Cardiac Muscle Contraction
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Questions and Answers

What is the primary function of contractile cells in the heart?

  • To produce powerful contractions that propel blood (correct)
  • To control and coordinate the activities of other cells
  • To regulate the permeability of ions
  • To generate action potentials spontaneously

    • What is the result of sympathetic stimulation on the heart?

  • Increased heart rate due to increased permeability to sodium and calcium (correct)
  • Increased permeability to potassium
  • Hyperpolarization of the SA node
  • Decreased heart rate

    • What is the role of autorhythmic cells in the heart?

  • To generate action potentials spontaneously
  • To control and coordinate the activities of contractile cells (correct)
  • To regulate the permeability of ions
  • To produce powerful contractions that propel blood

    • What ion is involved in the depolarization of the SA node?

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

    What is the effect of parasympathetic stimulation on the heart?

    <p>Decreased heart rate</p> Signup and view all the answers

    What is the function of funny channels in the heart?

    <p>More permeable to sodium than potassium</p> Signup and view all the answers

    What determines the force of contraction in cardiac muscle?

    <p>Calcium levels</p> Signup and view all the answers

    What is the effect of digitalis on the heart rate?

    <p>Slows heart rate down</p> Signup and view all the answers

    In which direction does the depolarization wave spread in the ventricles?

    <p>From bottom to top</p> Signup and view all the answers

    What is the name of the wave that represents the depolarization of the atria?

    <p>P-wave</p> Signup and view all the answers

    What is the term for a heart rate that is faster than normal?

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

    What is the term for a restricted blood flow to the heart?

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

    What is the effect of G-protein on calcium channels?

    <p>Opens calcium channels</p> Signup and view all the answers

    What is the term for an abrupt reduction in coronary blood flow to a segment of myocardium?

    <p>Myocardial infarction</p> Signup and view all the answers

    Study Notes

    Heart Function and Electrical Conduction

    • Heart relaxation occurs when ventricles fill with blood.
    • Contraction of the heart occurs from the apex to the base.

    Cardiac Muscle Cells

    • Contractile cells make up the bulk of atrial and ventricular walls and produce powerful contractions to propel blood.
    • Ca2+ binding to troponin triggers muscle contraction.
    • Autorhythmic cells (pacemakers) control and coordinate contractile cells.

    Action Potentials

    • The first action potential occurs in the SA node, resulting in depolarization.
    • The second action potential occurs in the myocardium, resulting in contraction.
    • Cardiac muscle cells can generate action potentials spontaneously without nervous stimulation.

    Ion Channels and Stimulation

    • Funny channels (If) are more permeable to sodium than potassium, allowing depolarization.
    • Sympathetic stimulation alters permeability to different ions, exciting beta 1 receptors and increasing heart rate.
    • Catecholamines (e.g., adrenaline) stimulate the heart.
    • Parasympathetic stimulation increases pacemaker potential, hyperpolarizing SA node cells and slowing the heart rate.

    Depolarization and Repolarization

    • Depolarization of the SA node involves calcium.
    • Sodium is involved in myocardium depolarization.
    • The cardiac action potential has three stages: rapid depolarization, plateau, and repolarization.

    Calcium-Induced Calcium Release and Muscle Contraction

    • Calcium-induced calcium release triggers muscle contraction.
    • Cardiac muscle contraction can be graded, with calcium levels determining the force of contraction.
    • G-proteins open calcium channels, increasing calcium release and muscle contraction.

    Drugs and the Heart

    • Digitalis blocks the sodium-potassium channel, increasing intracellular sodium and calcium, and slowing the heart rate.

    Electrical Conduction in the Heart

    • The SA node, internodal pathways, AV node, AV bundle, bundle branches, and Purkinje fibers coordinate contraction in the heart.
    • The atria contract while the ventricles relax, and vice versa.

    Electrocardiogram (EKG)

    • An EKG represents the summed electrical activity of all cells recorded from the surface of the body.
    • Waves, segments, and intervals are used to analyze the EKG.
    • The axis of the EKG represents the general movement of the waveform.

    EKG Components

    • The P wave represents atrial depolarization and systole.
    • The PR interval is the time from the onset of the P wave to the beginning of the QRS complex.
    • The QRS complex represents ventricular depolarization.
    • The ST segment represents the time at which the entire ventricle is depolarized.
    • The Q-T interval represents ventricular repolarization.

    Abnormal Heart Rhythms

    • Tachycardia: a heart rate faster than normal.
    • Bradycardia: a heart rate slower than normal.
    • Arrhythmia: an irregular heartbeat.

    Heart Pathologies

    • Ischemia: insufficient blood flow to the heart.
    • Hypoxia: low levels of oxygen.
    • Anoxia: absence of oxygen.
    • Myocardial infarction: abrupt reduction in coronary blood flow to a segment of myocardium.
    • Stenosis: restricted blood flow.

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    Description

    This quiz covers the mechanisms of cardiac muscle contraction, including the role of autorhythmic and contractile cells, action potentials, and calcium ions.

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