Resting Membrane Potential

Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?

Leak Channels [Leak channels for Na+ and K+ are ubiquitous, and they allow for the diffusion of these ions across plasma membranes.]

What prevents the Na+ and K+ gradients from dissipating?

Na+-K+ ATPase [Also known as the Na+-K+ pump, or simply the pump, this transporter moves three Na+ out of the cell and two K+ into the cell for every ATP it hydrolyzes. This pumping action prevents the Na+ and K+ gradients from running down as these ions passively move through leak channels.]

Ions are unequally distributed across the plasma membrane of all cells. This ion distribution creates an electrical potential difference across the membrane. What is the name given to this potential difference?

Resting membrane potential (RMP) [The resting membrane potential is the baseline potential that can be recorded across the plasma membrane of an excitable cell prior to excitation.]

On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you?

The inside surface of the plasma membrane is much more negatively charged than the outside surface. [The inside surface of the plasma membrane accumulates more negative charge because of the presence of Na+ and K+ gradients and the selective permeability of the membrane to Na+ and K+]

The resting membrane potential depends on two factors that influence the magnitude and direction of Na+ and K+ diffusion across the plasma membrane. Identify these two factors.

The presence of concentration gradients and leak channels [he concentration gradient and the large number of K+ leak channels allow for rather robust K+ diffusion out of a cell. In contrast, the concentration gradient and the relatively few Na+ leak channels allow for much less Na+ diffusion into a cell.]

The plasma membrane is much more permeable to K+ than to Na+. Why?

There are many more K+ leak channels than Na+ leak channels in the plasma membrane. [More leak channels translates into more leakiness. Thus the outward flux of K+ is greater than the inward flux of Na+.]