The propagation of an action potential along a nerve fiber is caused by the opening of voltage-gated [[1]] and potassium channels.

The propagation of an action potential along a nerve fiber is caused by the opening of voltage-gated sodium (Na+) and potassium (K+) channels.

During an action potential, the opening of voltage-gated sodium channels at the initial segment of the axon membrane leads to a rapid influx of Na+ ions into the neuron, causing depolarization of the membrane potential. This depolarization then triggers the opening of voltage-gated potassium channels, which allow K+ ions to flow out of the neuron and repolarize the membrane potential. The efflux of K+ ions also helps to restore the resting membrane potential by hyperpolarizing the neuron.

As the action potential travels down the axon, it causes a wave of depolarization and repolarization that propagates along the length of the neuron. This is due to the opening of voltage-gated sodium and potassium channels at each segment of the axon membrane as the action potential moves forward. The opening of these channels is triggered by changes in the membrane potential that result from the influx of sodium ions at the previous segment of the axon. This process continues until the action potential reaches the end of the axon, where it triggers the release of neurotransmitters into the synapse to communicate with other neurons or target cells.