Cell bodies of motorneurons are positioned between the two tracts. Most of the axons run in the right tract. The spatial relationships of axons within the bundle are highly invariant from animal to animal. These spacial relationships are highly conserved, because synaptic connections are formed 'en passant' among neuronal processes that are in immediate contact. A large number of synaptic connections is formed among the interneurons and between interneurons and motorneurons.
Arrows point from the presynaptic to the postsynaptic process.
Since synapses are formed only among processes that contact each other, the connectivity is reflected in the relative positioning of neuronal processes. It is now possible to visualize the above mentioned spatial relationship between interneuron and motorneuron axon with GFP markers. The Figure shows a short region of the ventral cord with interneuron axons labelled in green and motorneuron axons in red. Anterior is to the left, dorsal is up. There is frequent crossover between the two bundles.