The control of sets of motoneurones by local interneurones in the locust.

Abstract

A motoneuron innervating a muscle in a hind leg of a locust [Schistocerca americana gregaria] is controlled in a graded manner by many non-spiking, local interneurons. There is overlap and fractionation of control between these interneurons. Some interneurons depolarize the motoneuron over part of its range, others hyperpolarize it and some do both. The interneurons organize the small number of motoneurons that innervate 1 muscle into overlapping sets of various sizes. A motoneuron can be activated individually or in particular combinations with its fellow motoneurons. The motoneurons innervating 2 muscles of a joint are organized into overlapping sets by many local interneurons. This permits the motoneurons to the muscles to be activated reciprocally, together or independently. One interneuron can elicit a coordinated movement of 1, 2 or even 3 joints in a hind leg that are components of the normal behavior of the locust. A single interneuron acting alone does not usually elicit the maximum output from motoneuron, nor a complete piece of behavior. A stronger contraction of a muscle and a more complete movement results from the action of groups of interneurons. Local interneurons, exerting graded control over motoneurons may be a major element in the organization of motor patterns in the locust.