Answer:
I'm going off the top of my head for this one, and this is an educated guess, so check it if you would like to. When the norepinephrine binds to a protein, then the protein relays the info to the cells that are required to do the specific action. This is why we feel a sense of stress, elevated heart rates, or high alertness.
(I'm 13 so you might want to check a lot)
