MEDICAL PHYSIOLOGY

Detailed explanation-1: -The cell possesses potassium and sodium leakage channels that allow the two cations to diffuse down their concentration gradient. However, the neurons have far more potassium leakage channels than sodium leakage channels. Therefore, potassium diffuses out of the cell at a much faster rate than sodium leaks in.

Detailed explanation-2: -Since the plasma membrane at rest has a much greater permeability for K+, the resting membrane potential (-70 to-80 mV) is much closer to the equilibrium potential of K+ (-90 mV) than it is for Na+ (+65 mV).

Detailed explanation-3: -Potassium is the most important ion because the concentration of K+ is much higher in the cytosol and the cell has many K+ leakage channels. Thus K+ is able to leak outside the cell, but the other intracellular ions (proteins and phosphates), which are negatively charged, are unable to leave the cell.

Detailed explanation-4: -When the cell is at rest, some non-gated, or leak, ion channels are actually open. Significantly more potassium channels are open than sodium channels, and this makes the membrane at rest more permeable to potassium than sodium.

Detailed explanation-5: -Due to the Potassium leak channels, the plasma membrane is 50-100 times more permeable to potassium than to other positively charged ions, such as sodium. The plasma membrane is impermeable to large, intracellular negatively charged molecules such as proteins. In other words, these anions are “trapped” inside the cell.