Physiology The absolute refractory period of an action potential is due to: A Insufficient neurotransmitter B Depletion of intracellular Na+ C Inactivation of Na+ K+ ATPase D Voltage inactivation of the Na+ channel 💡 Explanation The absolute refractory period of an action potential is due to: ✓ Correct Answer: D. Voltage inactivation of the Na+ channel