Clostridium botulinum is the name of the bacteria that produces botulinum toxin. Botulinum toxin is responsible for causing the fatal condition known as tetanus. However, after studying its mechanism of action several years ago, scientists began to use dilute forms of the toxin to treat some types of facial wrinkles, and it now earns billions of dollars in annual sales.
Botulinum toxin prevents the release of the stimulatory neurotransmitter acetylcholine from the axon of motor neurons, which results in the inability of muscle fibers to contract (paralysis).
Which of the following diagrams correctly depicts the action of botulinum toxin?