Describe how contractile cells are able to contract rapidly but are not likely to experience tetanus. Include the following terms in your answer : refractory period, calcium channels, contraction period, relaxation period, depolarization, and repolarization

Question

What will be an ideal response?

Answer 1

When a contractile cell is brought to threshold, its voltage-gated Na+ channels open, causing the membrane potential to reverse. At the peak of the depolarization, the Na+ channels close and then voltage-gated K+ channels open and the membrane begins to repolarize. However, slow calcium channels then open and prolong the depolarized condition as Ca2+ ions rush into the cell, thereby counteracting the repolarization occurring as K+ ions are flowing out of the cell. In a short while, the Ca2+ channels close but the K+ remains open. Repolarization then proceeds and brings the membrane potential back to the repolarized condition. This relatively long refractory period (when the membrane is depolarized and not capable of responding to another stimulus) is about as long as the contraction period for the muscle cell. Therefore, the cell is able to relax before it can respond to another stimulus and begin a subsequent contraction.