Repolarization occurs when K + channels open and K + moves out of the axon, creating a change in electric polarity between the outside of the cell and the inside. Na + channels open at the beginning of the action potential, and Na + moves into the axon, causing depolarization. In response to a signal from another neuron, sodium- (Na +) and potassium- (K +)–gated ion channels open and close as the membrane reaches its threshold potential. As an action potential (nerve impulse) travels down an axon there is a change in electric polarity across the membrane of the axon.
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