Cardiac Muscle and Electrical Activity Quiz
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Questions and Answers

What is the purpose of this lecture?

To explain how force is produced in cardiac muscle, how it differs from skeletal muscle, and how it can be influenced by the extrinsic sympathetic nerves.

What is the difference between cardiac muscle and skeletal muscle in terms of force production?

Cardiac muscle produces force through a large influx of extracellular calcium, while skeletal muscle produces force through a smaller influx of extracellular calcium.

How do the T-tubules of cardiac muscle differ from those of skeletal muscle?

The T-tubules of cardiac muscle are 5 times greater in diameter and have 25 times more volume than those of skeletal muscle.

What is the role of dihydropyridine channels in cardiac muscle contraction?

<p>Dihydropyridine channels open in response to an action potential, allowing a large influx of extracellular calcium that contributes to cardiac muscle contraction.</p> Signup and view all the answers

How is calcium released from the sarcoplasmic reticulum in cardiac muscle?

<p>Activation of dihydropyridine channels causes release of calcium from the sarcoplasmic reticulum via ryanodine release channels.</p> Signup and view all the answers

What is the purpose of mucopolysaccharides in cardiac T-tubules?

<p>Mucopolysaccharides in cardiac T-tubules sequester calcium, ensuring its availability for contraction.</p> Signup and view all the answers

What is the topic of the lecture?

<p>Cardiac contractility and the events of the cardiac cycle.</p> Signup and view all the answers

What is the effect of the autonomic nervous system on cardiac contractility?

<p>The autonomic nervous system can influence cardiac contractility.</p> Signup and view all the answers

What is the refractory period?

<p>The refractory period is the period of time during which the cardiac muscle is unresponsive to further stimulation.</p> Signup and view all the answers

What is the purpose of volume/pressure diagrams in cardiovascular physiology?

<p>Volume/pressure diagrams are used to interpret and compare cardiac function between the left and right sides of the heart.</p> Signup and view all the answers

What is the equation for arterial pressure?

<p>Arterial pressure = cardiac output x total peripheral resistance</p> Signup and view all the answers

What is the equation for Reynolds number?

<p>Re = (velocity of flow) x (radius of vessel) / viscosity</p> Signup and view all the answers

What factors increase the likelihood of turbulence in fluid flow?

<p>High velocity flow, large diameter vessels, low blood viscosity, abnormal vessel wall</p> Signup and view all the answers

What is the effect of turbulence on flow and resistance?

<p>Turbulence disrupts flow and increases resistance</p> Signup and view all the answers

How does flow affect viscosity?

<p>Flow affects viscosity, with static blood having 100x the viscosity of flowing blood</p> Signup and view all the answers

According to LaPlace's Law, what is the relationship between distending pressure (P), opposing force or tension (T), and vessel radius (R)?

<p>T = PR</p> Signup and view all the answers

What are the practical consequences of LaPlace's Law?

<ol> <li>Control of blood flow - Low tension required to oppose blood pressure in arterioles - Smooth muscle control of arteriole and precapillary sphincters are the sites of tissue blood flow regulation</li> <li>Capillaries - Can be extremely thin and still withstand the pressure - Thin walls essential for exchange processes</li> <li>Aneurysm Regulation of blood flow</li> </ol> Signup and view all the answers

What are the three types of regulation of blood flow?

<ol> <li>Active and reactive hyperemia</li> <li>Flow autoregulation</li> <li>Myogenic response</li> </ol> Signup and view all the answers

What is the difference between active hyperemia and reactive hyperemia?

<p>Active hyperemia occurs when tissue is highly active and the rate of flow increases. Reactive hyperemia occurs when blood supply is blocked and blood flow increases to 4-7 times normal.</p> Signup and view all the answers

What are the short-term and long-term mechanisms of regulating blood flow through the microcirculation?

<p>Short-term (acute) mechanisms include vasodilator theory, which is widely accepted and involves factors such as increased PCO2, decreased PO2, increased H+, increased K+, increased lacKc acid, increased adenosine, and increased histamine. Long-term mechanisms involve changes in physical size or number of blood vessels.</p> Signup and view all the answers

What is the role of the sinoatrial node in cardiac conduction?

<p>The sinoatrial node is responsible for initiating the electrical activity in the heart, serving as the natural pacemaker.</p> Signup and view all the answers

How does depolarization spread through the heart?

<p>Depolarization spreads through the heart via a functional syncytium, starting from the atria and then moving to the ventricles.</p> Signup and view all the answers

What is the purpose of an electrocardiogram (ECG)?

<p>An electrocardiogram measures the spread of electrical activity throughout the heart and provides information about the cellular action potentials.</p> Signup and view all the answers

What is the difference between observing the electrical activity in an individual fiber versus observing the total electrical activity of the heart?

<p>Observing the electrical activity in an individual fiber provides specific information, while an ECG measures the overall electrical activity of the heart.</p> Signup and view all the answers

What is the main focus of this lecture?

<p>The main focus of this lecture is on the depolarization events in the heart.</p> Signup and view all the answers

What are the different phases of a cardiac action potential and what are the main ion channels involved in each phase?

<p>Phase 0: Rapid depolarisation due to ↑ Na+ permeability (gNa+) as fast Na+ channels open. Phase 1: Start of repolarisation as fast Na+ channels close. Phase 2: Effect of Ca2+ entry via L-type channels. Phase 3: Rapid repolarisation as ↑ [Ca2+]i stimulates K+ channels to open and gK+ ↑ Ca2+ L-type channels close. Phase 4: Stable resting membrane potential where gK+ exceeds gNa+ by 50:1.</p> Signup and view all the answers

What is the role of the autonomic nervous system in the regulation of pacemaker activity in the heart?

<p>Sympathetic stimulation increases the rate of SAN phase 1 depolarisation by ↑ gCa2+ and ↑ gNa+ via “funny” channels. Parasympathetic stimulation reduces the rate of phase 1 depolarisation and hyperpolarises the membrane potential to a lower starting level by ↑ extent and duration of opening of K+ channels, leading to an increase in gK+.</p> Signup and view all the answers

What are the electrical conduction pathways of the heart and what are their respective rates of depolarisation?

<p>Sinoatrial node (SAN): ~90/min. Atrioventricular node (AV node): ~60/min. Bundle of His: ~50/min. Purkinje fibers: ~40/min. Ventricles: ~30/min. The SAN has the fastest rate and is the intrinsic pacemaker of the heart.</p> Signup and view all the answers

How is the electrical activity of the heart measured and what information can be obtained from an electrocardiogram (ECG)?

<p>The electrical activity of the heart is measured using an electrocardiogram (ECG), which measures the electrical activity of the heart over time using multiple electrodes. The limb leads measure the sum of the electrical activity of the heart and the direction that electrical activity is moving in. The chest leads provide more specific, localized information about areas of the heart. The ECG can provide information about atrial and ventricular depolarization and repolarization, as well as the timing intervals of the P-R interval, QRS complex width, and Q-T interval.</p> Signup and view all the answers

What are the main points regarding the ionic basis for the different stages of membrane potential changes in atrial/ventricular muscle, nodal tissue, and conducting tissue throughout the heart?

<p>Many parts of the heart exhibit spontaneous, rhythmical depolarization. The electrical activity spreads in a coordinated fashion. The rate of depolarization is influenced by the autonomic nervous system. The overall net activity of the heart can be observed using an electrocardiogram (ECG).</p> Signup and view all the answers

What are the possible mechanisms of primary hypertension?

<p>Possible mechanisms of primary hypertension include the sympathetic system, the renin-angiotensin-aldosterone system (RAAS), circulating factors, and genetics.</p> Signup and view all the answers

What are the consequences of hypertension?

<p>Consequences of hypertension include increased risk of heart disease, stroke, kidney disease, and other health complications.</p> Signup and view all the answers

How is hypertension treated?

<p>Hypertension is typically treated through lifestyle changes such as diet and exercise, as well as medication if necessary.</p> Signup and view all the answers

What are the risk factors for systemic arterial hypertension?

<p>Hypertension is a complex phenotype with multiple genetic and environmental risk factors. Age, weight, sex, race, education status, and diet are all possible risk factors.</p> Signup and view all the answers

What are the possible contributors to systemic hypertension?

<p>Possible contributors to systemic hypertension include increased sympathetic activity/sensitivity, the renin-angiotensin-aldosterone system (RAAS), and circulating factors.</p> Signup and view all the answers

What is the role of the kidneys in maintaining blood pressure?

<p>The kidneys play a critical role in maintaining blood pressure by balancing sodium intake with sodium excretion, which regulates extracellular fluid (ECF) volume and long-term blood pressure. The renin-angiotensin-aldosterone system (RAAS) is also involved in regulating blood pressure.</p> Signup and view all the answers

What are the possible contributors to systemic hypertension?

<p>Increased sympathetic activity/sensitivity, renin-angiotensin-aldosterone system (RAAS), circulating factors (endothelin, nitric oxide, reactive oxygen species), and genetics.</p> Signup and view all the answers

What are the consequences of systemic hypertension?

<p>Heart failure, myocardial infarction, accelerated atherosclerosis, stroke, retinopathy, albuminuria, and end stage renal disease.</p> Signup and view all the answers

Describe the mechanisms by which the sympathetic nervous system can increase blood pressure.

<p>The sympathetic nervous system can increase blood pressure through increased sympathetic activity and sensitivity. It can directly affect blood pressure through vasoconstriction and increased contractility of cardiomyocytes. Overall, the sympathetic nervous system increases blood pressure by increasing peripheral resistance and cardiac output.</p> Signup and view all the answers

Define both primary and secondary hypertension and give a specific example of secondary hypertension.

<p>Primary hypertension refers to high blood pressure with no identifiable cause, while secondary hypertension is caused by an underlying condition or factor. An example of secondary hypertension is renal artery stenosis, which can result in decreased blood flow to the kidneys and activation of the renin-angiotensin-aldosterone system (RAAS).</p> Signup and view all the answers

What are the four broad categories of events that can lead to dysrhythmias?

<p>Heart block, Ectopic pacemaker activity, Delayed after-depolarisations, Circus re-entry</p> Signup and view all the answers

What are the common types of tachyarrhythmia?

<p>Atrial fibrillation, Supraventricular tachycardia (SVT), Ectopic beats, Sustained ventricular arrhythmias (VT and VF)</p> Signup and view all the answers

What are the three main types of dysrhythmias based on site of origin?

<p>Atrial (supraventricular), Junctional (associated with the AV node), Ventricular</p> Signup and view all the answers

What are the three types of heart block and how do they differ in terms of conduction?

<p>First degree heart block is characterized by a slightly affected AV node and slowed conduction with an abnormally long P-R interval. Second degree heart block can be further divided into several subtypes, including Mobitz type 2, which involves a constant P-R interval with occasional failure of ventricular depolarization, and 2:1 or 3:1 block, which refers to the ratio of P waves to QRS complexes. Third degree heart block is the most severe, where the AV node is completely blocked and no electrical activity from the atria reaches the ventricles.</p> Signup and view all the answers

What are ectopic pacemakers and what factors can lead to their development?

<p>Ectopic pacemakers are areas of the heart other than the sinoatrial node (SAN) that can develop pacemaker activity. They can arise due to various factors, including ischemic damage, increased sympathetic activity, increased sensitivity to catecholamines, cardiac glycoside toxicity, and other conditions like ischemia, coronary heart disease, rheumatic heart disease, hypertension, stress, exercise, caffeine consumption, hyperthyroidism, and certain medications.</p> Signup and view all the answers

What are circus re-entry movements and how do they occur in the heart?

<p>Circus re-entry movements refer to when an electrical impulse can re-stimulate a region of the heart after its refractory period has passed, creating a re-entry circuit. In the heart, this can occur when there are two branches of conducting fibers connected to a chain of contractile fibers, forming a loop. When the impulse originates in the sinoatrial node (SAN) and is transmitted to the branches, each branch depolarizes. When the impulses meet, there is extinction by collision. However, if the impulse comes from an unusual direction and arrives before the tissue would have been re-stimulated by the next normal impulse from the SAN, circus re-entry movements can occur.</p> Signup and view all the answers

What is the grey area in the context of cardiac conduction?

<p>The grey area is an area of damage with no full conduction in the orthodromic direction – cells unable to generate sufficient current to maintain the depolarisation to reach threshold at A.</p> Signup and view all the answers

What are circus re-entry movements and how are they generated?

<p>Circus re-entry movements are short circuits in the heart that result in high frequency impulses. They can be generated by either a unidirectional block or a transient block.</p> Signup and view all the answers

What is Wolf-Parkinson-White Syndrome and what are its characteristics?

<p>Wolf-Parkinson-White Syndrome is a condition characterized by an additional or &quot;accessory&quot; electrical connection between the atria and ventricles. It is usually on the left side and results in early depolarization reaching the ventricle, leading to a short PR interval and a delta wave in the QRS complex.</p> Signup and view all the answers

What is the rationale behind the Vaughn-Williams Classification system for anti-dysrhythmic drugs?

<p>The Vaughn-Williams Classification system is a classification system for anti-dysrhythmic drugs based on their mechanisms of action. It categorizes drugs into four main classes - Class I (block fast sodium channels), Class II (block beta-adrenergic receptors), Class III (prolong action potential repolarization), and Class IV (block calcium channels).</p> Signup and view all the answers

What are the two main types of dysfunction in heart failure?

<p>Systolic and diastolic dysfunction</p> Signup and view all the answers

What are the two main types of ventricular dysfunction in heart failure?

<p>Right and left ventricular dysfunction</p> Signup and view all the answers

What are the main components of afterload?

<p>Vascular resistance and ventricular wall tension</p> Signup and view all the answers

What is the equation for cardiac output?

<p>Cardiac output = HR x SV</p> Signup and view all the answers

What is the role of myocardial contractility in cardiac output?

<p>Increased contractility increases cardiac output independent of preload and afterload</p> Signup and view all the answers

What is the New York Heart Association Classification of Heart Failure?

<p>A classification system for heart failure based on patient symptoms</p> Signup and view all the answers

What are the symptoms associated with NYHA Class II heart failure?

<p>Slight limitation of physical activity. Comfortable at rest. Ordinary physical activity results in fatigue, palpitation, dyspnea (shortness of breath)</p> Signup and view all the answers

What is the classification of heart failure based on ejection fraction?

<p>Systolic vs. diastolic dysfunction</p> Signup and view all the answers

What is the main problem in systolic ventricular dysfunction?

<p>Impaired cardiac contractility</p> Signup and view all the answers

What is the main problem in diastolic ventricular dysfunction?

<p>Impaired ventricular relaxation and filling</p> Signup and view all the answers

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