10. Action potential is fired after threshold stimulus but once the nerve impulse there is the interval of time during which a second action potential cannot be initiated, no matter how large a stimulus is repeatedly applied. This interval of time is termed as
(1) Absolute refractory period
(2) Relative refractory period
(3) Threshold period
(4) Resting potential

Introduction

During nerve impulse transmission, once an action potential is generated after reaching the threshold stimulus, the neuron enters a period during which it is unable to initiate another action potential, no matter how strong the stimulus is. This time interval ensures proper signal propagation and prevention of nerve overstimulation. This article explores this critical phase, known as the absolute refractory period.

What Is the Absolute Refractory Period?

• The absolute refractory period is the phase immediately following an action potential during which the neuron cannot fire another action potential regardless of the intensity of the stimulus.

• This occurs because all voltage-gated sodium (Na⁺) channels are either already open or inactivated and require time to return to their resting closed state before reopening.

• This period overlaps the depolarization and most of the repolarization phases of the neuronal membrane.kenhub+3

• Ensures unidirectional propagation of the nerve impulse by preventing backward excitation.

Relative Refractory Period vs. Absolute Refractory Period

• Following the absolute refractory period is the relative refractory period, where a second action potential can be initiated but only by a significantly stronger-than-normal stimulus.

• The absolute refractory period guarantees discrete, separate impulses rather than continuous or overlapping signals.

Analysis of Options

Conclusion

The interval during which a second action potential cannot be initiated regardless of stimulus strength is the:

(1) Absolute refractory period