In actual worm movement there is an alternation of dorsal and ventral contraction (worm bends up and then down) for any of the antagonistic muscle...

      In actual worm movement there is an alternation of dorsal and ventral contraction (worm bends up and then down) for any of the antagonistic muscle pairs. Synapses between interneurons exist (but are not shown in the figure), as do sensory neurons (also not shown). Suggest a mechanism that would result in the rhythmic alternation: this could involve either additional synapses or sensory neurons. Be clear, and explain your rationale.