Inspection of the entire model shows "blue nerves" exiting the central nervous system from the brain and sacral spinal cord. These nerves run 'parallel' to those of the sympathetic division thus they were called 'para-'sympathetic. The anatomy of this division is much simpler than the sympathetic division represented by "orange nerves" in the model. Nerves of both divisions consist of paired --right and left-- two-neuron pathways. (Pairing is not illustrated in the model.)
As illistrated in the image to the right, the preganglionic cell bodies (dark blue circles) give rise to axons (solid blue lines) that extend toward their targets and end as neurosecretory terminals (blue bars) . The postganglionic cell bodies (light blue circles) lie close to, or within, the target organs. Their axons (dashed blue line) are relatively short but also end in terminals (blue bars).
Because the axons of PSNS preganglionic neurons are long, the location of ganglia are near the target organs. Accordingly, such ganglia are often described as terminal. In some cases the end of the preganglionic axon is embedded within the organ's tissues where it synapses with the postganglionic cell body (light blue circle) to form a ganglion. Ganglia of this type are often referred to as "intramural" meaning "within the wall." This is shown occurring in a gland in the small illustration.
In other cases the preganglionic axon does not enter the target organ but ends near its surface as shown by the heart in the illustration. In this case the ganglion formed at the synapse between the two neurons lies near the surface of the organ rather than within it. This type of ganglion is simply referred to as "teminal."
Last update: 9/21/2005