Question

During an action potential, the rapid decrease in sodium ion permeability and the simultaneous and rapid increase in potassium ion permeability is responsible for __________.

Answer 1

The answer is: the repolarization of the cell.
Muscle and nerve cells use action potentials to communicate and send signals. Nerve cells have a resting membrane potential which is a negative concentration gradient, meaning that there are more positively charged ions outside the cell compared to the inside of the cell. These positively charged ions are sodium ions, therefore, there are more sodium ions outside the cell and more potassium ions inside the cell. Repolarization of the cell is a process that happens during action potential and it comes after the depolarization of the membrane. During repolarization, the membrane potential changes and returns to the negative value of the resting potential. At this phase, the sodium channels close and the potassium channels open, causing the nerve cell to lose positively charged ions.

Answer 2

The answer is repolarization. In the first phases of an action potential,
Sodium ions flow into the cell, through the voltage-gated ion channels, causing depolarization from the resting potential of -70 mV. In the later stages of the action potential, the potassium ion selective filter channels open and potassium ions move from inside of the cell to the outside. This repolarizes the cell before sodium ions begin to be pumped out of the cell.