Final answer:
The parasympathetic nervous system originates from the brainstem and sacral spinal cord. Epinephrine and norepinephrine are adrenal medulla hormones synthesized in response to sympathetic nervous system signals originating from the hypothalamus. The pharmacokinetics of norepinephrine depends on individual physiology but generally involves rapid action and metabolism in the liver.
Step-by-step explanation:
The parasympathetic nervous system has its preganglionic neurons originating in the brainstem and sacral segment of the spinal cord, distinct from the sympathetic nervous system which originates in the thoracic and lumbar regions. Epinephrine and norepinephrine are synthesized in the body primarily in the adrenal medulla. They are released by neural impulses from the sympathetic nervous system, and their secretion is stimulated by acetylcholine release from preganglionic sympathetic fibers innervating the adrenal medulla. In response to stress, the hypothalamus prompts the adrenal medulla to release these hormones, contributing to the fight-or-flight response. Norepinephrine pharmacokinetics involves absorption, distribution, metabolism, and excretion, with specifics depending on the route of administration and the individual's physiology. It rapidly acts and is metabolized mainly in the liver.