A cholinergic receptor is a certain type of cell that has a molecular structure that responds to a specific neurotransmitter called acetylcholine. These particular receptors are part of the autonomic nervous system. In addition to acetylchonline, cholinergic receptors are also sensitive to two specific types of drugs, namely nicotine and muscarine. The receptors are consequently divided into two subcategories or types, namely nicotinic receptors and muscarinic receptors, depending upon which drug affects the specific receptor.
In the human body, certain small molecules called neurotransmitters serve to transmit information from nerve endings to various cells in order to induce a specific physiological reaction. Cholinergic receptors are so named because they respond to the neurotransmitter known as acetylcholine. These particular receptors can be found in the autonomic nervous system and the brain. The autonomic nervous system, which is divided into the sympathetic system and the parasympathetic system, is part of the peripheral nervous system and triggers responses in certain internal organs and smooth muscles, including the heart. Due to their location and reaction to acetylcholine, the cholinergic receptors control certain responses that occur in the heart and other organs, including the intestine, prostate, and bladder.
Basically, acetylcholine molecules bind themselves to the receptor molecules on the cells of the receptors. An impulse of energy is generated and transmitted across a divide between the cells called a synapse or a synaptic cleft. The impulse is then carried to the affected organ or muscle, creating the desired reaction. If the impulse is carried through the sympathetic nervous system, the reaction is usually some type of stimulation, such as increased heart rate or breathing. The opposite reaction occurs if the impulse travels through the parasympathetic nervous system and will typically generate some type of relaxation response.
Aside from acetylcholine, cholinergic receptors are sensitive to certain drugs, specifically, nicotine and muscarine. Nicotine is found in tobacco and tobacco products. It can have a stimulating effect on the cholinergic receptors in the autonomic nervous system, particularly the sympathetic branch, which is the part of the autonomic system that reacts to stress factors. Similarly, muscarine, found in certain types of mushrooms, can have a stimulant effect as well, which can, among other things, affect an individual's blood flow and cause excessive sweating and unexpected bowel movements. The receptors that are affected by muscarine are not affected by nicotine and vice versa.
The process by which cholinergic receptors receive and transmit information through the autonomic nervous system is complex. While the foregoing provides a basis overview of what a cholinergic receptor is and how it functions, there are many more aspects to the process that are not covered. Research is ongoing as to the exact nature and makeup of these receptors and exactly how they respond not only to acetylcholine but to nicotine and muscarine in the human body.