lowering the wings - Alternating between the contraction of dorsoventral muscles and the dorsal longitudinal muscles is what's flapping the wings up and down and every time the wings are going down generates the lift required for flight so it's pushing against the air raising the insect's body upwards - When the dorsoventral muscles contract, this stretches the longitudinal muscles and when the dorsal longitudinal muscles contract, since it raises up the tergite it stretches the dorsoventral muscles so these muscles are alternating between contracting and being stretched
Site of cross-section Edward Snelling (A) Tergite: depressed Dorsal longitudinal muscles: relaxed Wing Digestive tract 00 Dorsoventral muscles: contracted Pivot (fulcrum) Tergite: arched Dorsal longitudinal muscles: contracted Invertebrates, Second Edition. Figure 17.16. C 2003 Sinauer Associates, Inc. Dorsoventral muscles: relaxed Clicker: So far this term, we have studied synchronous muscle. What is a major difference between synchronous muscle and asynchronous muscle? Answer: In synchronous muscles, each action potential stimulates a single contraction (or contributes to maintaining tetanus), while in asynchronous muscles, a single action potential can stimulate a series of contraction and relaxation cycles. - . Most synchronous muscles are capable of contracting at higher frequencies than asynchronous muscles. - Not true as some skeletal muscles (sonic muscles) can contract quite quickly but these asynchronous muscles can contract even faster than most sonic muscles. · Only vertebrates have synchronous muscles, while most other animals have asynchronous muscles. - Many insects have asynchronous muscles and some vertebrate muscles/cardiac muscle can contract in an asynchronous way . In synchronous muscles, an action potential results in the release of Ca2+ from the sarcoplasmic reticulum - this increase in cytoplasmic [Ca2+] allows contraction. In asynchronous muscles, an action potential results in