A neurotransmitter is a chemical substance that transmits signals or impulses between neurons or from neurons to muscles. Acetylcholine is a neurotransmitter that is involved in several physiological processes, including muscle contraction, cognitive function, and memory formation. It is synthesized and released by certain neurons in the brain and peripheral nervous system and binds to specific receptors on the target cells, leading to the generation of action potentials and the subsequent transmission of signals. Other examples of neurotransmitters include dopamine, serotonin, and norepinephrine.