Final answer:
A drug that blocks Na⁺ channels would inhibit neuron depolarization by preventing the influx of Na⁺ ions that is necessary for the initiation of an action potential. Potassium channel blockers would affect repolarization by slowing the exit of K⁺ ions and delaying the return of the membrane to its resting potential. so, option 4 is the correct answer.
Step-by-step explanation:
A drug that blocked Na⁺ channels would prevent neuron depolarization. This can be understood by considering how neurons generate action potentials. During the initial phase of an action potential, voltage-gated Na⁺ channels open in response to membrane depolarization, allowing Na⁺ ions to rush into the cell. This influx of Na⁺ ions results in further depolarization of the membrane. If Na⁺ channels were to be blocked, this process would be inhibited, thereby preventing depolarization and the subsequent generation of an action potential. Additionally, the repolarization phase of the action potential, which eventually leads to the restoration of the resting membrane potential, is associated with the opening of K⁺ channels, allowing K⁺ ions to leave the cell.
Potassium channel blockers like amiodarone and procainamide would specifically impact the repolarization and hyperpolarization phases of the action potential by impeding the movement of K⁺ through voltage-gated K⁺ channels. As a result, the membrane would have a prolonged depolarization phase and a delayed return to resting potential.