Organization of identified axons innervating the dorsal longitudinal flight muscle of Drosophila melanogaster.

Axons innervating the dorsal longitudinal flight muscle of Drosophila were investigated with physiological, light microscopic and electron microscopic techniques. Five motor axons innervate the six muscle fibres which compose a dorsal longitudinal flight muscle. All five axons, designated 1-5, are identified physiologically and morphologically. Axons 1-4 separately innervate muscle fibres 1-4, while axon 5 innervates both muscle fibres 5 and 6, making five motor units. The branching pattern of the nerve and the organization of these axons within the nerve is very consistent from fly to fly, making identification of every axon possible in both the nerve trunk and finer branches. Morphologically, axons 1-2 and 3-4 make particular pairs with long shared pathways. Furthermore, the axons are unusually closely associated with each other within the nerve.