<prompt> Botulinum toxin blocks neuromuscular transmission by the following mechanism:Closure of Ca channels at presynaptic membraneClosure of Na channels at the postsynaptic membraneOpening of K channels at the presynaptic membraneOpening of Cl- channels at the postsynaptic membrane  <response>: Ref:KD Tripathi pharmacology 7th edition page.no: 99 Botulinum toxins A and B are highly potent exotoxins produced by Clostridium botulinum that is responsible for Botulism. These neurotoxic proteins cause long-lasting loss of cholinergic transmission by interacting with axonal protein involved in exocytic release of Ach and thereby closing the calcium channel in the pre synaptic membrane 