Question

Lidocaine is a topical anesthetic used to treat minor muscular pain and skin irritation. As shown in the diagram below, lidocaine can exist in an ionized state and an nonionized state. According to this diagram, which of the following statements best explains how lidocaine directly exerts its anesthetic effects?

A. lidocaine blocks a neural cell membrane from depolarizing, causing the neuron to be unable to transmit an action potential.
B. lidocaine prevents the release of neurotransmitters from the axon of the transmittinf neuron.
C. lidocaine binds to external surfaces of channel proteins embedded in the neural membrane, which blocks movement of ions into the cell.
D. lidocaine activates sodium channels to open, causinf rapid depolarization of the neuronal membrane.​

Answer 1

A. Lidocaine blocks a neural cell membrane from depolarizing, causing the neuron to be unable to transmit an action potential.

Step-by-step explanation:

Lidocaine works by blocking the voltage-gated sodium channels in the neuronal membrane, which prevents the depolarization required for the neuron to transmit an action potential. This blockage occurs preferentially in the ionized form of lidocaine, which can bind to the inside of the sodium channels. The nonionized form of lidocaine can more easily penetrate the lipid membrane of the neuron and reach the sodium channels from inside the membrane, where it can then become ionized and block the channels. This results in a local anesthetic effect, as the neuron is unable to transmit signals of pain or discomfort.