Q. What do you mean by neurotransmitters?

- Nicotinic receptors (nicotine mimics the effects of Ach here). Found at NM-junction, ANS ganglions in general. Binding of Ach to nicotinic receptors is always excitatory (e.g. skeletal muscle contraction).

- Muscarinic receptors occur on all effector cells stimulated by the parasympathetic system. Effect of Ach on muscarinic receptors may be excitatory or inhibitory depending on target organ.

ACh -> (-) heart myocardium, however, ACh -> (+) GI tract smooth muscle

ACh is normally destroyed by ACh-ase, a degradative enzyme found on post-synaptic cells.

Nerve gas is a potent inhibitor of Ach-ase activity -> magnifies cholinergic effects, however, less potent is neostigmine (used in the treatment of myasthenia gravis).

Atropine is a reversible blocker of ACh used in cardiac rescucitation (blocks acetylcholine; so stimulates heart beat).