A 23 years old male presents with ingrown nail. The ingrown nail was removed after administering a ring block. The mechanism of action of the local anesthetic used is: (A) Opening of sodium channels, (B) Blockage of activated sodium channels, (C) Increased frequency of GABA activated chloride channels, (D) Increased duration of GABA activated chloride channels
Answer is B. Answer: b) Blockage of activated sodium channelsLOCAL ANESTHETICSInterfere with the excitation process in a nerve membrane in one or more of the following ways:Altering the basic resting potential of the nerve membraneAltering the threshold potential (firing level)Decreasing the rate of depolarizationProlonging the rate of repolarizationLA's are weak bases carrying a positive charge at the tertiary amine group at physiological pH.MOA: Blocks voltage gated Na+ channels from inside of cell membrane by binding to a-subunit.Nerve block produced by local anesthetics is called a nondepolarizing nerve block.LA's are weak bases; they act by penetrating the axonal membrane in the unionized form.After penetration, they get ionized and block the activated sodium channels from within, thereby preventing the propagation of action potentials.