Final answer:
Sympathetic preganglionic fibers are generally short and end at ganglia near the spinal column, while parasympathetic preganglionic fibers are longer and end at ganglia near or within their target organs. An exception in the sympathetic system is the fibers that end at the adrenal medulla on chromaffin cells, which directly release hormones into the bloodstream.
Step-by-step explanation:
In the autonomic nervous system, there are specific distinctions between the sympathetic and parasympathetic systems in terms of where preganglionic fibers terminate. For the most part, sympathetic preganglionic fibers are relatively short and myelinated. They tend to terminate on ganglionic neurons within the sympathetic ganglia which are located near the spinal column. From these ganglionic neurons, postganglionic fibers then extend to the target organs—that is, the organs they will influence. In comparison to the preganglionic fibers, postganglionic fibers are usually longer and unmyelinated as they cover the distance from the ganglia to the effectors.
However, there is an exception to this general pathway in the sympathetic system. Preganglionic sympathetic fibers that project to the adrenal medulla, the inner part of the adrenal gland, do not terminate in a ganglion. Instead, these preganglionic fibers end on chromaffin cells of the adrenal medulla, which serve as neurosecretory cells. These cells release signaling molecules directly into the bloodstream, functioning similarly to a postganglionic neuron even though they are part of an endocrine gland.