Figure 1. A schematic diagram of the motor circuit in C. elegans.

(A) Worms undulate by alternating contraction and relaxation of dorsal and ventral muscle cells lining the body. Dorsal bending is achieved when dorsal muscle cells contract (filled cells) and ventral muscle cells relax (open cells). Ventral bending is achieved when ventral muscle cells contract and dorsal muscle cells relax.

(B) General patterns of connectivity in the wiring diagram for forward movement. Arrows indicate excitatory chemical synapses from the cholinergic motor neurons (VB and DB). Blunt ended lines indicate inhibitory chemical synapses from GABAergic motor neurons (DD and VD). GABAergic neurons are dispensable for the propagation of the bending wave along the worm body during forward movement. Dashed lines indicate gap junctions between neighboring muscle cells and neighboring neurons of each cell type. Six to twelve neurons of each cell type are distributed along the worm body. The schematic diagram is based on refs. (Chen, 2007; Durbin, 1987; White et al., 1986).

(C) The morphology of DB and VB motor neurons along the circuit. All cell bodies are located in the ventral nerve cord. The axons of VB motor neurons have short anterior axons and long posterior axons. The axons of the DB motor neurons cross to the dorsal nerve cord with long posterior projections.