The Motor Circuit

Animal movement depends on the coordinated activities of the nervous system and the muscles it controls. Muscles that regulate locomotion and internal organ function are innervated by motor neurons residing in an axial nerve cord. Command signals enter this network from anteriorly located ganglia (e.g., brain) that extend processes into the nerve cord to synapse with local motor circuit neurons. Additional motor neurons in the "head" region may comprise a separate network for muscle functions unique to the anterior end of the animal (e.g., control of mouth parts). Although these arrays are larger and more complex in vertebrates than in non-vertebrates, this basic architecture and arrangement of motor circuit components is generally preserved in bilaterally symmetrical animals. Thus, it should be possible to exploit the simplicity and experimental manipulability of model organisms such as C. elegans to define fundamentally important features of motor circuit development and function.