A. Acetylcholine

Acetylcholine is a quaternary ammonium compound that cannot penetrate membranes. Although it is the neurotransmitter of parasympathetic and somatic nerves as well as autonomic ganglia, it lacks therapeutic importance because of its multiplicity of actions (leading to diff use effects) and its rapid inactivation by the cholinesterases. ACh has both muscarinic and nicotinic activity.