Peripheral Nerves and Local Anesthesia Quiz

Classification of Nerve Fibers and Factors Affecting Local Anesthetic Action

• Peripheral nerves are classified based on electrophysiological and morphological differences.
• Type A fibers are further divided into four groups, responsible for motor action, muscle proprioception, fast sharp pain, temperatures, touch, and pressure.
• Type B fibers are preganglionic and responsible for sympathetic activity.
• Type C fibers are unmyelinated and responsible for conduction of dull or burning pain.
• Local anesthetics (LA) prevent both the generation and conduction of a nerve impulse, acting like a roadblock between the source of impulse and the brain.
• The nerve membrane is the site where LA agents exert their pharmacological actions, and popular theories include the membrane expansion theory and specific receptor theory.
• The pH value of a local anesthetic solution greatly influences its action, and acidification of tissue decreases its effectiveness.
• Inadequate anesthesia results when local anesthetics are injected into inflamed or infected areas.
• Increased lipid solubility of local anesthetics permits the anesthetic to penetrate the nerve membrane more easily.
• The degree of protein binding of the anesthetic molecule is responsible for the duration of local anesthetic activity.
• The local anesthetic solution with greater vasodilator activity will increase blood flow to the area and decrease anesthetic potency and duration.
• The duration is increased in areas of decreased vascularity.