SAA is a set of four interneurons that send processes anteriorly up the sub-lateral cords in the head. The cell bodies of SAAD are situated in the ventral ganglion (figure 16). Those of SAAV are situated slightly dorsal of the lateral lines, closely apposed to, and posterior to, the neuropile of the nerve ring (h, i). The SAAV pair sends additional processes down the lateral lines (i). These processes run laterally alongside those of FLP for about 20 um and then end. The main processes from the cell bodies of SAAV enter the ring sub-dorsally and run round it; they then leave ventrally, on the contralateral side, and enter the ventral cord. They run posteriorly for a short distance in the cord and leave via the amphidial commissures to take up their positions along with the processes of SABV in the anterior ventral sub-lateral cords. The SAAD pair sends anteriorly directed processes into the ring, which run round it until they reach a contralateral, sub-dorsal position where they turn and run posteriorly through the ring neuropile, and then turn again to enter the dorsal sub-lateral cords along with the processes of SABD. Processes from SMBD poke into the cell bodies of SAAV, where they form chemical synapses (SMB-d). SMDcells wrap round the processes of SAA neurons ventrally (SMD-c, d). All the SAA neurons run in close association with the processes of AVA and RIM in the nerve ring; their major synaptic outputs are to these processes (a, b) and also to those of SMD. RIM synapses back onto the SAA neurons reciprocally (d). SAA has gap junctions to RMD. There are several dorsal-ventral asymmetries exhibited by these cells: PLN synapses onto SAAD (e) and ALN onto SAAV; SMBV synapses onto SAAD and makes gap junctions with SAAV, whereas SMBD synapses onto SAAV but makes a gap junction with SAAD (f). RIV (*a) synapses only onto SAAD, as does VB1, which synapses onto two posteriorly directed processes, which emanate from the cell bodies of SAAD (g); these processes end in the retro-vesicular ganglion (h) . Magnifications: (a, b) x 25500, (c) x 8500, (d-g) x 12750.
Web adaptation, Thomas Boulin, for Wormatlas, 2001, 2002