What is the mechanism of action of local anesthetics?

Local anesthetics primarily function by blocking the sodium (Na+) channels that are necessary for generating and propagating action potentials in neurons. By inhibiting these channels, local anesthetics effectively prevent the depolarization of the nerve membrane, which is essential for transmitting pain signals to the central nervous system. This action results in a localized loss of sensation in the area where the anesthetic is applied.

Blocking inactivated sodium channels is particularly important because when a neuron is stimulated, sodium channels open and allow Na+ ions to flow into the cell, leading to depolarization. Local anesthetics stabilize the inactivated state of these channels, making it more difficult for them to reopen, thus interrupting the cycle of depolarization and repolarization that is necessary for the transmission of signals related to pain.

The other mechanisms listed are not the primary action of local anesthetics. They do not act by blocking potassium channels or preventing calcium entry, and they certainly do not stimulate nicotinic receptors. Instead, their effect is quite specific to the inhibition of sodium channels, making them effective for preventing nerve signal transmission, particularly for sensory and pain pathways.