And it also dilates blood vessels as well as constrict other blood vessels. And the net result is more blood flows into our skeletal muscle as well as our brain, and less muscle and less blood flows into certain internal organs, such as our digestive system. Now, norepinephrine is the hormone that is used to basically constrict our blood vessels, and that means that increases the blood pressure inside our blood vessels. Now, these two molecules are also used as neurotransmitters by the nervous system. But the major difference between the neurotransmitter and a hormone is the hormone actually creates a much longer lasting effect than our neurotransmitters. So although the nervous system also uses these two molecules, it uses them as neurotransmitters.