Sinoatrial node action potentials, so that it can pass throughout the heart and cause contraction. An action potential is a change in voltage (membrane potential) across the membrane of the cell, produced by the movement of charged atoms (ions). Non-pacemaker cells (including the ventricular and atrial cells) have a period, immediately after an action potential, where the membrane potential remains relatively constant; this is known as a resting membrane potential. This resting phase (see cardiac action potential, phase 4) ends when another action potential reaches the cell. This produces a positive change in membrane potential (known as depolarisation), which initiates the start
Sinoatrial node the 3 phases of a sinoatrial node action potential. In the ventricular action potential, there are 5 phases (labelled 0-4), however pacemaker action potentials don’t have an obvious phase 1 or 2. Phase 4 This phase is also known as the pacemaker potential. Immediately following an action potential, when the membrane potential is very negative (it is hyperpolarised) the voltage slowly begins to increase. This is initially due to the closing of potassium channels, which reduces the flow of potassium ions (I) out of the cell (see phase 3, below). Alongside the deactivation of the potassium channels, channels known as