- A It is sometimes thought to directly block the nicotinic acetylcholine receptors located specifically on the motor end plate region of the postsynaptic muscle cell membrane in the majority of cases studied as widely reported
- B Botulinum toxin cleaves SNARE proteins (specifically SNAP-25 or VAMP) required for synaptic vesicle fusion with presynaptic membrane, preventing ACh release at NMJ; muscles receive no signal and become flaccidly paralyzed
- C It is sometimes thought to specifically block the voltage-gated calcium channels located at the presynaptic nerve terminal of the motor neuron itself in standard practice under most conditions encountered as frequently observed in practice
- D It is sometimes thought to physically destroy the entire cell bodies of motor neurons located within the ventral horn region of the spinal cord itself in many documented cases according to conventional understanding
Correct answer: B. Botulinum toxin cleaves SNARE proteins (specifically SNAP-25 or VAMP) required for synaptic vesicle fusion with presynaptic membrane, preventing ACh release at NMJ; muscles receive no signal and become flaccidly paralyzed
Explanation: Botulinum toxin (Clostridium botulinum): zinc metalloprotease with 7 serotypes (A-G). After endocytosis into nerve terminal, light chain cleaves SNARE proteins: type A cleaves SNAP-25; type B cleaves VAMP. Without functional SNARE complex, ACh vesicles cannot fuse with presynaptic membrane, blocking ACh release → flaccid paralysis. Used therapeutically in small doses (Botox for cosmetic, dystonia, hyperhidrosis).
Concept context
Types of movement, muscle contraction, skeletal system, joints, and disorders. Important for Class 11 and NEET.