URAis a set of four motoneurons, which innervate muscles in the head via NMJs in the nerve ring. The cell bodies are situated anteriorly to the neuropile of the nerve ring. Anteriorly directed processes emanate from the cell bodies and run in four of the six labial process bundles. These processes do not have a ciliated ending; they peter out at about the level of the junction of the pharynx and the buccal cavity. Posteriorly directed processes from the cell bodies rejoin the process bundles and run along the outside of the ring. The bundles then turn and run anteriorly, near the inside surface of the ring, until the fibres disperse in the anterior regions of the ring. Processes from URA run along the inner surface and anterior regions of the ring neuropile and terminate laterally. URA forms distinctive NMJs in the anterior regions of the ring and, together with RIP, IL1 and RMD, makes up characteristic synaptic complexes in these regions (a, b). NMJs are nearly always adjacent to the process of an RIP cell (a, b). This represents the sole synaptic output except for a few possible synapses to RME at an NMJ region (c). The main synaptic input is from IL2 (d) and CEP. Magnifications: (a, c, d) x 25500, (b) x 12750.
Web adaptation, Thomas Boulin, for Wormatlas, 2001, 2002