Final answer:
The parasympathetic outflow from the nervous system comes from specific cranial nerves, particularly the vagus nerve, and sacral spinal cord roots S2-S4. It plays a vital role in controlling bodily functions related to the 'rest and digest' response, including reducing heart rate and facilitating digestion.
Step-by-step explanation:
The parasympathetic outflow from the nervous system is organized through specific cranial nerves and sacral spinal cord roots. The outflow from the cranial aspect includes the oculomotor nerve (cranial nerve III) which is associated with the Edinger-Westphal nucleus, facial and glossopharyngeal nerves related to salivatory and lacrimal gland control, and notably the vagus nerve (cranial nerve X) that innervates many thoracic and abdominal organs. Specifically, the vagus nerve carries the majority of the parasympathetic outflow to regulate essential functions of the heart, lungs, and digestive system.
Furthermore, the sacral part of the parasympathetic system exits the spinal cord at the levels S2-S4. Preganglionic neurons from the brainstem nuclei and sacral spinal cord emit axons to terminal ganglia near or within target organs, after which postganglionic neurons project to the target effectors. This system is crucial for the 'rest and digest' activities that decrease heart rate and increase digestion.