Sinoatrial node atrial cells, with the average cell being around 8 micrometers in diameter and 20-30 micrometers in length (1 micrometer= 0.000001 meter). Unlike the atrial cells, SA node cells contain fewer mitochondria (the power plant of the cell), fewer myofibers (the contractile machinery of the cell), and a smaller sarcoplasmic reticulum (a calcium storage organelle that releases calcium for contraction). This means that the SA node cells are less equipped to contract compared to the atrial and ventricular cells. Action potentials pass from one cardiac cell to the next through pores known as gap junctions. These gap junctions are made of
Bachmann's bundle found that clamping the muscular bundle of fibers that connects the atria caused a significant conduction delay. The Bachman's bundle receives its blood supply from the sinoatrial nodal artery (right, left or both). Besides Bachmann's bundle, the other three conduction tracts that constitute the "atrial conduction system" are known as the anterior, middle, and posterior tracts, which run from the sinoatrial node to the atrioventricular node, converging in the region near the coronary sinus. "Atrial automaticity foci" are within the atrial conduction system. The concentration of converging conduction tracts near the coronary sinus results in considerable automaticity activity originating in