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 atrioventricular node lies on the right side of the partition that divides the atria, near the bottom of the right atrium. When the impulses generated by the SA node reach the AV node, they are delayed for about a tenth of a second. This delay allows the atria to contract, thereby emptying blood into the ventricles.