As a domain expert in cellular physiology, I can explain the process of depolarization in the context of an action potential in neurons or muscle cells.

During the depolarization phase of an action potential, certain types of ion channels in the cell membrane open and close in a coordinated manner. The primary ions involved in this process are sodium (Na+) and potassium (K+).


1. Opening of Sodium Channels: Initially, voltage-gated sodium channels open in response to a stimulus that causes the membrane potential to become less negative (depolarize). This opening allows sodium ions to flow into the cell down their concentration gradient, which further depolarizes the membrane.


2. Closing of Sodium Channels: After a brief period, these sodium channels begin to close. This closure prevents further influx of sodium ions.


3. Opening of Potassium Channels: As sodium channels close, voltage-gated potassium channels begin to open. This allows potassium ions to flow out of the cell, which starts to repolarize the membrane, returning it toward its resting state.


4. Closing of Potassium Channels: Eventually, the potassium channels also close, and the sodium-potassium pump (an active transport mechanism) works to restore the resting membrane potential by pumping sodium ions out of the cell and potassium ions into the cell.

The entire process is rapid and self-propagating, allowing the action potential to travel along the length of the neuron or muscle cell.

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After a cell has been depolarized, it undergoes one final change in internal charge. Following depolarization, the voltage-gated sodium ion channels that had been open while the cell was undergoing depolarization close again. The increased positive charge within the cell now causes the potassium channels to open.read more >>