Which of the following events is NOT a characteristic of an action potential?a. The plasma membrane becomes highly permeable to sodium ions and depolarization results.b. As sodium ions enter, the inside of the plasma membrane becomes more negative.c. At the peak of depolarization, sodium channels begin to close and potassium channels open.d. In repolarization, potassium ions flow out of the cell.e. Action potentials occur according to the all-or-none principle.
As sodium ions enter, the inside of the plasma membrane becomes more negative.
The correct answer is option b. As sodium ions enter, the inside of the plasma membrane becomes more negative.
Explanation:
An action potential is a rapid and reversible change in the membrane potential of a neuron or muscle cell that propagates as a wave along the cell membrane. It is characterized by the following events:
a. The plasma membrane becomes highly permeable to sodium ions and depolarization results. This occurs when the threshold potential is reached, and voltage-gated sodium channels open, allowing sodium ions to rush into the cell.
b. As sodium ions enter, the inside of the plasma membrane becomes more positive (not negative). This is because sodium ions carry a positive charge and their entry into the cell causes depolarization (i.e., the membrane potential becomes less negative or more positive).
c. At the peak of depolarization, sodium channels begin to close, and potassium channels open. This causes the membrane potential to repolarize (i.e., become more negative again).
d. In repolarization, potassium ions flow out of the cell. This is because potassium channels open, allowing the positively charged potassium ions to move out of the cell, thereby restoring the negative charge inside the cell.
e. Action potentials occur according to the all-or-none principle. This means that once the threshold potential is reached, an action potential will occur with the same amplitude and duration every time, regardless of the stimulus strength that initiated it.
Therefore, option b is not a characteristic of an action potential as it states that the inside of the plasma membrane becomes more negative, which is the opposite of what happens during the depolarization phase of an action potential.
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