Question

What are the differences between the nicotinic and muscarinic receptors?

Answer 1

Both the muscarinic and nicotinic receptors are choline receptors. The location of the muscarinic receptors include autonomic effector cells in the heart, blood vessels, eye, smooth muscles, and the glands of the gastrointestinal tract, respiratory tract and urinary tract, and also sweat glands. Nicotinic receptors are present in the neuromuscular junction, autonomic ganglia, adrenal medulla, and CNS.

Complete answer:

Muscarinic receptors	Nicotinic receptors
The Muscarinic receptors are the G protein-coupled receptors, inhibitory, and are stimulated by Muscarine and blocked by atropine.	Nicotinic receptors are ligand-gated ion channels, excitatory in nature, activated by nicotine, and blocked by tubocurarine.
The Muscarinic receptor contains $5$ subtypes of which M$1$ , M$2$ ,and M$3$ are the major subtypes.	They are a rosette-like pentameric structure that encloses the ligand-gated ion channel. There are two types of nicotinic receptors – NM and NN.
M$1$ is associated with the depolarization of autonomic ganglia, releases the histamine in which increases the acid secretion from gastric glands,	The NM receptors present in the neuromuscular junction cause contraction of the skeletal muscle.
M$2$ decreases the rate of impulse generation in the SA node, decreases the velocity of conduction in the AV node, decreases contractility of the ventricle, and decreases the release of acetylcholine from the nerve endings.	NN present in the autonomic ganglia depolarizes the NM receptors.
M$3$ enhances visceral smooth muscle contraction, constriction of the pupil, increase of exocrine secretions, the release of NO thus causing vasodilation.	enhances the release of catecholamine from the adrenal medulla, and performs site-specific excitation and inhibition in CNS.
The other two classes of Muscarinic receptors include M$4$ and M$5$ present in the nerve endings in certain brain areas that regulate the release of other neurotransmitters.	The NM receptor is antagonized by tubocurarine and NN by Hexamethonium.

Note. :
There are various agonists for the muscarinic and nicotinic receptors, that includes Oxotremorine (M$1$ ), Methacholine (M$2$ ), Bethanechol (M$3$ ), Nicotine (NM and NN). M$1$ is a Gq –protein-coupled receptor, M$2$ is Gi – protein-coupled, and M$3$ is Gq – protein-coupled receptor. DMPP (Dimethyl phenyl piperazine), PTMA( Phenyl trimethyl ammonium) are also seen to agonize the nicotinic receptors.