In clinical practice, the transmission of impulses at the NEUROMUSCULAR JUNCTION may be blocked to paralyse temporarily a patient for a surgical procedure, or to assist treatment on the intensive care unit. There are two main types of drug, both of which competitively block the ACETYLCHOLINE receptors on the motor end plates. (1) Depolarising neuromuscular blocking agents: these act by first producing stimulation at the receptor, and then by blocking it. There are characteristic muscle fasiculations (‘twitchings’) before the rapid onset of paralysis, which is of short duration (less than five minutes with the commonly used drug, suxamethonium). The drug is removed from the receptor by the enzyme, CHOLINESTERASE. (2) Non-depolarising neuromuscular blocking agents: these drugs occupy the receptor and prevent acetylcholine from becoming attached to it. However, in sufficiently high concentrations, acetylcholine will compete with the drug and dislodge it from the receptor; the effect of these drugs is reversed by giving an anticholinesterase, which allows the amount of acetylcholine at the neuromuscular junction to build up. These drugs have varying durations of action, but all are slower in onset and of longer duration than the depolarisers.