Please help answer this question ONLY if you are an expert on the subject. Pleas

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Please help answer this question ONLY if you are an expert on the subject. Please clearly explain. Thank you.

Animal physiology question: When membrane potential changes, we use the terms depolarization, hyperpolarization, and repolarization. Explain what is happening to the membrane potential in relation to the extracellular fluid during depolarization and hyperpolarization. Explain how depolarization is possible with the movement of either positive or negative ions. Explain how hyperpolarization is possible with the movement of either positive or negative ions.

Explanation / Answer

Answer

The cell membrane at resting stage maintains specific ion concentration. The concentration makes membrane potential of -70 mV. At this point, the inside cell is more negative due to more negative ions and also consist more potassium ions inside the cell and the outside cell is the more positive due presence of more sodium ions. The cells are always poor in sodium. During resting ions are at equilibrium.

If apply the membrane potential changes, After the threshold potential, the membrane opens the fast sodium channels and causes an influx of sodium ions and membrane potential moves to more positive up to +30 mV. This is called depolarization.

In the second step, the sodium channels are closed and the opening of potassium channels occurs and causes efflux of ions that results in positive charge inside cell slowly drops. This is called Repolarization. The potassium channels are open up to membrane potential and the membrane potential is restored to -70 mV.

The potassium channels are slowly closing and this cause the membrane to more negative membrane potential may be more than -90 mV. This is called hyperpolarization.

After that, the voltage-gated potassium channels closed and the membrane potential returns to resting membrane potential -7mV. The most of voltage-gated channels do not exhibit inactivate so returns to resting membrane and ready for next action potential.

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