Cardiac Muscle Cells Physiology

-90 mV; fast voltage-gated Na+ channels, voltage-gated K+ channels, and slow voltage-gated Ca2+ channels are involved.

The exit of K+ and the entry of Ca2+ balance each other, resulting in no net electrical change at the sarcolemma.

The phases are depolarization, plateau, and repolarization; they are essential for the rhythmic contraction and relaxation of cardiac muscles.

<p>The opening of fast voltage-gated Na+ channels initiates depolarization, changing the membrane potential to +30 mV.</p> Signup and view all the answers

<p>Slow voltage-gated Ca2+ channels open, allowing Ca2+ to enter the cell while K+ exits, leading to the membrane potential leveling off.</p> Signup and view all the answers

<p>The entrance of Ca2+ into the cell during depolarization triggers the release of more Ca2+ from the sarcoplasmic reticulum.</p> Signup and view all the answers

<p>It causes a conformational change that allows actin and myosin filaments to slide past each other, resulting in contraction.</p> Signup and view all the answers

<p>It triggers the release of further Ca2+ from the SR and initiates muscle contraction, essential for effective heart function.</p> Signup and view all the answers

<p>The depolarization is caused by the rapid entry of Na+ ions through fast voltage-gated Na+ channels, changing the membrane potential from -90 mV to +30 mV.</p> Signup and view all the answers

<p>The plateau phase maintains the membrane potential at +30 mV for a short period, allowing a prolonged contraction that increases the force of the cardiac muscle contraction.</p> Signup and view all the answers

<p>Slow voltage-gated Ca2+ channels open during the plateau phase, allowing Ca2+ ions to enter the cell, which sustains the depolarized state.</p> Signup and view all the answers

<p>Repolarization occurs when voltage-gated K+ channels open, allowing K+ to flow out of the cell, returning the membrane potential back to -90 mV.</p> Signup and view all the answers

<p>The refractory period is the time during which the cardiac muscle cell cannot respond to a new action potential, ensuring that the heart contracts effectively without premature re-excitation.</p> Signup and view all the answers

<p>Ca2+ channel blockers decrease the entry of Ca2+ into cardiac muscle cells, leading to a reduction in the force of contraction and a slower heart rate.</p> Signup and view all the answers

<p>Crossbridge cycling involves the formation of crossbridges between myosin and actin, followed by a powerstroke that pulls the thin filament, and the release and reset of the myosin head using ATP.</p> Signup and view all the answers

<p>Cardiac muscle contraction is initiated by the entry of Ca2+ into the sarcoplasm, where calcium binds to troponin to start the crossbridge cycling process.</p> Signup and view all the answers

<p>EDV indicates the maximum blood volume that the ventricles can hold at the end of diastole, approximately 130 mL in a resting adult.</p> Signup and view all the answers

<p>During isovolumic contraction, the ventricles contract with no change in blood volume as the AV valves close and semilunar valves remain closed.</p> Signup and view all the answers

<p>Pressure changes drive the opening and closing of heart valves; higher pressure in the atria opens the AV valves for ventricular filling.</p> Signup and view all the answers

<p>The semilunar valves open to allow blood to be ejected from the ventricles into the arterial trunks as ventricular pressure exceeds arterial pressure.</p> Signup and view all the answers

<p>Stroke volume (SV) is the volume of blood pumped out of the ventricles during each contraction, approximately 70 mL in a healthy adult.</p> Signup and view all the answers

<p>During atrial contraction, the AV valves remain open, allowing blood to flow from the atria to the ventricles while the semilunar valves stay closed.</p> Signup and view all the answers

<p>End-systolic volume (ESV) is the volume of blood remaining in the ventricle after contraction, typically around 60 mL.</p> Signup and view all the answers

<p>Backflow into the atria is prevented as atrial contraction compresses the openings for major veins, maintaining one-way blood flow.</p> Signup and view all the answers

<p>During isovolumic relaxation, the ventricles relax with no change in blood volume while the semilunar valves close and AV valves remain shut.</p> Signup and view all the answers

<p>Atrial systole involves the contraction of the atria, which pushes blood into the ventricles through the open AV valves, enhancing ventricular filling.</p> Signup and view all the answers

<p>The plateau prolongs the refractory period, preventing tetany by allowing the muscle to contract and relax fully before being stimulated again.</p> Signup and view all the answers

<p>Skeletal muscle fibers have a short refractory period of about 1 to 2 milliseconds, allowing for high-frequency stimulation and the potential for sustained contraction (tetany).</p> Signup and view all the answers

<p>The P wave represents the electrical changes associated with atrial depolarization, occurring before the contraction of the atria.</p> Signup and view all the answers

<p>The QRS complex reflects the electrical changes associated with ventricular depolarization, leading to the contraction of the ventricles.</p> Signup and view all the answers

<p>A lengthened P-R interval may indicate first-degree AV block, which can signal problems in the heart's conduction system.</p> Signup and view all the answers

<p>Ventricular fibrillation is marked by chaotic electrical activity in the ventricles, leading to uncoordinated muscle contractions and stopping blood circulation.</p> Signup and view all the answers

<p>An AED analyzes the heart's rhythm and can deliver a shock to restore a normal rhythm during conditions like ventricular fibrillation.</p> Signup and view all the answers

<p>Second-degree AV block may result in some atrial action potentials failing to reach the ventricles, possibly causing irregular heartbeats.</p> Signup and view all the answers

<p>The Q-T interval measures the time from ventricular depolarization to repolarization, and an elongated Q-T interval may lead to serious arrhythmias.</p> Signup and view all the answers

<p>A flattened T wave may indicate potential issues with ventricular repolarization or decreased cardiac health.</p> Signup and view all the answers

<p>Ventricular ejection occurs during the systolic phase, where blood is pumped out of the ventricles into the arteries.</p> Signup and view all the answers

<p>The T wave represents ventricular repolarization, crucial for allowing the ventricles to prepare for the next contraction.</p> Signup and view all the answers

<p>The long refractory period due to the plateau in cardiac muscle cells prevents tetany, allowing full contraction and relaxation.</p> Signup and view all the answers

<p>The five phases are atrial relaxation and ventricular filling, atrial contraction and ventricular filling, isovolumic contraction, ventricular ejection, and isovolumic relaxation.</p> Signup and view all the answers

<p>The semilunar valves prevent backflow of blood from the arterial trunks into the ventricles.</p> Signup and view all the answers

<p>Blood flow direction is determined by the relative pressure of the ventricles compared to their associated arterial trunks.</p> Signup and view all the answers

<p>All heart valves are closed simultaneously during this phase.</p> Signup and view all the answers

<p>Cardiac output is the amount of blood pumped by the heart per minute and is calculated as CO = SV x HR.</p> Signup and view all the answers

<p>The left ventricle must be larger and stronger to pump blood through the systemic circulation.</p> Signup and view all the answers

<p>Stroke volume is the amount of blood ejected from the ventricles during systole and is calculated as SV = EDV - ESV.</p> Signup and view all the answers

<p>The dicrotic notch represents a temporary drop in pressure in the aorta when the aortic semilunar valve closes.</p> Signup and view all the answers

<p>Cardiac reserve is the increase in cardiac output above resting levels and indicates an individual's capacity for physical effort.</p> Signup and view all the answers

<p>Maintaining normal resting cardiac output ensures that all body tissues receive adequate perfusion.</p> Signup and view all the answers

<p>Individuals with smaller hearts often have a smaller stroke volume, necessitating a higher heart rate to maintain normal cardiac output.</p> Signup and view all the answers

<p>A cardiac cycle is the set of changes in the heart from the start of one heartbeat to the start of the next.</p> Signup and view all the answers

<p>The P wave represents atrial depolarization, the QRS complex represents ventricular depolarization, and the T wave represents ventricular repolarization.</p> Signup and view all the answers

<p>The closing of the AV valves is caused by the pressure difference between the atria and ventricles.</p> Signup and view all the answers

<p>During intense exercise, cardiac output increases significantly to meet the body's heightened oxygen and nutrient demands.</p> Signup and view all the answers

<p>Sympathetic stimulation increases the firing rate of the SA node by releasing norepinephrine (NE) and epinephrine (EPI), which enhance Ca2+ influx into these cells.</p> Signup and view all the answers

<p>Preload is the stretch of the heart muscle before contraction and is crucial for determining stroke volume; an increase in preload leads to a larger stroke volume.</p> Signup and view all the answers

<p>Caffeine is a positive chronotropic agent that increases heart rate, while the parasympathetic nervous system is a negative chronotropic agent that decreases heart rate.</p> Signup and view all the answers

<p>An increase in afterload decreases stroke volume because the heart must work harder to eject blood, leading to reduced efficiency.</p> Signup and view all the answers

<p>Thyroid hormone increases the number of β-adrenergic receptors on SA nodal cells, making them more responsive to norepinephrine and epinephrine.</p> Signup and view all the answers

<p>Inotropic agents alter the force of contraction of the myocardium; positive inotropic agents increase it, while negative inotropic agents decrease it.</p> Signup and view all the answers

<p>An increase in venous return raises preload, resulting in an increased stroke volume, while a decrease in venous return lowers stroke volume.</p> Signup and view all the answers

<p>Sympathetic stimulation decreases the delay in the AV node and increases the conduction rate, thus enhancing heart rate.</p> Signup and view all the answers

<p>The Frank-Starling law states that an increase in end-diastolic volume (preload) leads to an increase in stroke volume due to greater stretch of cardiac muscle.</p> Signup and view all the answers

<p>Nicotine acts as a positive chronotropic agent, increasing heart rate by stimulating the sympathetic nervous system.</p> Signup and view all the answers

<p>Cardiac output is determined by both heart rate and stroke volume.</p> Signup and view all the answers

<p>Afterload is the resistance faced during ejection, influenced by the diameter of the arteries and blood viscosity.</p> Signup and view all the answers

<p>Cocaine acts as a positive chronotropic agent, thereby increasing heart rate through sympathetic stimulation.</p> Signup and view all the answers

<p>Venous return increases due to more time for blood to fill the heart.</p> Signup and view all the answers

<p>Atherosclerosis increases afterload, which decreases stroke volume and cardiac output.</p> Signup and view all the answers

<p>Norepinephrine and epinephrine increase the heart's contractility and therefore raise cardiac output.</p> Signup and view all the answers

<p>Electrolyte imbalances can act as negative inotropic agents, reducing cardiac output.</p> Signup and view all the answers

<p>Increased venous return raises stroke volume due to enhanced preload.</p> Signup and view all the answers

<p>A patent foramen ovale.</p> Signup and view all the answers

<p>Chest pain and radiation of pain to the arm and jaw.</p> Signup and view all the answers

<p>Cardiac output can approximately double due to increased venous return and heart rate.</p> Signup and view all the answers

<p>Chronotropic agents influence heart rate by acting on the SA and AV nodes.</p> Signup and view all the answers

<p>It increases the heart rate by reducing parasympathetic input.</p> Signup and view all the answers

<p>The net effect on cardiac output cannot be predicted without knowing the relative changes.</p> Signup and view all the answers

<p>They attach the AV valves to the ventricular walls and prevent prolapse during contraction.</p> Signup and view all the answers

<p>The left anterior descending artery and the circumflex artery.</p> Signup and view all the answers

<p>The heart starts developing in the third week, with the primitive heart tube forming by day 21.</p> Signup and view all the answers

<p>Bradycardia is a resting heart rate below 60 beats per minute, caused by conditions like hypothyroidism.</p> Signup and view all the answers

<p>Atria have lower pressure and do not need to pump blood as far as ventricles.</p> Signup and view all the answers

<p>Increased Ca2+ enhances contractility, leading to higher stroke volume and cardiac output.</p> Signup and view all the answers

<p>Calcium channel blockers.</p> Signup and view all the answers

<p>It may lead to cyanosis or other symptoms.</p> Signup and view all the answers

<p>Venous return, inotropic agents, and afterload all impact stroke volume.</p> Signup and view all the answers

<p>Positive inotropic agents increase ejection fraction by enhancing heart contractility.</p> Signup and view all the answers

<p>Afterload is inversely correlated with cardiac output; increased afterload can decrease it.</p> Signup and view all the answers

<p>The single heart tube partitions into four chambers and forms the great vessels.</p> Signup and view all the answers

<p>It increases both heart rate and the force of contraction.</p> Signup and view all the answers

<p>SA node, AV node, AV bundle, bundle branches, Purkinje fibers.</p> Signup and view all the answers

<p>They allow Na+ and Ca2+ to enter, helping to reach the depolarization threshold.</p> Signup and view all the answers

<p>It prevents tetanus and ensures that the heart chambers have enough time to relax and fill with blood.</p> Signup and view all the answers

<p>Increased venous return enhances stroke volume by providing more blood to fill the heart.</p> Signup and view all the answers

<p>It leads to an increase in heart rate through positive chronotropic effects.</p> Signup and view all the answers

<p>It separates the pulmonary circulation from systemic circulation, allowing normal blood flow patterns.</p> Signup and view all the answers

<ol> <li>Atrial relaxation and ventricular filling, 2. Atrial contraction and ventricular filling, 3. Isovolumic contraction, 4. Ventricular ejection, 5. Isovolumic relaxation.</li> </ol> Signup and view all the answers

<p>The influx of Na+ and Ca2+ through open voltage-gated cation and calcium channels triggers depolarization.</p> Signup and view all the answers

<p>Positive inotropic agents increase stroke volume, while negative inotropic agents decrease it.</p> Signup and view all the answers

<p>The filling rate of the atria decreases, providing the heart time to properly fill.</p> Signup and view all the answers

<p>Cardiac output is calculated as the heart rate multiplied by stroke volume.</p> Signup and view all the answers

<p>It generates electrical impulses spontaneously, setting the rhythm for heart contractions.</p> Signup and view all the answers

<p>Atrial contraction pushes additional blood into the ventricles, increasing their preload.</p> Signup and view all the answers

<p>The ventricles contract with no change in volume, building pressure before ejecting blood.</p> Signup and view all the answers

<p>Bradycardia is a condition characterized by a persistently low resting heart rate. Potential causes include hypothyroidism and electrolyte imbalances.</p> Signup and view all the answers

<p>The heart begins as a single primitive heart tube that bends and folds, eventually becoming partitioned into four chambers. This process occurs in the third week of embryonic development.</p> Signup and view all the answers

<p>The atrioventricular valves are located between the atria and ventricles of the heart. They regulate blood flow during contraction and relaxation cycles.</p> Signup and view all the answers

<p>Coronary arteries supply blood to the heart wall. They branch off from the ascending aorta and ensure that the heart muscle receives the oxygen and nutrients it needs.</p> Signup and view all the answers

<p>If the foramen ovale does not close, blood would flow from the right atrium to the left atrium, potentially causing enlargement of the right side of the heart. This condition can lead to various complications.</p> Signup and view all the answers

<p>Intercalated discs comprise desmosomes and gap junctions, linking cardiac muscle cells together. They facilitate the passage of action potentials and ensure synchronized contractions.</p> Signup and view all the answers

<p>Incomplete septal development can lead to conditions such as atrial septal defect, where there remains an opening between the left and right atria. This can affect heart function and lead to complications.</p> Signup and view all the answers

<p>The sinoatrial (SA) node initiates the action potential that stimulates heart contractions. It acts as the natural pacemaker of the heart, dictating the rhythm.</p> Signup and view all the answers

<p>The fibrous skeleton provides attachment sites for heart valves and cardiac muscle, while also preventing action potentials from spreading between the atria and ventricles except through the AV node. This ensures coordinated contraction.</p> Signup and view all the answers

<p>The pericardial cavity, containing serous fluid, reduces friction between the heart's surfaces during contractions. This lubrication is essential for smooth heart movement.</p> Signup and view all the answers