Forward or reverse movement in Caenorhabditis elegans is the result of sequential contraction of muscle
cells arranged along the body. In larvae, muscle cells are innervated by distinct classes of motorneurons. B
motorneurons regulate forward movement and A motorneurons regulate backward movement. Ablation
of the D motor neurons results in animals that are uncoordinated in either direction, which suggests that
D motorneurons regulate the interaction between the two circuits. C. elegans locomotion is dictated by
inputs from interneurons that regulate the activity of motorneurons which coordinate muscle contraction
to facilitate forward or backwards movement. As C. elegans moves through the environment, sensory
neurons interpret chemical and mechanical information which is relayed to the motor neurons that
control locomotory direction. A mechanosensory input known as light nose touch can be simulated in
the laboratory by touching the nose of the animal with a human eyebrow hair. The recoil reaction that
follows from light nose touch appears to be primarily mediated by glutamate release from the polymodal
sensory neuron ASH. Numerous glutamate receptor types are found in different neurons and interneurons
which suggest that several pathways may regulate the aversive response. Based on the phenotypes of
mutants in which neuropeptide processing is abolished, neuropeptides play a role in circuit regulation.
The light touch response is also regulated by transient receptor channel proteins and degenerin/epithelial
sodium channels which modulate the activity of sensory neurons involved in the nose touch response