The sympathetic ganglia consist of two chains of 22 seg-mentally arranged ganglia lateral to the vertebral column. The preganglionic fibers leave the spinal cord in adjacent ventral roots and enter neighboring ganglia, where they make synaptic connections with postgan-glionic neurons. Some preganglionic fibers pass through the vertebral ganglia without making synaptic connections and travel by way of splanchnic nerves to paired prevertebral ganglia in front of the vertebral column, where they make synaptic connections with postgan-glionic neurons. In addition, some sympathetic pregan-glionic fibers pass through the splanchnic nerves into the adrenal glands and make synaptic connections on the chromaffin cells of the adrenal medulla.
Because sympathetic ganglia lie close to the vertebral column, sympathetic preganglionic fibers are generally short. Postganglionic fibers are generally long, since they arise in vertebral ganglia and must travel to the innervated effector cells. There are exceptions to this generalization. A few sympathetic ganglia lie near the organs innervated (e.g., urinary bladder and rectum); thus, these preganglionic fibers are long and the postganglionic fibers are short. In contrast, the parasym-pathetic ganglia lie very close to or actually within the organs innervated by the parasympathetic postgan-glionic neurons.
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