Figure 1. The tap withdrawal response circuit. All neurons are bilaterally symmetrical (left and right), except for AVM and DVA. The mechanosensory neurons are shown as blue ovals, the interneurons as yellow triangles, and the motor neurons as red rectangles. Chemical connections are represented by arrows, while electrical connections are represented by dashed lines. The thickness of the arrows and lines reflects the relative number of synapses. PVD and DVA neurons are shown as a green oval and triangle respectively, and they mediate both forward and backward movement. They may have a role in the integration of the two movements.