THE FUNCTION OF DIPTERAN FLIGHT-MUSCLE

The flight muscles of flies are separated into two physiologically, an atomically, and functionally distinct classes: power muscles and contr ol muscles. The large indirect power muscles sustain the high level of mechanical energy required to flap the wings up and down during fligh t. The contractions in the asynchronous power muscles are initiated by stretch, and their slow presynaptic motor drive serves only to mainta in a tonic level of cytosolic calcium. Although providing the mechanic al energy for flight, the power muscles are not directly attached to t he wings. Instead, their mechanical energy is transmitted to the base of the wings through the complex linkage system of the wing hinge. In contrast, the small control muscles insert directly onto the skeletal elements at the base of the wing. Through their mechanical effects on the hinge, the control muscles act collectively as a transmission syst em that determines how the mechanical energy produced by the power mus cles is transformed into wing motion. The control muscles are activate d by motor spikes in the conventional one-for-one fashion. Thus, altho ugh the control muscles can generate little mechanical power, they pro vide the means by which the nervous system can rapidly alter wing kine matics during sophisticated aerial maneuvers. Copyright (C) 1997 Elsev ier Science Inc.