This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: NEET 2018, Subject name: Anaesthesia
What is mechanism of action of curonium drugs as muscle relaxant? 
Select and explain. 
A. Persistently depolarizing at neuromuscular junction, B. Act competitively on Ach receptors blocking postsynaptically, C. Repetitive stimulation of Ach receptors on muscle end plate, D. Inhibiting the calcium channels on presynaptic membrane
B: Act competitively on Ach receptors blocking postsynaptically
Answer: B: Act competitively on Ach receptors blocking postsynaptically 
Explanation: Persistently depolarizing at neuromuscular junction - propey of succinylcholine depolarising eg : succinylcholine 1. MOA - persistent / prolonged depolarising of nicotinic cholinergic receptors 2. fasiculation seen 3. post operative myalgia 4. not reversed by neostigmine 5. train of four response not seen 6. TOF ratio (B/A = 1 ) 7. neuromuscular monitoring not done 8. no post tetanic facilitation non - depolarising 1. MOA - competitive antagonist 2. fasiculation not seen 3. no post operative myalgia 4. reversed by neostigmine 5. train of four response seen 6. TOF ratio (B/A< 1 ) 7. neuromuscular monitoring done 8. post tetanic facilitation seen