Final answer:
Parasympathetic fibers originate within the (Option b) brainstem and sacral spinal cord. This system is known for regulating the 'rest-and-digest' responses by releasing acetylcholine on target tissues through the parasympathetic nervous system.
Step-by-step explanation:
The parasympathetic fibers originate within the brainstem and the sacral spinal cord. These preganglionic fibers of the parasympathetic nervous system travel in cranial nerves and spinal nerves, projecting to terminal ganglia located near or within the target effector organs. The preganglionic fibers release acetylcholine (ACh) onto nicotinic receptors to excite the ganglionic neurons, and the postganglionic fibers then contact the target tissues to release ACh, which binds to muscarinic receptors to induce 'rest-and-digest' responses.
Therefore, the correct answer to the student's question is B) brainstem, sacral spinal cord.