Final answer:
Neuron depolarization occurs when voltage-gated Na+ channels open and Na+ ions enter the cell, reversing the polarity of the membrane and triggering an action potential that travels down the axon.
Step-by-step explanation:
When a neuron depolarizes, the process begins with the opening of voltage-gated Na+ (sodium) channels, allowing positive sodium ions to rush into the cell. This rapid influx of Na+ ions reverses the polarity of the cell's membrane, changing the voltage from approximately -70mV to +30mV, a state known as depolarization. Following this, voltage-gated K+ (potassium) channels open, and K+ ions begin to leave the cell, repolarizing it. As K+ exits, Na+ channels become inactivated, preventing further entry of sodium ions. Eventually, the efflux of K+ ions overshoots, leading to hyperpolarization of the neuron. The action potential, the pulse of voltage inside a nerve cell, travels down the axon as a wave, promoting the sequential opening and closing of Na+ and K+ channels.