AEMCA Practice Exam

What physical process is described as repolarization?

1. The action of sodium channels opening

2. The action of potassium channels opening and sodium channels closing

3. Movement of calcium ions into the cell

4. Inhibition of neurotransmitter release

The correct answer is: The action of potassium channels opening and sodium channels closing

Repolarization is a crucial phase in the electrical activity of a cell, particularly within the context of nerve and muscle cells during an action potential. This process involves restoring the resting membrane potential after depolarization has occurred. The correct answer describes the action of potassium channels opening while sodium channels close. During depolarization, sodium channels open and sodium ions rush into the cell, causing a decrease in the negativity of the cell's interior. Subsequently, repolarization occurs when the potassium channels open, allowing potassium ions to exit the cell. Simultaneously, the sodium channels close, preventing additional sodium from entering. This movement of potassium ions out of the cell helps to restore the internal negativity, returning the membrane potential closer to its resting state. The opening of potassium channels and closure of sodium channels are essential actions that effectively set the stage for the next cycle of action potentials, ensuring proper function in the nervous system and muscle contractions. Understanding this process is essential for comprehending the electrical activities underpinning muscle function and neuron signaling. The other choices cannot accurately capture the mechanism of repolarization in this physiological context.