Modular organization of pattern-generating circuits in a segmental motor system: The swimmerets of crayfish

Abstract

Swimmerets are paired limbs that beat rhythmically during forward swimming. Each swimmeret is innervated by a pool of about 85 motor neurons. Each pool of motor neurons is organized to produce alternating power-stroke and return-stroke activity by its own pattern-generating circuit. These circuits are anatomically separate and can function independently; each is a module of the swimmeret system. Modules in different segments do not differ in their excitability. Bilateral local interneurons and intersegmental interneurons coordinate these modules to produce the normal coordination of the system. The properties of these coordinating interneurons distinguish them from pattern-generating interneurons.