Acetylcholine receptor

Acetylcholine receptors function throughout the nervous system including the parasympathetic nervous system and are "cell surface proteins that bind acetylcholine with high affinity and trigger intracellular changes influencing the behavior of cells. Cholinergic receptors are divided into two major classes, muscarinic and nicotinic, based originally on their affinity for nicotine and muscarine. Each group is further subdivided based on pharmacology, location, mode of action, and/or molecular biology."

Classification
Acetylcholine receptors are divided into muscarinic and nicotinic receptors.

Muscarinic receptors
There are five types of muscarinic receptors.

M1 receptor
The M1 receptor is in the peripheral ganglia.

M2 receptor
The M2 receptor is a "specific subtype of muscarinic receptor found in the lower brain, the heart and in smooth muscle-containing organs. although present in smooth muscle the m2 muscarinic receptor appears not to be involved in contractile responses."

M3 receptor
The M3 receptor is found in smooth muscle-containing organs.

M4 receptor
The M4 receptor is a "specific subtype of muscarinic receptor found in the corpus striatum and the lung. it has similar receptor binding specificities to muscarinic receptor m1 and muscarinic receptor m2."

M5 receptor
The M5 receptor is a "specific subtype of muscarinic receptor found in a variety of locations including the salivary glands and the substantia nigra and ventral tegmental area of the brain."

Nicotinic receptors
Some authors subdivide nicotinic receptors into N1 and N2 receptors.

N1 receptor
N1 receptors are in the neuromuscular junction. These are susceptible to snake α-toxins.

Antibodies to the N1 receptor is the most common cause of myasthemia gravis.

N2 receptor
N2 receptors in ganglia. These are resistant to snake α-toxins.