Final answer:
The depolarization phase is primarily produced by the movement of sodium (Na+) ions into the axon. This influx of Na+ through voltage-gated channels causes the membrane potential to become positive, which is a critical step in the propagation of an action potential along a neuron.
Step-by-step explanation:
The depolarization phase of the action potential is primarily produced by the movement of sodium (Na+) ions into the axon. During this phase, a stimulus triggers the voltage-gated Na+ channels to open, allowing Na+ to enter the cell rapidly, which causes the inside of the cell membrane to become more positive. This change in electrical charge across the membrane is critical for conducting a nerve impulse down the length of the axon, which is an essential process for neural communication.
Propagation of the action potential involves these Na+ ions entering through open channels and moving along the inside of the cell membrane. The entry of Na+ causes the adjacent areas of the cell membrane to depolarize, which in turn opens more voltage-gated Na+ channels further along the axon, creating a wave-like spread of depolarization. This mechanism ensures that the action potential travels in one direction toward the axon terminals.
After depolarization, repolarization occurs when voltage-gated K+ channels open allowing potassium (K+) ions to move out of the cell, bringing the membrane potential back toward the resting level. Following this, the sodium-potassium pump helps to restore the resting potential by actively transporting Na+ out of the cell and K+ back into the cell.