Cholinergic receptors are part of the parasympathetic branch of the autonomic nervous system. This branch is often referred to as “Rest and Digest”, and that’s all thanks to these cholinergic receptors! They are named after their number one fan: the neurotransmitter Acetylcholine (ACh). Any drug that is a cholinergic agonist (often just called a “cholinergic”, although parasympathomimetic has a nice ring to it!) will mimic ACh, cause more ACh to be released, or prevent ACh from being cleared.
There are two main types of cholinergic receptor: Muscarinic and Nicotinic. We will get to the details of these later. You may hear drugs called “muscarinic agonists” and the like. Just know that this is referring to cholinergics of some sort.
There are a few important things to remember about cholinergic receptors:
1. When activated, they are responsible for increasing secretions (like sweat, saliva, and digestive “juices”). Think WET.
2. They work opposite, but in conjunction with,adrenergic receptors in the heart. So when they are activated, they slow the heart rate and dilate the blood vessels. To put it another way, adrenergics are the GAS, cholinergics are the BRAKES. You never have them on at the same time, but you need both of them to get places!
3. Some of them are the receptors that receive the signal for muscle contractions at the neuromuscular junctions, among many other things!