Final answer:
Norepinephrine is used as a neurotransmitter by the sympathetic nervous system in the fight or flight response. It is released by postganglionic sympathetic fibers and acts as a hormone in the bloodstream from the adrenal medulla.
Step-by-step explanation:
Norepinephrine is also used as a neurotransmitter by the sympathetic nervous system in the fight or flight response. Norepinephrine is released by most postganglionic sympathetic fibers and also as a hormone into the bloodstream from the adrenal medulla. At high levels, it binds to specialized alpha (a) receptors.
Learn more about Norepinephrine as a neurotransmitter in the sympathetic nervous system