Once the presynaptic sympathetic fibers have arrived in the sympathetic chain they do one of three things:
- The presynaptic neuron may synapse immediately in the ganglion located at the level it entered.
- The presynaptic neuron may ascend or descend in the sympathetic trunk before synapsing in a ganglion located at a different spinal cord level.
- The presynaptic sympathetic neuron may pass through the sympathetic chain ganglia without synapsing at all, synapsing instead in a prevertebral ganglion.
In general, sympathetic innervation to structures located in the head, neck, body wall, limbs and thoracic cavity follows one of the first two courses. Sympathetic innervation to internal organs in the abdomen and pelvis follows the third course, primarily.
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