significant number of na+ ions will move into the cell down their electrochemical gradient, further depolarizing the cell. thus, the more na+ channels localized in a region of a cell's membrane the faster the action potential will propagate and the more excitable that area of the cell will be. this is an example of a positive feedback loop. the ability of these channels to assume a closed-inactivated state causes the refractory period and is critical for the propagation of action potentials down an axon. na+ channels both open and close more quickly than k+ channels, producing an influx of positive charge (na+) toward the beginning of the action potential and an efflux (k+) toward the end. ligand-gated sodium channels, on the other hand, create the change in the membrane potential in the first place, in response to the binding of a ligand to it. pharmacologic modulation blockers main article: sodium channel blocker activators