Final answer:
The origin of the preganglionic fibers of the parasympathetic nervous system is the brain stem and the sacral region of the spinal cord, which forms part of the craniosacral system.
4) brain stem and the sacral region of the cord
Step-by-step explanation:
The site of origin of the preganglionic fibers of the parasympathetic nervous system is the brain stem and the sacral region of the cord. This system is also known as the craniosacral system, because the preganglionic neurons are located in nuclei of the brain stem and in the lateral horn of the sacral spinal cord. In contrast, the preganglionic fibers of the sympathetic nervous system originate from the thoracolumbar region of the spinal cord. The parasympathetic fibers are long because they extend from the brain stem and sacral region to the target organs, where they connect with terminal ganglia that are located near or within the effector organs. The postganglionic fibers, which arise from these terminal ganglia, are short in comparison because they do not have to travel a long distance to reach the target tissue within the organ.