Acetylcholine is a chemical messenger, or neurotransmitter, that plays an important role in brain and muscle function. Imbalances in acetylcholine are linked with chronic conditions, such as Alzheimer's disease and Parkinson's disease.Acetylcholine was the first neurotransmitter discovered. Imbalances in levels of acetylcholine play a role in some neurological conditions. People who have Alzheimer's disease and