Which of the following is true of botulinum toxin?

It acts on the postsynaptic membrane of peripheral nerves to block acetylcholine receptors Botulinum toxin is the most potent bacterial toxin known. One microgram of purified toxin is able to kill 200,000 mice. The toxin is released only upon the death and autolysis of the organism, and is thus classified as an exotoxin. Its activity is limited to the peripheral nervous system, where it is internalized into the presynaptic membrane at the neuromuscular junction and blocks the release of acetylcholine. Antibiotics have no direct effect on the toxin. The currently used antitoxin is of equine origin and is usually given as polyvalent. Injection of botulinum toxin is used in medical settings to treat strabismus and blepharospasm and has gained popularity recently as a cosmetic approach to lessen wrinkles (Botox).