Normal cardiac rhythm is established by the sinoatrial (SA) node, a specialized clump of myocardial conducting cells located in the superior and posterior walls of the right atrium in close proximity to the orifice of the superior vena cava. Figure 8correlates events of heart contraction to the corresponding segments and intervals of an ECG. 
flashcard set{{course.flashcardSetCoun > 1 ? Since calcium ions cause muscles to contract, blocking calcium channels reduces contraction and increases relaxation, thus, increasing ERP. Phase 1: This phase begins once complete depolarization has occurred and the cell begins to return to its RMP.
This delay in transmission is partially attributable to the small diameter of the cells of the node, which slow the impulse. Think of it as hitting the reset button. SA nodal blocks occur within the SA node. The cardiac action potential cycle has multiple phases. Myoglobin, lipids, and glycogen are all stored within the cytoplasm. 
Cardioversion is a medical procedure that involves attaching electrical nodes to the chest to shock the heart back into its normal rhythm and increase ERP. copyright 2003-2022 Study.com. Deep entry of defibrillating effects into homogeneous cardiac tissue.
The action potential for the conductive cells consists of a prepotential phase with a slow influx of Na+ followed by a rapid influx of Ca2+ and outflux of K+. Enrolling in a course lets you earn progress by passing quizzes and exams. This is also considered the. In a 12-lead ECG, six electrodes are placed on the chest, and four electrodes are placed on the limbs. Despite this initial difference, the other components of their action potentials are virtually identical. The sarcolemmas from adjacent cells bind together at the intercalated discs. Figure 4. (Micrograph provided by the Regents of the University of Michigan Medical School 2012). This establishes the typical maximum heart rate in a healthy young individual. She has also worked as an ocean & Earth science educator. Other causes are more difficult to correct. Since the left ventricle is much larger than the right, the left bundle branch is also considerably larger than the right. The resulting movement of sodium ions creates spontaneous depolarization (or prepotential depolarization). The https:// ensures that you are connecting to the Contractile cells conduct impulses and are responsible for contractions that pump blood through the body. A refractory period follows, during which concentration of K+and Na+are actively restored to their appropriate sides of the sarcolemma by Na+/K+pumps. The heart's atrium (upper chambers) and ventricles (lower chambers) have their own ERP, with atrial ERP being much shorter than ventricular ERP. endstream endobj 295 0 obj <>/Metadata 32 0 R/Pages 292 0 R/StructTreeRoot 52 0 R/Type/Catalog>> endobj 296 0 obj <>/MediaBox[0 0 612 792]/Parent 292 0 R/Resources<>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI]/XObject<>>>/Rotate 0/StructParents 0/Tabs/S/Type/Page>> endobj 297 0 obj <>stream Careful analysis of the ECG reveals a detailed picture of both normal and abnormal heart function, and is an indispensable clinical diagnostic tool. With extreme stimulation by the SA node, the AV node can transmit impulses maximally at 220 per minute. (Seek additional content for more detail about metabolism.). Their influx through slow calcium channels accounts for the prolonged plateau phase and absolute refractory period that enable cardiac muscle to function properly. Intervals include one segment plus one or more waves. Note the lack of a resting potential. If decreased ERP is caused by a medication, stopping or changing the medication will help. - Definition, Causes & Symptoms, What Is CPR?
This also would cause problems, which we will discuss later. Some devices also contain built-in defibrillators. Additionally, it will not reveal the effectiveness of the pumping, which requires further testing, such as an ultrasound test called an echocardiogram or nuclear medicine imaging. The effective refractory period (ERP) and the absolute refractory period (ARP) are two varieties of cardiac refractory periods. Since the SA node is the pacemaker, it reaches threshold faster than any other component of the conduction system. Refractory periods are resting periods where the heart cannot produce another action potential. The conductive cells within the heart establish the heart rate and transmit it through the myocardium. The electrical event, the wave of depolarization, is the trigger for muscular contraction. 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. (a) An external automatic defibrillator can be used by nonmedical personnel to reestablish a normal sinus rhythm in a person with fibrillation. Therefore, there are one-half as many T tubules in cardiac muscle as in skeletal muscle. 
The SA node, without nervous or endocrine control, would initiate a heart impulse approximately 80100 times per minute. The SA node has the highest inherent rate of depolarization and is known as the pacemaker of the heart. Sodium channels become inactive, which is why another action potential is not triggered. It is generally agreed that inhomogeneities of the recovery process in cardiac tissue play an important role in the genesis of reentrant arrhythmias. The influx or outflux of ions always creates the voltage difference. Additionally, the absolute refractory period (ARP) involves a part of the ERP where it is absolutely impossible to stimulate an action potential. The simulations suggest that discrete effects of junctional resistance may be involved in fibrillation and defibrillation. - Definition, Symptoms & Causes, What Is Hypotension? During the ERP, however, a very strong stimulus might work, but only during the end of Phase 3. Its like a teacher waved a magic wand and did the work for me. The Immune System and Other Body Defenses, Chemical Reactions in Metabolic Processes, Quiz: Chemical Reactions in Metabolic Processes, Connective Tissue Associated with Muscle Tissue, Quiz: Connective Tissue Associated with Muscle Tissue, Quiz: Structure of Cardiac and Smooth Muscle, Muscle Size and Arrangement of Muscle Fascicles, Quiz: Muscle Size and Arrangement of Muscle Fascicles, Quiz: The Ventricles and Cerebrospinal Fluid, Quiz: The Hypothalamus and Pituitary Glands, Quiz: Functions of the Cardiovascular System, Quiz: Specific Defense (The Immune System), Humoral and Cell-Mediated Immune Responses, Quiz: Humoral and Cell-Mediated Immune Responses, Quiz: Structure of the Respiratory System, Quiz: Structure of the Digestive Tract Wall, Online Quizzes for CliffsNotes Anatomy and Physiology QuickReview, 2nd Edition. Alternans and the influence of ionic channel modifications: Cardiac three-dimensional simulations and one-dimensional numerical bifurcation analysis. These changes are usually caused by shortening of the ERP. In the event of a heart attack or MI, dead cells are often replaced by patches of scar tissue. Conductive cells contain a series of sodium ion channels that allow a normal and slow influx of sodium ions that causes the membrane potential to rise slowly from an initial value of 60 mV up to about 40 mV. It is impossible to stimulate an action potential during this period as the voltage-gated Na+ channels are inactivated and cannot be opened. I would definitely recommend Study.com to my colleagues. Bundle branch blocks occur within either the left or right atrioventricular bundle branches. Approximately 20 percent of the calcium required for contraction is supplied by the influx of Ca2+ during the plateau phase. The entire event lasts between 250 and 300 ms (Figure 5). There are five prominent points on the ECG: the P wave, the QRS complex, and the T wave.
The absolute refractory period for cardiac contractile muscle lasts approximately 200 ms, and the relative refractory period lasts approximately 50 ms, for a total of 250 ms. A fully developed adult heart maintains the capability of generating its own electrical impulse, triggered by the fastest cells, as part of the cardiac conduction system. Segments are defined as the regions between two waves. c AW\eu?. The .gov means its official. Oxygen from the lungs is brought to the heart, and every other organ, attached to the hemoglobin molecules within the erythrocytes. Although ERP and ARP may seem similar, their slight difference has to do with inactivated Na+ channels. artificial pacemaker:medical device that transmits electrical signals to the heart to ensure that it contracts and pumps blood to the body, atrioventricular bundle:(also, bundle of His) group of specialized myocardial conductile cells that transmit the impulse from the AV node through the interventricular septum; form the left and right atrioventricular bundle branches, atrioventricular bundle branches:(also, left or right bundle branches) specialized myocardial conductile cells that arise from the bifurcation of the atrioventricular bundle and pass through the interventricular septum; lead to the Purkinje fibers and also to the right papillary muscle via the moderator band, atrioventricular (AV) node:clump of myocardial cells located in the inferior portion of the right atrium within the atrioventricular septum; receives the impulse from the SA node, pauses, and then transmits it into specialized conducting cells within the interventricular septum, autorhythmicity:ability of cardiac muscle to initiate its own electrical impulse that triggers the mechanical contraction that pumps blood at a fixed pace without nervous or endocrine control, Bachmanns bundle:(also, interatrial band) group of specialized conducting cells that transmit the impulse directly from the SA node in the right atrium to the left atrium, bundle of His:(also, atrioventricular bundle) group of specialized myocardial conductile cells that transmit the impulse from the AV node through the interventricular septum; form the left and right atrioventricular bundle branches, electrocardiogram (ECG):surface recording of the electrical activity of the heart that can be used for diagnosis of irregular heart function; also abbreviated as EKG, heart block:interruption in the normal conduction pathway, interatrial band:(also, Bachmanns bundle) group of specialized conducting cells that transmit the impulse directly from the SA node in the right atrium to the left atrium, intercalated disc:physical junction between adjacent cardiac muscle cells; consisting of desmosomes, specialized linking proteoglycans, and gap junctions that allow passage of ions between the two cells, internodal pathways:specialized conductile cells within the atria that transmit the impulse from the SA node throughout the myocardial cells of the atrium and to the AV node, myocardial conducting cells:specialized cells that transmit electrical impulses throughout the heart and trigger contraction by the myocardial contractile cells, myocardial contractile cells:bulk of the cardiac muscle cells in the atria and ventricles that conduct impulses and contract to propel blood, P wave:component of the electrocardiogram that represents the depolarization of the atria, pacemaker:cluster of specialized myocardial cells known as the SA node that initiates the sinus rhythm, prepotential depolarization:(also, spontaneous depolarization) mechanism that accounts for the autorhythmic property of cardiac muscle; the membrane potential increases as sodium ions diffuse through the always-open sodium ion channels and causes the electrical potential to rise, Purkinje fibers:specialized myocardial conduction fibers that arise from the bundle branches and spread the impulse to the myocardial contraction fibers of the ventricles, QRS complex:component of the electrocardiogram that represents the depolarization of the ventricles and includes, as a component, the repolarization of the atria, sinoatrial (SA) node:known as the pacemaker, a specialized clump of myocardial conducting cells located in the superior portion of the right atrium that has the highest inherent rate of depolarization that then spreads throughout the heart, sinus rhythm:normal contractile pattern of the heart, spontaneous depolarization:(also, prepotential depolarization) the mechanism that accounts for the autorhythmic property of cardiac muscle; the membrane potential increases as sodium ions diffuse through the always-open sodium ion channels and causes the electrical potential to rise, T wave:component of the electrocardiogram that represents the repolarization of the ventricles, http://cnx.org/contents/14fb4ad7-39a1-4eee-ab6e-3ef2482e3e22@8.25, 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.
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