Med J Malaya, 1960;15.


Motor nerves to voluntary muscle terminate in motor end plates applied to the muscle fibers. Between these two is a membrane with different electric potentials on each side of it. When a motor impulse arrives at the end plate, acetylcholine is released. As a result of this the electric potential difference across the membrane disappears (“depolarization”) and an electrical wave spreads from it throughout the muscle, causing it to contract. Curare blocks the action of the acetylcholine on the end plate, competing with it for a place on the end plate molecules, and so is called a “competitive blocker”. Gallamine (Flaxedil) acts in the same way. Scoline, on the other hand, causes depolarization of the end plate membrane (hence the description “depolarizing” group of relaxants) and this does not produce, as one might expect, a sustained tetanic contraction of the muscle, but renders it unexcitable so that nerve impulses produce no effect. Thus, we have our two groups of relaxants – the competitive blockers like curare, and the depolarizers like scoline (suxamethonium).