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URA is 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.
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