1449. The absolute refractory period of an action potential is due to _______________? September 27, 2025 by Admin A. Insufficient neurotransmitter B. Depletion of intracellular Na+ C. Inactivation of Na+ k+ ATPase D. Voltage inactivation of the Na+ channel ✅ The correct answer is option D. Voltage inactivation of the Na+ channel.