|
The presynaptic fibers of the parasympathetic nervous system reach the locations where they synapse by one of three pathways.
1. Most commonly, presynaptic parasympathetic axons travel with their nerves of origin (or in branches that travel into the thorax) directly to ganglia.
2. In the head, some presynaptic parasympathetic axons join the course of an unrelated nerve to arrive at their postsynaptic parasympathetic neuron cell body. In this case, the parasympathetic fibers and unrelated nerve look like one structure and cannot be distinguished.
3. Finally, in the abdomen, presynaptic parasympathetic neurons pass through a sympathetic ganglion without synapsing and join a perivascular plexus to form a combined autonomic nerve plexus. They then synapse on cells within the organ wall, like good parasympathetic fibers should.
|