Abstract
The cholinergic receptors are the site of action of acetylcholine (Ach) and acetylcholine like substance and anti-cholinergic agents, these receptors either muscarinic receptors or nicotinic receptors the exactly difference between them the area of receptor, where the muscarinic receptor is short than nicotinic receptor (nearly 4.5 and 6 Angstrom, respectively) and the muscarine act on muscarinic receptors and nicotine act on nicotinic receptors. The direct cholinomimetics and cholinergic blocking agents are characterized by chemical features adjustment with these receptors. This can be explained by the structure activity relationship (SAR) of direct cholinomimetic and cholinergic blocking agent drugs. The important examples of stereo specificity of receptors are hexamethonium and decamethonium, which is binding with the nicotinic receptor by specific mechanism (via width and length respectively of the receptor).