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Pharmacology · single question

What is the mechanism of action of botulinum toxin (Botox)?

  1. Stimulates muscle contraction by releasing acetylcholine
  2. Blocks the release of acetylcholine at the neuromuscular junction
  3. Enhances the sensitivity of muscle receptors to acetylcholine
  4. Promotes the release of acetylcholine
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Correct answer: B. Blocks the release of acetylcholine at the neuromuscular junction

  • A. No — blocking release produces paralysis, not contraction.
  • B. Correct. Botulinum toxin cleaves SNARE proteins (SNAP-25, synaptobrevin) in the presynaptic terminal, preventing acetylcholine vesicle fusion and release. The result is flaccid paralysis of the target muscle. Dental uses include masseter hypertrophy, bruxism, and gummy smile.
  • C. No — Botox acts presynaptically on the nerve terminal, not on postsynaptic receptor sensitivity.
  • D. No — this is the opposite. Botox reduces, not increases, acetylcholine availability.

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