LOCAL ANAESTHETICS MECHANISM OF ACTION The LAs block nerve conduction by decreasing the entry of Na+ ions during upstroke of action potential (AP). As the concentration of the LA is increased, the rate of rise of AP and maximum depolarization decreases causing slowing of conduction. Finally, local depolarization fails to reach the threshold potential and conduction block ensues. The LAs interact with a receptor situated within the voltage sensitive Na+ channel and raise the threshold of channel opening: Na+ permeability fails to increase in response to an impulse or stimulus. Impulse conduction is interrupted when the Na+ channels over a critical length of the fibre (2-3 nodes of Ranvier in case of myelinated fibres) are blocked. Ref:- kd tripathi; pg num:-361