Exercise Physiology: Theory and Application to Fitness and Performance 9th Edition by Scott Powers, Edward Howley

Exercise 4

Define membrane potential and action potential.

Step 1 of 2

The membranes of cells are semi-permeable and selectively permeable. They allow only certain ions to pass through sparing the other. Due to this, there exists a difference in the electrical potential between the two sides of the membrane, that is, the inside of the cell and the extracellular fluid surrounding it. This difference in the electrical potential is called the membrane potential or resting membrane potential.

The membrane is more permeable to potassium ions than the sodium ions (Na⁺ and K⁺). As a result, there are more K⁺ ions inside the cell. The Na⁺/K⁺ ATPase pump actively transports Na⁺ out of the cell and K⁺ into the cell. More Na⁺ is pumped out of the cell, which leads to unequal charge distribution across the membrane. Typically, neurons have a resting potential of about -70 mV. The negative sign indicates that the cell interior is negative with respect to the extracellular fluids.