Acetylcholine is a neurotransmitter or a chemical messenger that signals to other cells to help with several brain functions, it is the neurotransmitter that influences parasympathetic nervous system and are responsible for brain and muscle function. If that is too confusing just know that if you have too little or too much there may be neurological consequences such as Alzheimer’s or Parkinson’s Disease. It is composed of acetic acid and choline and is a part of the cholinergic system.