DBn is a set of seven motoneurons that innervate dorsal muscles and have cell bodies in the ventral cord. A typical DBn (e.g. DB3 (e)) has an exclusively postsynaptic, posteriorly directed
process in the ventral cord that runs in the ventral regions of the cord. It receives synaptic input
from PVC (*e) and occasionally from DVA (*f). There are prominent gap junctions to AVB,
usually situated near the cell body (c). A process, which either comes directly out of the cell
body or just anteriorly to it, leaves the ventral cord and runs round to the dorsal cord as a
commissure. DB2, DB4 and DB5 run round the left-hand side of the body; the others run on
the right. The process of DBn turns and runs posteriorly on reaching the dorsal cord, with the
proximal regions of the process running adjacent to the basal lamina. There are many NMJs
in this region, most of which are dyadic, with VDn as the corecipient (a). There are also a
few dyadic synapses to DDn and VDn (b) and gap junctions to adjacent DBns (d). The distal
regions of the dorsal cord processes move away from the basal lamina and are generally devoid of any synaptic contacts.
Magnifications: (a, d) x 25500, (b, c) x 17000.
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