Final answer:
When Na+ ions leak down its concentration gradient, they enter the cell even after the membrane potential becomes zero. This process, known as depolarization, leads to the membrane potential moving toward zero and plays a role in generating an action potential in cells.
Step-by-step explanation:
When Na+ ions are allowed to leak down its concentration gradient, they will continue to enter the cell even after the membrane potential has become zero. This is because the concentration gradient for Na+ is so strong. As sodium ions enter the cell, the voltage immediately around the pore becomes positive, reaching +30 mV by the time all the sodium has entered the cell.
This process is known as depolarization, where the membrane potential moves toward zero. It is a key step in generating an action potential in cells.
The electrical gradient, along with the concentration gradient, plays a role in attracting sodium ions into the cell. The negative proteins below the membrane attract the positively charged sodium ions.