Use-Dependent Block: Local Anesthetics & Na⁺ Channels

This simulator models the molecular reason a local anesthetic silences a firing nerve while sparing a quiet one. A 3D axon carries ten rings of voltage-gated Na⁺ channels, each cycling through resting, open and inactivated conformations as an action potential sweeps past. The anesthetic binds every channel with a state-dependent affinity — barely at rest, far more readily once a channel opens or inactivates — so the drug preferentially traps channels that have just fired. Raise the concentration, speed up the stimulation frequency, or switch to a slower-unbinding drug and watch blocked (purple) channels accumulate ring by ring until the action potential's amplitude drops below the propagation threshold and conduction fails outright — the real basis of use-dependent, frequency-selective nerve block used in regional anesthesia.