Final answer:
Na+ movement through channels is primarily responsible for depolarization of an action potential. This starts the propagation of the action potential along the neuron. Subsequent repolarization and active transport restore the resting potential.
Step-by-step explanation:
Movement of Na+ through its channels is primarily responsible for the depolarization of an action potential. Depolarization occurs when the neuron receives a stimulus that makes the membrane permeable to Na+ ions. This results in Na+ ions rushing into the neuron, causing the inside of the cell membrane to become positively charged relative to the outside. This shift from the resting potential towards a more positive potential initiates the action potential. Following depolarization, repolarization occurs as the membrane becomes impermeable to Na+, and K+ ions move from high to low concentration out of the cell, restoring the negative charge on the inside of the neuron's membrane. The action potential will then propagate along the length of the axon, sequentially opening more voltage-gated Na+ channels, and continue this process of depolarization and repolarization. Finally, the sodium-potassium pump (active transport) restores the ions' concentration gradient, maintaining the cell's resting potential.