Question

At the molecular level, what is happening during the refactory period in neurons and muscle fibers?

Answer 1

The term “refractory period” refers to a period during the electrical activity of a cell, which can be a muscle or nerve. During refractory period, the nerve fibre does not respond to the stimuli because the sodium channels are in closed state (depolarisation ends by the closure of sodium channels, without depolarization, the impulse cannot be transmitted).

Irrespective of the intensity of the stimulus, the nerve do not accept any impulses, this period is called as absolute refractory period (the period from the peak of depolarization to the point of reaching resting membrane potential). A strong stimulus can produce action potential during relative refractory period. It immediately follows the absolute refractory period.

The refractory period of skeletal muscle is about 5 milliseconds (msec) (0.005 seconds), whereas that of the cardiac muscle is, 300 msec (0.30 sec). Means, the refractory period is longer in cardiac muscle than in the skeletal muscle.

The absolute refractory period is longer in cardiac muscle cell due to the greater plateau phase. This longer period ensures that the contraction and relaxation of cardiac muscle cells occur within a particular time frame, thus, contract in a rhythmic manner. This long absolute refractory period in cardiac cells also prevent tetanus.