Question

In a patient exhibiting a mild hyperkalemic state, explain why:

1. the resting membrane potential of neurons would rise closer to threshold
2. why the repolarization phase of an action potential will take much longer than when a person is in a normokalemic state.

Answer 1

Mild hyperkalemia can cause the resting membrane potential of neurons to rise closer to the threshold due to higher extracellular K+ levels, making it easier to trigger an action potential. The repolarization phase is prolonged because the efflux of K+ is slowed down, due to the decreased gradient between the intracellular and extracellular K+ concentrations.

Step-by-step explanation:

In a patient with mild hyperkalemia, the resting membrane potential of neurons is affected because of the concentration gradient changes for K+. Hyperkalemia means there is a higher concentration of K+ outside the cell, causing the cell to be less negative and thus closer to the threshold for depolarization. This makes neurons more excitable and an action potential may be initiated with a smaller stimulus than usual.

The repolarization phase of an action potential takes much longer in hyperkalemia because K+ efflux is slowed. During repolarization, K+ ions flow out of the cell to restore the negative membrane potential. However, with increased extracellular K+, the gradient is reduced, and thus the exit of K+ ions during repolarization is lessened, prolonging the phase.