If potassium channels are blocked, what would the membrane fail to do, extending the length of the action potential and stimulating excessive muscle contractions?

When potassium channels are blocked, the membrane's ability to repolarize following an action potential is compromised. During an action potential, depolarization occurs when sodium channels open, allowing sodium ions to flow into the cell. This is followed by repolarization, where potassium channels open to allow potassium ions to exit the cell, leading to a return to a more negative membrane potential.

If potassium channels are blocked, potassium cannot flow out of the cell as it normally would during the repolarization phase. Consequently, this failure to repolarize results in prolonged depolarization, which extends the duration of the action potential. This can lead to excessive and sustained muscle contractions, known as tetanus, because the muscle fibers are unable to relax appropriately between stimulation events.

In summary, the blockage of potassium channels specifically prevents the process of repolarization from occurring, prolonging the action potential and potentially leading to excessive muscle contraction.