This presentation is appropriate for reference but, in the interactive classroom the promotion of understanding through clear, concise visual cues is essential 1.
By the end of this section, you will be able to: Describe the structure of cardiac muscle Identify and describe the components of the conducting system that distributes electrical impulses through the heart Compare the effect of ion movement on membrane potential of cardiac conductive and contractile cells Relate characteristics of an electrocardiogram to events in the cardiac cycle Identify blocks that can interrupt the cardiac cycle Recall that cardiac muscle shares a few characteristics with both skeletal muscle and smooth muscle, but it has some unique properties of its own.
Contractions of the heart heartbeats are controlled by specialized cardiac muscle cells called pacemaker cells that directly control heart rate. This property is known as autorhythmicity.
Neither smooth nor skeletal muscle can do this. Although cardiac muscle cannot be consciously controlled, the pacemaker cells respond to signals from the autonomic nervous system ANS to speed up or slow down the heart rate.
The pacemaker cells can also respond to various hormones that modulate heart rate to control blood pressure. There are two major types of cardiac muscle cells: The myocardial contractile cells constitute the bulk 99 percent of the cells in the atria and ventricles.
Contractile cells conduct impulses and are responsible for contractions that pump blood through the body. The myocardial conducting cells 1 percent of the cells are the autorhythmic cells and form the conduction system of the heart. Except for Purkinje cells, they are generally much smaller than the contractile cells and have few of the myofibrils or filaments needed for contraction.
Their function is similar in many respects to neurons, although they are specialized muscle cells.
Structure of Cardiac Muscle Compared to the giant cylinders of skeletal muscle, cardiac muscle cells, or cardiomyocytes, are considerably shorter with much smaller diameters. 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 Figure These contractile elements are virtually identical to skeletal muscle.
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. 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.
Therefore, there are one-half as many T tubules in cardiac muscle as in skeletal muscle. In addition, the sarcoplasmic reticulum stores few calcium ions, so most of the calcium ions must come from outside the cells. The result is a slower onset of contraction. Mitochondria are plentiful, providing energy for the contractions of the heart.
Typically, cardiomyocytes have a single, central nucleus, but two or more nuclei may be found in some cells. Cardiac muscle cells branch freely.
A junction between two adjoining cells is marked by a critical structure called an intercalated disc, which helps support the synchronized contraction of the muscle Figure The sarcolemmas from adjacent cells bind together at the intercalated discs.Calcium ions play two critical roles in the physiology of cardiac muscle.
Their influx through slow calcium channels accounts for the prolonged plateau phase and absolute refractory period that enable cardiac muscle to function properly. Cardiac Valve Disease.
Coronary Artery Disease. Edema. Heart Failure. Hypertension. Click here for information on Cardiovascular Physiology Concepts, 2nd edition, a textbook published by Lippincott Williams & Wilkins () Click here for information on Normal and Abnormal The recorded tracing is called an electrocardiogram (ECG, or EKG.
Understanding the basis of a normal ECG requires appreciation of four phe-nomena: the electrophysiology of a single cell, how the wave of electrical current propagates through myocardium, the physiology of the specific structures of the heart through which the electrical wave travels, and last how that leads to a mea- Cardiac potentials may.
Apr 30, · By , the importance of electrocardiogram in differentiating cardiac from non-cardiac chest pain was well recognized; in fact, some patterns were considered so characteristic that the electrocardiogram alone could be used to confirm the diagnosis of myocardial infarction.
Physiology Cardiac output (CO) Amount of blood pumped by the left ventricle in one minute Normal cardiac output is 4 – 8 L/min Cardiac Output = Stroke Volume x Heart Rate **Our Swan boxes give us a continuous cardiac output reading!
Physiology Pre-load. Understanding the basic anatomy and physiology of the human body The cardiovascular system It transports oxygen, carbon dioxide, waste products, nutrients and .