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Chapter 6: Resting Membrane Potential & Action Potential

The resting membrane potential is characterized by which of the following?

A. Passive fluxes of Na+ and K+ are balanced by an active pump that derives energy from enzymatic hydrolysis of adenosine triphosphate (ATP).

B. A membrane is depolarized when the differences between the charges across the membrane are increased.

C. As the inside of the cell is made more negative with respect to the outside, the cell becomes depolarized.

D. In a cell whose membrane possesses only K+ channels, the membrane potential cannot be determined.

E. The resting membrane potential is unrelated to the separation of the charge across the membrane.

A. The potential difference across the membrane is a result of the separation charge and is called the resting membrane potential. The potential difference across the membrane is a direct function the numbers of positive and negative charges on either side of the membrane. As the separation of charge (ie, the differences between the charges) across the membrane is reduced, the membrane is said to be depolarized. Conversely, as the difference between the charges is increased, the membrane becomes hyperpolarized. In the latter case, the inside of the cell is made more negative with respect to the outside. If a cell has only a single channel in its membrane (eg, for K+), the gradients for the other become irrelevant and the membrane will approach the equilibrium potential for the single ion (K+ in this example). There is a tendency for ions to leak down their electrochemical gradients from one side of the membrane to the other. For there to be a steady resting membrane potential, the gradients across the membrane must be held constant. Changes in ionic gradients are avoided, despite the leak, by the presence of an active Na+/K+ pump (a membrane protein) that moves Na+ out of the cell and at the same time brings K+ into the cell. Such pumping mechanism requires energy because it is working against the electrochemical gradients of the 2 ions. This energy is derived from hydrolysis of ATP.

After the occurrence of an action potential, there is a repolarization of the membrane. Which of the following is the principal explanation for this event?

A. Potassium channels have been opened.

B. Sodium channels have been opened.

C. Potassium channels have been inactivated.

D. The membrane becomes impermeable to all ions.

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