How do local anesthetics work?
The nerve fires an impulse when it becomes depolarized by a rapid influx of Na+ ions into the interior of the nerve cell. This can be described as a transient reversal of the nerve membrane to the permeability to sodium ions. The primary effect of the local anesthetic agent in producing a nerve conduction block is to decrease the permeability of the nerve membrane to (Na+) sodium ions thus preventing the influx of Na+ ions into the nerve. Therefore local anesthetics interfere with the sodium conductance and inhibit propagation of impulses along the nerve fibers, at synapses, sensory endings, and myoneural junctions. Most of the blocking action of these drugs is due to the attachment of the local anesthetic to specific binding sites inside the nerve cell. Local Anesthetics do not penetrate the myelin sheath. Small un-myelinated nerve C fibers which maintain vascular tone and transmit slow pain, and lightly myelinated nerve A-delta fibers, which transmit fast pain, are readily susceptibl
