Botulinum toxin causes muscle paralysis because
a. no acetylcholine enters the synaptic cleft
b. sodium is removed from the synaptic cleft
c. the acetylcholine receptors at the motor end-plate are blocked
d. calcium is removed from the neuromuscular junction

a. no acetylcholine enters the synaptic cleft.

Explanation:

The Botulinum toxin exerts its effects by targeting nerves that release acetycholine by degrading SNARE proteins which facilitate the binding and release of acetylcholine from vesicles into the synaptic cleft.

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