An investigation was carried out to study the effects of Substance X on the transmission of nerve impulses in a myelinated motor neurone. The graph below shows the changes in membrane potential over time for a control neurone and a neurone treated with Substance X following stimulation.
Based on the experimental data, which of the following is the most likely mechanism of action of Substance X?
It blocks voltage-gated sodium channels, preventing the influx of sodium ions.
It prevents the inactivation of voltage-gated sodium channels, sustaining sodium influx.
It blocks voltage-gated potassium channels, preventing the rapid efflux of potassium ions.
It increases the rate of active transport by the sodium-potassium pump.