The central nervous organization underlying control of antagonistic muscles in the crayfish. I. types of command fibers

Abstract

Abstract 1. A limited number of “command” interneurons mediate the release of coordinated ganglionic output to antagonistic postural muscles in the crayfish abdomen. Graded contractions of these muscles are regulated by the frequency of discharge in several motoneurons, whose own discharge is in turn controlled by the level of activity in command fibers. 2. Different command fibers having a similar effect (i.e., flexion or extension) vary in the relative effectiveness with which they excite specific motoneurons. This selectivity is responsible for different rates of tension development. 3. Command fibers connect with the postural motor system in each segment in a bilaterally symmetrical fashion. Many of the same command elements also have unilateral or reciprocal effects on other motor systems, especially on those which control the swimmerets and uropods. 4. The reciprocity between flexors and extensors is inherent in the ganglionic organization. Activation or modulation of this ganglionic center is accomplished by the command interneurons, which in turn are activated by appropriate combinations of sensory inputs. A wide variety of postural adjustments may thus be controlled by a limited number of central neurons that make complex but specific output connections.