What are the two neurotransmitters that affect smooth muscle cells?

* Acetylcholine (ACh): ACh is a neurotransmitter that is released by parasympathetic nerves. It causes smooth muscle cells to contract.

* Norepinephrine (NE): NE is a neurotransmitter that is released by sympathetic nerves. It can cause either contraction or relaxation of smooth muscle cells, depending on the type of receptor that is activated.