URB is a set of two interneurons with cell bodies situated laterally, anteriorly to the nerve ring. Processes directed anteriorly from the cell bodies run up in the lateral process bundles. These processes peter out, with no terminal specializations, at about the level of the junction of the buccal cavity and the pharynx. The posterior branches from the cell bodies run along the outside of the nerve ring and then turn and run anteriorly and ventrally, near the inner surface of the nerve ring, eventually ending sub-ventrally. URB processes partly wrap round those of SMB (c) sub-dorsally in a characteristic manner. The main synaptic output is to URX (a), CEP (b), RIC (d) and IL1; there is some reciprocal synaptic input from CEP. There are gap junctions to OLQ (*e) at the distal ends of the processes in the ring. Magnifications: (a, d) x 25500, (b, c) x 12750.
Web adaptation, Thomas Boulin, for Wormatlas, 2001, 2002