Cardiac physiology syncytium, the sinoatrial node, the atrioventricular node, the bundle of His (atrioventricular bundle), the bundle branches, and the Purkinje cells. Normal sinus rhythm is established by the sinoatrial (SA) node, the heart's pacemaker. The SA node is a specialized grouping of cardiomyocytes in the upper and back walls of the right atrium very close to the opening of the superior vena cava. The SA node has the highest rate of depolarization. This impulse spreads from its initiation in the SA node throughout the atria through specialized internodal pathways, to the atrial myocardial contractile cells and the atrioventricular node. The internodal
Orbital node moves south through the plane. In the case of objects outside the Solar System, the ascending node is the node where the orbiting secondary passes away from the observer, and the descending node is the node where it moves towards the observer. The position of the node may be used as one of a set of parameters, called "orbital elements", which describe the orbit. This is done by specifying the longitude of the ascending node (or, sometimes, the longitude of the node.) The line of nodes is the intersection of the object's orbital plane with the plane of reference. It