<span>Norepinephrine uses the Second
Messenger System, which means, cells signal to each other what molecules have
been released that will trigger a physiological reaction. </span>
<span>
This phenomenon is activated after the ligand (ion or molecule) is bonded to its receptor
(protein molecule), creating a variation that causes a chain-reaction, that will
finally activate the Second Messenger. The latter will activate intercellular
molecules that will be able to control the cell’s activity. </span>
I think the answer here is neurons, the nerve cells
