... peripheral nervous system (PNS). It also acts on nicotinic receptors but they will not be considered in this experiment. There are 5 types of Muscarinic receptors. M1, M2, and M3 are well characterised. M4 and M5 are of doubtful physiological significance and will not be considered3. M1 receptors are mainly found on CNS, peripheral neurones and gastric parietal cells 3.They are selectively blocked by Pirenzepine. M2 receptors are found in the heart and in the presynaptic terminals of peripheral and central neurones. They exert inhibitory effects. Methoctramine is a M2 selective antagonist 3,4. M3 receptors are found on glandular tissue and on smooth muscle. 4-DAMP is a selective antagonist for this receptor. They are all activated by acetylcholine and blocked by atropine 3,4. Differing subtypes can be distinguished through their selective antagonists and agonists. Atropine, 4-DAMP, Methoctramine and Pirenzepine and Oxybutynin are antagonists. Carbachol is an agonist, it is similar in structure ...

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