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.
Each electrical signal normally begins in a group of cells called the sinus node or sinoatrial (SA) node. As a signal spreads from the top of the heart to the bottom, it coordinates the timing of heart cell activity. First, the heart's two upper chambers, the atria (AY-tree-uh), contract. This contraction pumps blood into the heart's two lower chambers, the ventricles (VEN-trih-kuls). The ventricles then contract and pump blood to the rest of the body. The combined contraction of the atria and ventricles is a heartbeat.