Acetylcholine (often abbreviated ACh) is a neurotransmitter found within the central nervous system and peripheral nervous systems (which is comprised of the autonomic nervous system and somatic nervous system). It is one of the neurotransmitters responsible for excitatory neuronal transmission in the CNS, as well as excitatory stimulation of skeletal muscle action potentials that produce contraction. In the autonomic nervous system, it is released from all pre-ganglionic neurons, as well as post-ganglionic neurons of the parasympathetic system, including the Vagus nerve that innervates the gastrointestinal tract and heart. Additionally, acetycholine is used to stimulate the modified sympathetic ganglion that is the adrenal medulla, as well as stimulation of sweat glands.
Neurons that secrete acetylcholine are called "cholinergic". There are two distinct types of receptors for the neurotransmitter, named after the agonists used in their discovery, Nicotinic and Muscarinic. The former is an ionotropic receptor (ion channel) and is the principle receptor located at the neuromuscular junction, while the latter is coupled to G proteins to mediate ion conductance.