6th March 2024

Non-nodal cardiac potential

The non-nodal cardiac myocyte potential consists of 5 phases: 4, 0, 1, 2 and 3. Phase 4 is the resting membrane potential which sits at around -90mV. In a single action potential, there is rapid depolarisation in phase 0 due to the opening of fast sodium channels allowing Na + influx and closing of potassium channels to reduce K+ efflux. Once depolarised, the myocyte begins to repolarise with the opening of K+ ion channels, allowing for K+ efflux in phase 1. This is delayed at the plateau phase in 2 due to influx of Ca²⁺ via the L-type Ca²⁺ channels. Phase 3 follows with repolarisation due to an increase in K+ influx and a decrease in Ca2+ efflux through the closing of L-type Ca2+ channels, and the membrane potential returns to the threshold level (phase 4).