Heart pump blood through the heart and into the major arteries. The pacemaker cells make up 1% of cells and form the conduction system of the heart. They are generally much smaller than the contractile cells and have few myofibrils which gives them limited contractibility. Their function is similar in many respects to neurons. Cardiac muscle tissue has autorhythmicity, the unique ability to initiate a cardiac action potential at a fixed rate – spreading the impulse rapidly from cell to cell to trigger the contraction of the entire heart. There are specific proteins expressed in cardiac muscle cells. These are mostly
Isovolumetric contraction Isovolumetric contraction In cardiac physiology, isovolumetric contraction is an event occurring in early systole during which the ventricles contract with no corresponding volume change (isovolumetrically). This short-lasting portion of the cardiac cycle takes place while all heart valves are closed. In a healthy young adult, blood enters the atria and flows to the ventricles via the opened atrioventricular valves (tricuspid and mitral valves). Atrial contraction rapidly follows, actively pumping about 20% of the returning blood. As diastole ends, the ventricles begin depolarizing and, while ventricular pressure starts to rise owing to contraction, the atrioventricular valves close in order to prevent