Which type of transmembrane protein is directly responsible for maintaining the propagation of action potentials across an axon once it has been initiated?

Voltage-gated sodium channels

Explanation:

The voltage-gated sodium channels are integral membrane proteins that function to generate potential and thus propagate impulses in nerve and muscle cells. The opening of voltage-gated sodium channels produces a modification in the membrane potential through the entry of Na + ions into the cell, thereby generating an electrochemical gradient that depolarizes the cell