Electrochemistry of Insect Muscle

Abstract

Publisher Summary Insect muscles, although always striated, can be broadly classified into skeletal, cardiac and visceral muscles. The skeletal muscles originate and insert on skeletal structures (endoskeleton orexoskeleton) while the visceral muscles invest the internal organs and lack strict origins and insertions. A number of different types of insect skeletal muscle fibre have been described. These fibres differ in the number and disposition oftheir nuclei and mitochondria, in the arrangement and amount of sarcoplasmic reticulum (SR) and sarcoplasm, and in the structure of their myofibrils. Insect skeletal muscles are innervated by two main classes of motoneurone, excitatory and inhibitory. The fibres of some muscles receive endings from more than one axon—they are polyneuronally innervated. The nature of the nervous innervation is of considerable importance in terms of the electrochemistry of insect skeletal muscle fibres for it is shown that the ionic basis for electrogenesis at inhibitory synapses is strikingly different from that at excitatory synapses. Insect cardiac muscle has a micromorphology more reminiscent of insect gut muscle and muscle of the insect reproductive system than of vertebrate cardiac muscle. Information on the innervation of insect visceral and cardiac muscles and on the nervous and endocrine control of activity of these muscles is quite extensive but, as yet, rather inconclusive.