Excess potassium in the extracellular fluid has which effect on excitable membranes?

1. Potassium is the major intracellular cation and helps set the resting membrane potential. 2. In hyperkalemia potassium from the blood reaches abnormally high extracellular concentrations. 3. That flattens the normal gradient and partly depolarizes, meaning excites, the plasma membrane. 4. Skeletal muscle fibers, neurons and cardiac cells are all affected. 5. Cells then become unable to repolarize properly. 6. For the heart this means it fails to relax after contracting and stops pumping. 7. Hyperpolarization is the opposite change, and it is what low potassium produces when insulin drives potassium into cells. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 26 "Fluid, Electrolyte, and Acid-Base Balance", section Potassium_