Final answer:
The opening of sodium channels results in depolarization, causing the membrane potential to move toward zero by allowing positively charged sodium ions to enter the cell.
Step-by-step explanation:
What happens to the resting membrane potential of -70 mV when sodium channels open is known as depolarization. When the sodium channels open, sodium ions (Na+) rush into the cell because of the higher concentration of sodium outside the cell relative to the inside.
This inflow of positively charged ions causes the inside of the cell to become less negative compared to the outside, moving the membrane potential toward zero. This change in voltage is the opposite of hyperpolarization, where the membrane potential becomes more negative than the resting potential, and not the same as repolarization, which returns the membrane potential back to the resting potential after depolarization.