The unique regular hexahedron is the cube, and there are two hexahedra that can be built from regular polygons with equal edge lengths: the regular triangular dipyramid the pentagonal pyramid. Through graph duality, the list of numbers of vertices for each polyhedron in a hexahedron corresponds to the degree sequence (sequence of vertex degrees) of a hexahedral graph. The following table lists the hexahedra, together with their degree sequences, number of vertices , and number of edges , which are related through the polyhedral formula.
The atrioventricular (AV) node is a part of the electrical conduction system of the heart that coordinates the top of the heart.It electrically connects atrial and ventricular chambers.he AV node is an area of specialized tissue between the atria and the ventricles of the heart, specifically in the posteroinferior region of the interatrial septum near the opening of the coronary sinus, which conducts the normal electrical impulse from the atria to the ventricles.
The heart actually has two natural pacemakers. The sinoatrial node (SA node) is the primary pacemaker and the atrioventricular node (AV node) is the secondary. The AV node is in a bundle of tissues on the border that separates the right atrium and the right ventricle. When the SA node sends out an electrical impulse, it goes straight to the AV node.