Botulinum toxin is a neurotoxic protein produced by the bacterium Clostridium botulinum. It cleaves key proteins inside the presynaptic neurone, preventing synaptic vesicles from fusing with the presynaptic membrane.
Using your knowledge of synaptic transmission and the diagram provided, describe the normal sequence of events that occurs at a cholinergic synapse following the entry of calcium ions (Ca2+\text{Ca}^{2+}Ca2+) into the synaptic knob, and explain how botulinum toxin prevents the depolarisation of the postsynaptic membrane (sarcolemma).