Absolute refractory period is due to
Ans. (d) Closure of inactive gates of sodium channel(Ref: BRS physiology, Costanzo, 5th ed/p.11)Absolute refractory period:Corresponding to the period from the time the firing level is reached until repolarization is about one-third complete.No stimulus, no matter how strong, will not excite the nerve during absolute refractory periodCause - inactivation gates of the Na+ channel are closed when the membrane potential is depolarized. They remain closed until repolarization occurs. No action potential can occur, until the inactivation gates open.Relative refractory period:Begins from the remaining part of repolarization to the end of action potentialStronger than normal stimulus(suprathreshold stimulus) produces action potential in relative refractory periodCause: The K+ conductance is higher than at rest, and the membrane potential is closer to the K+ equilibrium potential and farther from threshold; therefore, more inward current is required to bring the membrane to threshold
Opening of calcium channels
Closure of potassium channels
Closure of active gates of sodium channel
Closure of inactive gates of sodium channel
Nervous System