Acetylcholine (Ach) and Norepinephrine (NE) are both chemical substances (neurotransmitters) released primarily by nerve cells and they affect different parts and systems of the body. Acetylcholine mostly targets the muscles and the brain and it is a part of the parasymphatetic nervous system whereas norepinephrine targets the whole body and has an effect that leads to the contraction of muscles and the increase of the heart rate. Norepinephrine is a part of the symphatetic nervous system.
Since the symphatetic nervous system is responsible for the crucial "fight-or-flight" response of our body, it has a more dramatic effect on the muscle contraction. Norepinephrine, being a part of the symphatetic nervous system, should result in a more drastic change in contractile force.
