Question

All of the following are true about the refractory period in cardiac muscle, except

A.		it results from the plateau phase of the action potential.
B.		it is much longer than the refractory period in skeletal muscle.
C.		it is observed in both contractile and autorhythmic cardiocytes.
D.		it prevents complete tetanus.
E.		it prolongs the action potential until the muscle cell has begun to relax.

Answer 1

Ans - it is observed in both contractile and autorhythmic cardiocyte

In cardiac muscle cells , There are absolute and relative refractory periods .

Absolute refractory period: is a period during which the cardiac excitability is totally cancelled i.e. cardiac muscle will not respond to any stimulus . It prologs from the beginning of the depolarization phase till the end of plateau phase ( about 250 -300 ms ) about hundred times longer that of the skeletal muscle`s refractory period and due to this absolute refractory period tetanisation of cardiac muscle is impossible

Relative refractory period : is a period that follows the absolute period , and the excitability begins to recover gradually until it reaches its normal value. Relative refractory period coincides with the period of rapid polarization following the plateau.