How do local anesthetics decrease depolarization phase of the action potential?

How do local anesthetics decrease depolarization phase of the action potential?

• A. By blocking the sodium channel
• B. By blocking the potassium channel
• C. By opening calcium channels
• D. By increasing membrane permeability to chloride

Answer: (A)

Local anesthetics work by blocking voltage-gated sodium channels in nerve membranes, which directly dampens the depolarization phase of the action potential. During depolarization, Na+ rushes into the neuron through these channels, driving the membrane potential toward the positive. When the sodium channels are blocked, Na+ influx is reduced or prevented, so the rising phase cannot occur effectively, and the impulse cannot be initiated or propagated. Blocking potassium channels would slow or alter repolarization, not prevent the initial depolarization. Opening calcium channels would promote other processes like neurotransmitter release rather than stopping depolarization. Increasing membrane permeability to chloride would hyperpolarize the cell, making it harder to reach threshold. The net effect of sodium channel blockade is to stop the depolarization necessary for nerve impulse conduction, which is why local anesthetics produce loss of sensation.

Local anesthetics work by blocking voltage-gated sodium channels in nerve membranes, which directly dampens the depolarization phase of the action potential. During depolarization, Na+ rushes into the neuron through these channels, driving the membrane potential toward the positive. When the sodium channels are blocked, Na+ influx is reduced or prevented, so the rising phase cannot occur effectively, and the impulse cannot be initiated or propagated.

Blocking potassium channels would slow or alter repolarization, not prevent the initial depolarization. Opening calcium channels would promote other processes like neurotransmitter release rather than stopping depolarization. Increasing membrane permeability to chloride would hyperpolarize the cell, making it harder to reach threshold. The net effect of sodium channel blockade is to stop the depolarization necessary for nerve impulse conduction, which is why local anesthetics produce loss of sensation.