The Parasympathetic Nervous System
The parasympathetic nervous system (PNS or cholinergic system):
Acetylcholine is the major transmitter of the parasympathetic nervous system, but is also the transmitter at the ganglia of both the sympathetic and sympathetic nervous systems and the somatic nervous system. Cholinergic nerves are also present within the CNS. For this reason, drugs that modulate cholinergic neurotransmission can potentially produce a range of effects. Fewer responses are achieved by using drugs which act more selectively at muscarinic or nicotinic receptors.
The steps involved in cholinergic neurotransmission are outlined below and further information is provided here.
There are two subtypes of acetylcholine receptors in the autonomic nervous system. They are outlined here. Nicotinic receptors are present at the ganglia of both the sympathetic and parasympathetic arms of the ANS as well as on the adrenal medulla. Muscarinic receptors are activated by ACh released by the postganglionic parasympathetic nerves and thus mediate the actions of the parasympathetic nervous system. In addition, muscarinic receptors mediate the actions of the sympathetic cholinergic nerves (e.g. sweating).