Final answer:
Norepinephrine is released at most sympathetic postganglionic nerve endings as part of the sympathetic nervous system's response.
Step-by-step explanation:
Norepinephrine is liberated at most sympathetic postganglionic nerve endings. This happens as part of the sympathetic nervous system's response, particularly during stress. All preganglionic fibers release acetylcholine (ACh), which then activates ganglionic neurons with nicotinic receptors. However, it is the postganglionic fibers of the sympathetic system that release norepinephrine onto the target organs, with the exception of those projecting to sweat glands and to blood vessels associated with skeletal muscles which release ACh. The release of norepinephrine by the sympathetic system leads to a range of physiological effects, such as increased heart rate and blood flow redirection towards essential organs.