VAn is a set of twelve motoneurons, distributed along the ventral cord, which innervate ventral body muscles. A typical VAn neuron (e.g. VA3 (f)) has a short, posteriorly directed process that runs in the ventral part of the process bundle. This process is always postsynaptic and receives synaptic input from AVA (*c) and AVD (*a); in addition, VA1 to VA3 receive synaptic input from AVE (*c). There are also gap junctions to AVA (b), ASn (*d) and other VAn neurons, but these may be situated on the anterior as well as the posterior processes. A long, anteriorly directed process leaves the cell body and moves to a position adjacent to the bounding basal lamina on the right-hand side of the cord, in between an adjacent ventral VBn process and a dorsal VDn process (figure 18). VAn processes have NMJs when they are in this position; the NMJs are nearly all dyadic synapses with DDn neurons as the other postsynaptic partner (a). The anterior process of a VAn eventually moves away from the NMJ region, its place being taken by the process of the adjacent anterior VAn. The anterior distal regions of the VAn processes then run for some distance in the ventral region of the cord before ending with little or no synaptic contacts with other cells. The VAn neurons at either end of the cord (i.e. VA1 and VA12) are somewhat different from the rest. VA1 (e), in common with VB1 and VD1 which are all in the region immediately posterior to the excretory duct, branches and has its NMJs arranged transversely along a confined region along the dorsal surface of the nerve cord. VA12 (g) has a similar morphology to VA2-VA11 but has some additional types of synaptic contact. It receives synaptic input from PHC, PHB, AVA and possibly VD12 and VD13. It has dyadic NMJs with VD12, VD13 and DD6 as the other postsynaptic partners. In addition VA12 also synapses onto DA8 (c), DA9 (c), DB7 (c), AS11, and PVC (d) in various combinations at multiple synapses. There are gap junctions to AVA, PHC and VB11. Magnifications: (a, c, d) x 25500, (b) x 17000.
Web adaptation, Thomas Boulin, for Wormatlas, 2001, 2002