Cardiac Muscle Structure and Function
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Questions and Answers

What role do the valves in veins play?

  • They prevent blood from flowing towards the heart.
  • They allow blood to flow in both directions.
  • They increase blood pressure in the veins.
  • They regulate the return of blood to the heart. (correct)

    • What effect does standing motionless have on foot vein pressure?

  • It maintains a stable pressure in the foot veins.
  • It decreases foot vein pressure significantly.
  • It causes pressure to escalate to +90 mmHg. (correct)
  • It prevents blood from entering the foot veins.

    • What is the primary cause of varicose veins?

  • Nerve damage in the limbs.
  • Increased blood pressure in the veins. (correct)
  • Inflammation of the surface skin.
  • Weakening of capillaries.

    • Which system is primarily responsible for short-term blood pressure regulation?

    <p>Neural mechanisms. (B)</p> Signup and view all the answers

    Which statement accurately describes the venous pump?

    <p>It is caused by the tightening of leg muscles. (C)</p> Signup and view all the answers

    What happens to diastolic duration when heart rate increases?

    <p>Diastolic duration shortens. (D)</p> Signup and view all the answers

    How is cardiac output calculated?

    <p>CO = Stroke Volume × Heart Rate (D)</p> Signup and view all the answers

    What causes the S1 heart sound?

    <p>Closure of the atrioventricular valves. (C)</p> Signup and view all the answers

    Which artery supplies the left atrium?

    <p>Circumflex Artery (B)</p> Signup and view all the answers

    What is the primary ion involved in the resting phase of cardiomyocyte action potential?

    <p>Potassium (K+) (C)</p> Signup and view all the answers

    What occurs at the beginning of ventricular diastole?

    <p>Closure of semilunar valves (aortic and pulmonary). (D)</p> Signup and view all the answers

    What effect does an increased heart rate have on stroke volume?

    <p>Stroke volume decreases. (C)</p> Signup and view all the answers

    Which part of the coronary circulation supplies the right ventricle?

    <p>Right Coronary Artery (RCA) (A)</p> Signup and view all the answers

    What is the primary function of the myocardium layer in the heart wall?

    <p>To contract and pump blood (D)</p> Signup and view all the answers

    Which structure is responsible for the rapid transmission of electrical signals across cardiomyocytes?

    <p>Intercalated discs (A)</p> Signup and view all the answers

    What separates the atrial syncytium from the ventricular syncytium?

    <p>Annulus fibrosus (B)</p> Signup and view all the answers

    What occurs during isovolumic relaxation?

    <p>Valves are closed and no blood flows. (B)</p> Signup and view all the answers

    What change happens during ventricular ejection?

    <p>Atrioventricular valves are closed. (A)</p> Signup and view all the answers

    Where is the SA (sinoatrial) node primarily located?

    <p>Near the entrance of the superior vena cava (A)</p> Signup and view all the answers

    What type of muscle tissue is present in the myocardium?

    <p>Striated muscle with involuntary function (B)</p> Signup and view all the answers

    What is the normal resting adult heart rate range?

    <p>60-100 bpm (C)</p> Signup and view all the answers

    What is the firing frequency of the AV (atrioventricular) node?

    <p>40-60 beats per minute (C)</p> Signup and view all the answers

    During which phase do the AV valves close?

    <p>Isovolumic contraction (B)</p> Signup and view all the answers

    What is the definition of bradycardia?

    <p>A heart rate below 60 bpm at rest. (B)</p> Signup and view all the answers

    What is the sequence of conduction through the heart starting from the SA node?

    <p>SA node, AV node, His bundle, Purkinje fibers (B)</p> Signup and view all the answers

    What type of heart rhythm is produced by the impulses from the SA node?

    <p>Sinus rhythm (B)</p> Signup and view all the answers

    What happens to the durations of systole and diastole when heart rate increases?

    <p>Both systolic and diastolic durations shorten. (D)</p> Signup and view all the answers

    What defines tachycardia?

    <p>A heart rate above 100 bpm. (C)</p> Signup and view all the answers

    During atrial contraction, what is the primary function?

    <p>Blood is forced under pressure into the ventricles. (D)</p> Signup and view all the answers

    What characterizes phase 0 of the cardiac action potential?

    <p>Influx of sodium (Na+) (A)</p> Signup and view all the answers

    What primarily prevents additional impulses from spreading during phase 2 of the action potential?

    <p>Calcium (Ca2+) influx (D)</p> Signup and view all the answers

    Which phase of the cardiac action potential involves the reopening of potassium (K+) channels?

    <p>Phase 3 (A)</p> Signup and view all the answers

    What is the resting membrane potential of the SA node cells?

    <p>-60 mV (D)</p> Signup and view all the answers

    What function do funny channels serve in the SA node?

    <p>Bring resting membrane potential closer to threshold (A)</p> Signup and view all the answers

    Which factor contributes to the SA node's ability to spontaneously generate action potentials?

    <p>Presence of funny Na+ leak channels (A)</p> Signup and view all the answers

    What is the primary role of veins in the circulatory system?

    <p>Store and transport blood back to the heart (B)</p> Signup and view all the answers

    Why is the SA node referred to as the primary pacemaker of the heart?

    <p>It can generate action potentials autonomously (C)</p> Signup and view all the answers

    What is the primary role of the DIAD in cardiac muscle contraction?

    <p>Transmitting the action potential from the T tubule to the sarcoplasmic reticulum and triggering calcium release. (A)</p> Signup and view all the answers

    How does the DIAD structure differ from that of skeletal muscle?

    <p>DIAD is a simpler structure than a triad, consisting of one T tubule and one terminal cisternae. (C)</p> Signup and view all the answers

    Which of the following statements accurately describes the contraction dynamics of cardiac muscle compared to skeletal muscle?

    <p>Cardiac muscle contractions are slower and less regular than skeletal muscle contractions. (B)</p> Signup and view all the answers

    Which pair of valves are found on the left side of the heart?

    <p>Bicuspid valve, Aortic valve (B)</p> Signup and view all the answers

    Which of the following is NOT a branch of the aorta?

    <p>Left common iliac artery (B)</p> Signup and view all the answers

    What is the main reason for the interventricular septum being thicker than the interatrial septum?

    <p>To generate more pressure during ventricular contraction. (B)</p> Signup and view all the answers

    Which of the following statements regarding heart valves is TRUE?

    <p>Heart valves are passive structures that open and close based on pressure gradients. (A)</p> Signup and view all the answers

    What is the anatomical positioning of the human heart within the chest cavity?

    <p>In the left mediastinum, at the level of thoracic vertebrae T5-T8 (C)</p> Signup and view all the answers

    Study Notes

    Cardiac Muscle

    • Located in the middle layer of the heart (myocardium)
    • Situated between the endocardium (inner layer) and epicardium (outer layer)
    • Composed of cardiomyocytes
    • Cardiomyocytes are short, branched, and interconnected
    • Connected by intercalated discs for electrical and mechanical communication

    Cardiac Muscle Layers

    • Epicardium: The outermost layer of the heart
      • Protects the heart from external impacts
      • Coronary arteries and nerves pass through this layer
      • Composed of thin connective tissue and mesothelium
    • Myocardium: The middle and thickest layer
      • Composed of cardiomyocytes
      • Responsible for pumping blood
      • Striated muscle cells connected by intercalated discs
    • Endocardium: The innermost layer
      • Lines the heart chambers and valves
      • Provides a smooth surface to direct blood flow
      • Composed of thin connective tissue and endothelial cells

    Cardiac Muscle Tissue Structures

    • Intercalated Discs: Connections between cardiomyocytes
      • Gap junctions: Facilitate rapid electrical impulse transmission
      • Desmosomes: Provide mechanical strength, maintaining cell connection during contractions
      • Striations: Similar to skeletal muscle, due to the organized arrangement of actin and myosin filaments

    Cardiac Muscle Tissue DIAD

    • DIAD is a structure unique to cardiac muscle cells, formed by the t-tubule and terminal cisternae of the sarcoplasmic reticulum.
    • Unlike skeletal muscle, cardiac muscle has DIADS (dyadic structure), not TRIADS, facilitating calcium regulation.
    • Tubular structures (t-tubules) extending deep within the cell, derived from the sarcolemma
    • Terminal cisternae: Calcium-storing part of the sarcoplasmic reticulum

    Cardiac Muscle Contraction

    • Contraction begins with calcium ions entering the cell (calcium-induced calcium release)
    • DIAD transmits action potential from the t-tubule to the sarcoplasmic reticulum
    • calcium release from the terminal cisternae initiates contraction
    • Contraction mechanism differs slightly compared to skeletal muscle due to different structural arrangement (DIAD/TRIAD difference)

    Cardiac Anatomy

    • The heart is located in the middle mediastinum, at the level of thoracic vertebrae 5-8
    • Four chambers: two atria (atria are positioned above the ventricles), two ventricles
    • Internal septa separate the right and left sides of the heart
      • Interventricular septum: Thicker than the interatrial septum due to greater ventricular pressure needed during contraction
    • Blood enters the right atrium from the superior and inferior vena cava
    • The aorta branches into the brachiocephalic artery, left carotid artery, and left subclavian artery

    Heart Valves

    • One-way valves in the heart ensuring unidirectional blood flow
      • Atrioventricular (AV) valves (tricuspid and bicuspid valves) regulate blood flow between atria and ventricles
      • Semilunar valves (pulmonary and aortic valves) control blood flow out of the ventricles
    • The opening and closing of the valves passively depends on the pressure gradient.

    Heart Wall

    • Consists of three layers
      • Endocardium (innermost)
      • Myocardium (middle)
      • Epicardium (outermost)
    • Cardiomyocytes are responsible for the contraction function
    • Intercalated discs (bridges) facilitate rapid signal transmission throughout the heart

    Heart Syncytia

    • The heart has two distinct functional syncytia: atrial and ventricular
    • Separated by fibrous tissue (annulus fibrosus)
    • Atria contract first because their syncytia is separate from the ventricles

    Heart Rate

    • The frequency of heart contractions per minute (bpm)
    • Normal resting adult human heart rate is 60-100 bpm
    • Heart rate varies according to physical needs

    Heart Rate Regulation

    • Tachycardia: heart rate > 100 bpm
    • Bradycardia: heart rate < 60 bpm
    • Arrhythmia: Irregular heart rhythm

    Cardiac Output

    • The volume of blood pumped by the heart per minute (ml/min)
      • Cardiac output (CO) = Stroke volume (SV) x Heart rate (HR)
    • Normal cardiac output value for a typical adult is about 5600 ml/min (70ml/beat x 80 beats/min)

    Factors Affecting Heart Rate and Stroke Volume

    • Autonomic nervous system (sympathetic and parasympathetic)
    • Hormones (e.g., epinephrine, norepinephrine, thyroxine, adrenaline)
    • Exercise
    • Blood volume, pressure
    • Stress

    Blood Pressure Regulation

    • Blood Pressure is regulated in two ways
      • Short-term: Neural (vasomotor center in medulla oblongata, Baroreceptors), rapid changes
      • Long-term: Hormonal (renin-angiotensin-aldosterone, ADH), slower response
    • Blood Volume fluctuations affect blood pressure
      • High volume leads to increased blood pressure
      • Low volume leads to decreased blood pressure

    Coronary Circulation

    • Coronary arteries supply the myocardium with oxygen and nutrients.
    • Two main arteries come from the ascending aorta:
      • Left coronary artery (LCA) that branches into left anterior descending (LAD) and circumflex arteries
      • Right coronary artery (RCA) supplying the right side of the heart.

    Venous Circulation

    • Blood from all systemic veins is collected into the right atrium via the superior and inferior vena cava
    • Veins are capacitance vessels, capable of storing blood
    • Valves prevent backflow.

    Heart Sounds

    • S1: "Lub" sound (beginning of ventricular systole), closure of the AV valves
    • S2: "Dub" sound (beginning of ventricular diastole), closure of the semilunar valves
    • Crucial for assessing cardiac function

    Cardiac Action Potential (ventricle)

    • Resembles normal action potentials, but with specific phases
    • Phase 0: Depolarization
    • Phase 1: Early Repolarization
    • Phase 2: Plateau phase (important, delayed repolarization)
    • Phase 3: Repolarization
    • Phase 4: Resting phase
    • Channels involved in these phases: Na+, Ca2+, and K+.

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    Cardiac Muscle Physiology PDF

    Description

    Explore the fascinating anatomy and physiology of cardiac muscle. This quiz covers the three layers of the heart, their function, and the unique structure of cardiomyocytes. Test your knowledge on how electrical and mechanical communication occurs in cardiac tissue.

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