normally due to an increased rate of expulsion of Na⁺ by the Na⁺ pump.

due solely to the movement of Cl^- ions out of the cell.

due to a delayed increase in the ratio of Na⁺ permeability to K⁺ permeability.

due to a delayed increase in Na⁺ movement across the cell membrane.

speeded up by an increased rate of K⁺ leaving the cell interior.