Innervation of Coxal Depressor Muscles in the Cockroach, Periplaneta Americana

Abstract

The innervation of the mesothoracic and metathoracic coxal depressor muscles has been investigated using intracellular microelectrodes. Five motor axons have been found to innervate the coxal depressor muscles; the largest is a fast axon, the second largest a slow axon and the three smallest are all inhibitory axons. The fast axon innervates the anterior and posterior coxal depressor muscles as well as parts of the coxal branches of the main leg depressor muscle. The slow innervates all fibres in the coxal branches of the main leg depressor muscle. The three inhibitory axons innervate only those parts of the coxal branches of the main leg depressor muscle which are not innervated by the fast axon. The three inhibitory axons were found to be branches of three different common inhibitory motoneurones.