HSN
The Mind of 
	a Worm

Members: HSNL, HSNR.

HSN is a set of two motoneurons that innervate vulval muscles in the hermaphrodite. The cell bodies of HSN are situated sub-ventrally just posterior to the vulva. A few short branches come off the processes in the vicinity of the vulva which have several synapses. The main processes enter the ventral cord and run anteriorly on either side of the ventral hypodermal ridge eventually entering the nerve ring. The processes of HSN run right round the ring near the posterior surface and end ventrally. Processes from HSN neurons were not present in the JSH animal and so, presumably, they must grow into the nerve ring sometime during or after the L4 larval stage. The main synaptic output from HSN is on the branches near the cell body. The VCn axons and the processes from HSN separate dorsally from the main body of the cord in this region (VCn-a). There are fairly large NMJs to the vm2 muscles of the vulva and synapses onto VCn (a, b). In the nerve ring the synapses tend to be rather smaller and are directed predominantly to AVF (c), BDU (d), AWB (e, f), RIF (g), AIZ (f) and AVJ. Several neurons make odd synapses onto HSN but none looks particularly significant, except perhaps BDU (*d), AVF (a) and also PLM (*g), which synapses onto HSN near its cell bodies. The processes of HSN have a gap junction between them on the dorsal mid-line (h) although they do not terminate at this point. Magnifications: (a, d, g) x 25500, (b, h) x 12750, (c, e, f) x 17000.


HSN ventral cord synapses
partners gap junctions synapses from synapses to and corecipients
VUL, NMJ - - 15
VC5 - - 5
NMJ - - 2, VC2
SABV - - 1,2 AVD
AVD - - 2 SABV, AVE
BDU - 1+2m -
AVL - 1 -
SABD - - 1
VC2 - - NMJ, Vm2
AS5 - - 1
PLM - 2 -
AVB - 1 -
AVJ - 1 -
PVQ - 1 -
PVN - 1m -
VA6 - - DA5
DA5 - - VA6
DA6 - - 1
AVG - 1m -


Web adaptation, Thomas Boulin, for Wormatlas, 2001, 2002