What does lidocaine do?

• A. Blocks potassium channels
• B. Inhibits calcium channels
• C. Enhances sodium channel activity
• D. Blocks sodium channels to stop action potentials

Answer: (B)

Lidocaine works by blocking voltage-gated sodium channels on nerve membranes. When these channels are inhibited, the inward sodium current needed to depolarize the membrane and generate an action potential is reduced, so nerves can’t fire or transmit pain signals. This use-dependent blockade means fibers that are firing during injury are preferentially affected, giving effective local anesthesia where it's most needed. The other ideas don’t fit because blocking potassium channels would alter repolarization rather than stopping impulses, inhibiting calcium channels would mainly affect neurotransmitter release at synapses, and enhancing sodium channel activity would increase excitability rather than suppress it. So the key action is preventing action potentials by blocking sodium channels.