<prompt> A 56-year-old woman with severe muscle weakness is hospitalized. The only abnormality in her laboratory values is an elevated serum K concentration. The elevated serum K causes muscle weakness becauseThe Resting Membrane Potential Is HyperpolarizedThe K Equilibrium Potential Is HyperpolarizedThe Na Equilibrium Potential Is HyperpolarizedNa channels are closed by depolarization  <response>: Elevated serum K concentration causes depolarization of the K equilibrium potential and therefore depolarization of the resting membrane potential in skeletal muscle. Sustained depolarization closes the Na channels and prevents the occurrence of action potentials in the muscle. 