acetylcholine (A-seh-til-KOH-leen) is a chemical made by some types of nerve cells. It is used to send messages to other cells, including other nerve cells, muscle cells, and gland cells. It is released from the nerve ending and carries signals to cells on the other side of a synapse (space between nerve cells and other cells) . Acetylcholine helps control memory and the action of certain muscles. It is a type of neurotransmitter.