What causes local anesthesia to work?

What causes local anesthesia to work?

• A. Decreases the rate of depolarization
• B. Increases the rate of depolarization
• C. Increases threshold potential
• D. Decreases membrane permeability to potassium

Answer: (A)

Local anesthesia works by blocking voltage-gated sodium channels in nerve membranes. This prevents sodium from entering the neuron during the upstroke of the action potential, so the rapid depolarization that normally propagates along the nerve is slowed. With a slower rate of depolarization, the nerve fiber cannot reach the threshold quickly enough, and the action potential fails to propagate beyond the blocked site, blocking signal transmission and producing anesthesia. This effect is not about changing potassium permeability or increasing depolarization rate; the key action is the reduced rate of depolarization due to sodium channel blockade.

Local anesthesia works by blocking voltage-gated sodium channels in nerve membranes. This prevents sodium from entering the neuron during the upstroke of the action potential, so the rapid depolarization that normally propagates along the nerve is slowed. With a slower rate of depolarization, the nerve fiber cannot reach the threshold quickly enough, and the action potential fails to propagate beyond the blocked site, blocking signal transmission and producing anesthesia. This effect is not about changing potassium permeability or increasing depolarization rate; the key action is the reduced rate of depolarization due to sodium channel blockade.