text: There are several theories put forward by which a local anesthetic  agent works. The commonly accepted theory is the "Specific Receptor Theory".. The local anesthetic agent binds to certain receptors on the cell membrane and exert their action.The sequence of action are as follows:\n * Displacement of calcium ions from nerve receptor site..\n * Binding of local anesthetic molecule to this receptor site..\n * Blockade of sodium channel.\n * Decrease in sodium conduction.\n * Depression of rate of electrical depolarization.\n * Failure to achieve threshold potential level.\n * Lack of development of propagated action potential.\n * Conduction blockade.\n  \n   As for as the routes are concerned, LA can be given as:\n * topical application.\n * infiltration under the skin or mucous membrane to block peripheral nerves.\n * intramuscular to block a nerve, e.g. mandibular nerve   block for extraction of lower molars.\n * intrathecal ( into the spinal cavity), e.g.as in cesarean section.