![]() ![]() ![]() Therefore, there are one-half as many T tubules in cardiac muscle as in skeletal muscle. The T tubules are only found at the Z discs, whereas in skeletal muscle, they are found at the junction of the A and I bands. T (transverse) tubules penetrate from the surface plasma membrane, the sarcolemma, to the interior of the cell, allowing the electrical impulse to reach the interior. These contractile elements are virtually identical to skeletal muscle. Cardiac muscle also demonstrates striations, the alternating pattern of dark A bands and light I bands attributed to the precise arrangement of the myofilaments and fibrils that are organized in sarcomeres along the length of the cell. Structure of Cardiac MuscleĬompared to the giant cylinders of skeletal muscle, cardiac muscle cells, or cardiomyocytes, are considerably shorter with much smaller diameters. ![]() Myocardial conduction cells initiate and propagate the action potential (the electrical impulse) that travels throughout the heart and triggers the contractions that propel the blood. Their function is similar in many respects to neurons, although they are specialized muscle cells. Except for Purkinje cells, they are generally much smaller than the contractile cells and have few of the myofibrils or filaments needed for contraction. The myocardial conducting cells (1 percent of the cells) form the conduction system of the heart. Contractile cells conduct impulses and are responsible for contractions that pump blood through the body. The myocardial contractile cells constitute the bulk (99 percent) of the cells in the atria and ventricles. There are two major types of cardiac muscle cells: myocardial contractile cells and myocardial conducting cells. Even though cardiac muscle has autorhythmicity, heart rate is modulated by the endocrine and nervous systems. Neither smooth nor skeletal muscle can do this. This property is known as autorhythmicity. Not the least of these exceptional properties is its ability to initiate an electrical potential at a fixed rate that spreads rapidly from cell to cell to trigger the contractile mechanism. Recall that cardiac muscle shares a few characteristics with both skeletal muscle and smooth muscle, but it has some unique properties of its own. Identify blocks that can interrupt the cardiac cycle.Relate characteristics of an electrocardiogram to events in the cardiac cycle.Compare the effect of ion movement on membrane potential of cardiac conductive and contractile cells.Identify and describe the components of the conducting system that distributes electrical impulses through the heart.Describe the structure of cardiac muscle.Coronary angiography is indicated in patients with heart failure and anginal chest pain and should be strongly considered in patients with an electrocardiogram suggestive of ischemia or myocardial infarction.By the end of this section, you will be able to: Two-dimensional echocardiography of the heart helps differentiate systolic from diastolic dysfunction. An electrocardiograph and a chest radiograph should also be obtained. The physical examination should include Valsalva's maneuver, a test that is highly specific and sensitive for the detection of left ventricular systolic and diastolic dysfunction in patients with heart failure. It is important to determine whether the patient has had a previous cardiac event, in particular a myocardial infarction. A detailed clinical history is crucial and should address not only current signs and symptoms of heart failure but also signs and symptoms that point to a specific cause of the syndrome, such as coronary artery disease, hypertension or valvular heart disease. Although heart failure is a common clinical syndrome, especially in the elderly, its diagnosis is often missed. ![]()
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