Cardiac Muscle Anatomy and Function
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Questions and Answers

Which layer of the heart is primarily responsible for the heart's pumping action?

  • Pericardium
  • Epicardium
  • Endocardium
  • Myocardium (correct)

    • What is the unique cellular structure that facilitates electrical communication and mechanical connection between cardiomyocytes?

  • Intercalated discs (correct)
  • Sarcomeres
  • T tubules
  • Desmosomes

    • Which component of the intercalated discs provides mechanical strength and helps cells stay together during contraction?

  • Desmosomes (correct)
  • T tubules
  • Myofilaments
  • Gap junctions

    • What is the primary role of the endocardium?

    <p>To line the heart chambers and valves, ensuring smooth blood flow</p> Signup and view all the answers

    What does the 'DIAD' structure in cardiac muscle cells consist of?

    <p>One T tubule and one terminal cisterna</p> Signup and view all the answers

    What is the outermost layer of the heart called?

    <p>Epicardium</p> Signup and view all the answers

    What creates the striated appearance of cardiac muscle cells?

    <p>The arrangement of actin and myosin filaments</p> Signup and view all the answers

    What is the function of the T-tubules in the DIAD structure of cardiac muscle cells?

    <p>To transmit electrical impulses</p> Signup and view all the answers

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

    <p>It functions as the heart muscle responsible for contractions.</p> Signup and view all the answers

    Which structure separates the atrial syncytium from the ventricular syncytium?

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

    What is the role of pacemaker cells in the heart?

    <p>They generate spontaneous electrical impulses.</p> Signup and view all the answers

    Which node serves as the primary pacemaker of the heart?

    <p>SA node</p> Signup and view all the answers

    What is the conduction speed of the AV node?

    <p>0.05 m/s</p> Signup and view all the answers

    What is the term for the rapid spread of a signal across cardiomyocytes in the heart?

    <p>Syncytium</p> Signup and view all the answers

    What is the primary function of the valves in the veins?

    <p>To prevent blood from returning away from the heart</p> Signup and view all the answers

    How many impulses per minute does the SA node typically produce?

    <p>60-80 impulses</p> Signup and view all the answers

    What is the function of the His bundle in the heart's electrical conduction system?

    <p>To transmit signals from the atria to the ventricles</p> Signup and view all the answers

    What happens to blood pressure in the foot veins when a person stands motionless for 30 seconds?

    <p>It increases to +90 mmHg</p> Signup and view all the answers

    Which system is primarily responsible for long-term regulation of blood pressure?

    <p>Renin-angiotensin-aldosterone system</p> Signup and view all the answers

    What is one consequence of increased pressure in the capillaries due to standing for long periods?

    <p>Fluid leaking into the interstitial space causing leg swelling</p> Signup and view all the answers

    What is the result of weakened or damaged vein valves?

    <p>Blood accumulation in the veins</p> Signup and view all the answers

    What role does DIAD play in cardiac muscle contraction?

    <p>It transmits the action potential from the T tubule to the sarcoplasmic reticulum.</p> Signup and view all the answers

    How does the contraction mechanism of cardiac muscle differ from that of skeletal muscle?

    <p>Cardiac muscle has a less regular and slower contraction dynamics.</p> Signup and view all the answers

    Where is the human heart located within the body?

    <p>In the middle mediastinum at thoracic vertebrae T5-T8.</p> Signup and view all the answers

    Which statement accurately describes the structure of the heart valves?

    <p>Atrioventricular valves are found between atria and ventricles.</p> Signup and view all the answers

    What is the primary function of the heart's septa?

    <p>To separate the left and right sides of the heart.</p> Signup and view all the answers

    Which artery branches directly from the aorta in the proper sequence?

    <p>Brachiocephalic artery, left carotid artery, left subclavian artery.</p> Signup and view all the answers

    What determines the opening and closing of the heart valves?

    <p>Pressure gradients in the heart chambers.</p> Signup and view all the answers

    What is the composition of the interventricular septum compared to the interatrial septum?

    <p>Thicker due to higher pressure generation requirements.</p> Signup and view all the answers

    During which stage are the semilunar valves closed?

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

    What occurs during the ventricular filling phase?

    <p>Atrial contraction forces blood into the ventricles</p> Signup and view all the answers

    Which condition indicates a heart rate above 100 bpm at rest?

    <p>Tachycardia</p> Signup and view all the answers

    What happens to the heart rate during sleep?

    <p>Decreases to around 40-50 bpm</p> Signup and view all the answers

    Which value indicates bradycardia?

    <p>Below 60 bpm</p> Signup and view all the answers

    During which stage is blood flow in the ventricles stopped?

    <p>Isovolumic relaxation</p> Signup and view all the answers

    What characterizes an arrhythmia?

    <p>Irregular beating pattern</p> Signup and view all the answers

    What is the heart rate range for a normal resting adult human?

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

    What happens during Phase 0 of the action potential?

    <p>Sodium channels open, allowing Na+ to flow into the cell.</p> Signup and view all the answers

    What is the primary role of the plateau phase (Phase 2) in cardiac muscle?

    <p>To allow time for the heart muscle to pump blood effectively.</p> Signup and view all the answers

    What distinguishes the resting membrane potential of SA node cells from that of normal cardiomyocyte cells?

    <p>SA node cells have a resting potential closer to the action potential threshold.</p> Signup and view all the answers

    During Phase 3 (repolarization), what occurs in the cell?

    <p>Potassium channels open and calcium channels close.</p> Signup and view all the answers

    What initiates the spontaneous activity of SA node cells?

    <p>The presence of funny leak Na+ channels.</p> Signup and view all the answers

    Why are veins referred to as capacitance vessels?

    <p>They can store blood due to their ability to contract and relax.</p> Signup and view all the answers

    What occurs during Phase 1 (early repolarization)?

    <p>Potassium channels open, leading to potassium efflux.</p> Signup and view all the answers

    What is the typical resting membrane potential of a normal cardiomyocyte cell?

    <p>-90 mV</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 the epicardium (outer layer)
    • Cells are called cardiomyocytes
    • Cardiomyocytes are short, branched, and interconnected
    • Connected by intercalated discs, facilitating electrical and mechanical communication

    Cardiac Muscle Cell Structure

    • Cardiomyocytes are short, branched, and interconnected
    • Interconnected via intercalated discs (providing electrical and mechanical connections)

    Cardiac Muscle Layers

    • Epicardium: The outermost layer of the heart; protective; contains coronary arteries and nerves
    • Structure: Thin connective tissue and mesothelium
    • Myocardium: The middle, thickest layer; responsible for pumping blood; composed of cardiomyocytes
    • Structure: Striated muscle cells connected by intercalated discs
    • Endocardium: The innermost layer; smooth lining of heart chambers and valves; directs blood flow; composed of thin connective tissue and endothelial cells

    Cardiac Muscle Layers - Further Detail

    • Myocardium: The thickest and most important layer, responsible for heart pumping
    • Functions: Cardiac muscle layer that pumps blood
    • Cardiomyocytes: Perform the contraction function; striated muscle cells connected by intercalary discs
    • Structure: Striated muscle cells (cardiomyocytes) connected by intercalated discs

    Cardiac Muscle Cells: DIAD

    • The structure found in cardiac muscle cells
    • Integrates electrical and mechanical events in the muscle cell

    Cardiac Action Potential Phases

    • Phase 0 (Depolarization): Rapid Na+ influx
    • Phase 1 (Early Repolarization): Brief K+ efflux
    • Phase 2 (Plateau): Persistent Ca2+ influx; balanced by delayed outward K+ efflux
    • Phase 3 (Repolarization): K+ efflux
    • Phase 4 (Resting Potential): Only K+ channels open, membrane potential approximately -90mV

    SA Node Pacemaker Potential

    • Specialized cardiomyocytes
    • Resting potential is closer to 0 than in normal cardiomyocytes (-60mV to -55mV)
    • Threshold value for depolarization is lower than normal pacemaker cells
    • Allows for automatic rhythmic depolarization

    Funny Channels

    • Na+ leak channels
    • Cause resting membrane potential to be less negative
    • Allows SA node cells to spontaneously generate depolarization
    • Facilitates rhythmic activity without nerve stimulation

    Venous Circulation

    • Veins act as capacitance vessels, storing blood
    • Blood from systemic veins collects in the right atrium
    • Veins have low contractility
    • Veins have valves to direct blood toward the heart
    • Foot vein pressure increases during standing (90 mmHg)

    Heart Rate

    • Frequency of heart contractions per minute (bpm)
    • Varies based on physical needs
    • Normal resting adult HR: 60-100 bpm

    Cardiac Output

    • Volume of blood pumped by the heart per minute
    • Calculated as: Cardiac Output = Stroke Volume x Heart Rate
    • Normal CO in adults: ~5600 mL/min

    Heart Sounds

    • S1 (Lub): Closure of AV valves (tricuspid and mitral); beginning of ventricular systole
    • S2 (Dub): Closure of semilunar valves (aortic and pulmonary); end of ventricular systole

    Coronary Circulation

    • Branches of arteries supply myocardium with oxygen and nutrients
    • Left Coronary Artery (LCA):
      • Left anterior descending (LAD) artery, supplies front and large part of the septum
      • Circumflex artery, wraps around left side of heart
    • Right Coronary Artery (RCA): Branches from aorta, supplies right atrium, right ventricle and part of septum

    Blood Pressure Regulation

    • Short-term: Neural mechanisms (baroreceptors) adjust blood vessel diameter
    • Long-term: Hormonal mechanisms (renin-angiotensin-aldosterone system) regulate blood volume and sodium reabsorption.

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    Description

    Test your knowledge on the anatomy and function of cardiac muscle. This quiz covers various components of the heart, including layers, cellular structures, and unique features of cardiomyocytes. Challenge yourself to understand the vital roles these structures play in maintaining heart function.

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