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 proteins called connexins. There are fewer gap junctions within the SA node and they are smaller in size. This is again important in insulating the SA node from the surrounding atrial cells. The sinoatrial node receives its blood supply from the sinoatrial nodal artery. This blood supply, however, can differ hugely between individuals. For example, in most humans this is a single artery, although in some cases there have been either 2 or 3 sinoatrial node arteries supplying the SA node. Also, the SA node artery mainly originates as a branch of the right coronary artery; however in some individuals