How does a regional nerve block numb a limb?

A regional nerve block numbs a limb by injecting a local anesthetic near a main nerve trunk, which temporarily interrupts the transmission of nerve impulses along both sensory and motor nerve fibers.1

The process works at the cellular level:
* Mechanism of Action: The anesthetic molecules penetrate the fatty membrane of the nerve fibers and block ion channels from the inside.1
* Blocking Conduction: By preventing the influx of sodium ions through these channels, the drug stops the small electrical currents necessary to transport impulses along the nerve.1
* Result: Because the nerve trunk is blocked, the brain no longer receives pain signals from the limb, and motor commands are prevented from reaching the periphery, allowing surgical procedures to be performed while the patient remains conscious.1

The duration of this effect is determined by how quickly the body disperses, metabolizes, and excretes the drug. Sometimes, epinephrine is added to the solution to narrow blood vessels, which slows the drug's dispersal and prolongs the anesthesia.1