Which statement best describes the mechanism of action of neostigmine in myasthenia gravis?

• A. Blocks the action of cholinesterase
• B. Stimulates the cerebral cortex
• C. Replaces deficient neurotransmitters
• D. Accelerates transmission along neural sheaths

Answer: (B)

The key idea is that neostigmine works by increasing acetylcholine at the neuromuscular junction. It inhibits acetylcholinesterase, the enzyme that breaks down acetylcholine, so more ACH remains available to bind the remaining functional nicotinic receptors. This helps improve muscle contraction in myasthenia gravis, where receptor availability is reduced.

Neostigmine does not stimulate the cerebral cortex, nor does it replace deficient neurotransmitters by supplying acetylcholine directly, nor does it speed up conduction along nerve fibers or myelin. Its therapeutic effect comes from prolonging the action of acetylcholine at the neuromuscular junction to improve transmission.