Nucleic acids Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are made up of nucleic acids found in the nuclei of living cells.They are the vehicles of genetic inheritance. Nucleic acids are condensation polymers of nucleotides.ucleic acids Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are made up of nucleic acids found in the nuclei of living cells.
After the ventricles complete their contraction phase, they relax and the SA node initiates another impulse to start another cardiac cycle. The Heart: Conduction System The heart pumps blood through the body This is accomplished by contraction and relaxation of the cardiac muscle tissue in the myocardium layer.
There are two types of cardiac myocytes (or cardiomyocytes): contractile cells and conducting cells. The contractile myocytes form the bulk of the heart wall. They are striated muscle cells (not very different from the muscles in the rest of the body that allow us to move). The conducting cells form the sinoatrial (SA) node, the atrioventricular (AV) node, the bundle of His and the Purkinje system. These cells regulate the automatic contractility of the heart. The SA node is the source of initial impulses and is responsible for the normal rhythm of the heart (called the 'sinus rhythm').