Acetylcholine (ACh) is a chemical messenger that acts as a neurotransmitter in the body, allowing neurons to communicate with each other and other cells. It plays a role in many functions, including: 

    Brain function: ACh is involved in brain functions like memory. 

Muscle contractions: ACh is responsible for muscle contractions that allow you to move. 
Autonomic nervous system: ACh is the primary neurotransmitter in the parasympathetic nervous system, which controls smooth muscles, blood vessels, heart rate, and bodily secretions. 

ACh is synthesized in nerve terminals from choline and acetyl coenzyme A (acetyl CoA). It's broken down by acetylcholinesterase (AChE) into acetate and choline. 
Low levels of ACh can cause muscle disorders and memory issues. Some health conditions that may be linked to ACh include: 

    Alzheimer's disease 

Myasthenia gravis, an autoimmune condition that causes muscle weakness 

Cholinesterase inhibitors are used to treat Alzheimer's disease and myasthenia gravis