Final answer:
Sympathetic preganglionic neurons are short and myelinated, whereas postganglionic sympathetic neurons are long and unmyelinated. Parasympathetic preganglionic neurons are long, and parasympathetic postganglionic neurons are short.
Step-by-step explanation:
The lengths of sympathetic neurons can be distinguished between preganglionic and postganglionic fibers. An axon from a central neuron that projects to a sympathetic ganglion is known as a preganglionic fiber, which is relatively short because the sympathetic ganglia are close to the vertebral column, and these fibers are myelinated. In contrast, postganglionic fibers—which are the axons from a ganglionic neuron projecting to the target effector—are unmyelinated and significantly longer as they must reach the distant target effectors from the ganglion.
Contrarily, in the parasympathetic system, the preganglionic fibers are quite long as they originate in the cranial region or sacral region and travel to terminal ganglia located near or even within the target organs. The postganglionic fibers in the parasympathetic system are short, projecting from the terminal ganglia a short distance to the target effector.