Cardiac Muscle Cell Channels
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Questions and Answers

What type of channels participate in depolarization at the membrane of cardiac muscle cells?

  • Fast voltage-gated K+ channels
  • Slow voltage-gated Ca2+ channels
  • Voltage-gated Na+ channels (correct)
  • Non-voltage gated Cl- channels

    • Which ion is significant in the normal function of cardiac muscle cells?

  • Potassium (K+)
  • Chloride (Cl-)
  • Calcium (Ca2+) (correct)
  • Sodium (Na+)

    • What happens to the membrane potential during depolarization of cardiac muscle cells?

  • It changes from -90 mV to +30 mV
  • It remains at +30 mV
  • It remains at -90 mV
  • It changes from +30 mV to -90 mV (correct)

    • What triggers the opening of fast voltage-gated Na+ channels in the sarcolemma of cardiac muscle cells?

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

    In which direction does Ca2+ move in response to the opening of voltage-gated Ca2+ channels in cardiac muscle cells?

    <p>Into the cell</p> Signup and view all the answers

    Which ion channel is involved in the repolarization of the membrane of cardiac muscle cells?

    <p>Voltage-gated K+ channels</p> Signup and view all the answers

    What is the main difference between the refractory period of skeletal and cardiac muscle cells?

    <p>Skeletal muscle has a shorter refractory period.</p> Signup and view all the answers

    What condition is characterized by sustained muscle contraction without any relaxation?

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

    Why can skeletal muscle be restimulated at a frequency that does not allow for complete relaxation?

    <p>Due to its short refractory period.</p> Signup and view all the answers

    In skeletal muscle fibers, what occurs while sarcomeres are still contracting?

    <p>Repolarization at the sarcolemma.</p> Signup and view all the answers

    What event delays repolarization in cardiac muscle cells, leading to a longer refractory period?

    <p>Plateau event at the sarcolemma.</p> Signup and view all the answers

    How long does it take for muscle contraction and relaxation associated with sarcomeres in cardiac muscle cells to occur?

    <p>Approximately 250 milliseconds.</p> Signup and view all the answers

    What are the three variables that may influence stroke volume?

    <p>Venous return, presence of inotropic agents, and afterload</p> Signup and view all the answers

    What is the typical end-diastolic volume (EDV) in a resting adult?

    <p>130 mL</p> Signup and view all the answers

    What is the typical end-systolic volume (ESV) in a resting adult?

    <p>60 mL</p> Signup and view all the answers

    How is stroke volume (SV) calculated?

    <p>SV = EDV - ESV</p> Signup and view all the answers

    What is the primary mechanism by which sympathetic stimulation increases heart rate?

    <p>Sympathetic stimulation increases Ca2+ influx into SA nodal cells, causing them to reach threshold more quickly</p> Signup and view all the answers

    Which of the following factors can influence end-diastolic volume (EDV)?

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

    Which of the following factors can influence end-systolic volume (ESV)?

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

    Which of the following is NOT a positive chronotropic agent mentioned in the text?

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

    How does thyroid hormone increase heart rate?

    <p>Thyroid hormone increases the number of $\beta_1$-adrenergic receptors on SA nodal cells</p> Signup and view all the answers

    What is the role of protein kinase enzymes in the sympathetic regulation of heart rate?

    <p>Protein kinase enzymes phosphorylate Ca2+ channels, causing them to open and increasing Ca2+ influx into SA nodal cells</p> Signup and view all the answers

    Which of the following is a direct effect of sympathetic stimulation on the AV node?

    <p>Sympathetic stimulation increases Ca2+ influx into AV nodal cells, decreasing the delay and increasing the conduction rate</p> Signup and view all the answers

    Which of the following is a mechanism by which chemical compounds can increase heart rate?

    <p>Chemical compounds increase Ca2+ influx into SA nodal cells, causing them to reach threshold more quickly</p> Signup and view all the answers

    What causes the atrioventricular (AV) valves to close and the semilunar valves to open during ventricular ejection?

    <p>Increased pressure in the ventricles and decreased pressure in the aorta and pulmonary artery</p> Signup and view all the answers

    What is the end-diastolic volume?

    <p>The total amount of blood in the ventricles at the end of ventricular relaxation</p> Signup and view all the answers

    What is the relationship between end-diastolic volume, end-systolic volume, and stroke volume?

    <p>Stroke volume = end-diastolic volume - end-systolic volume</p> Signup and view all the answers

    What is the primary function of the cardiac output?

    <p>To transport respiratory gases, nutrients, and other substances throughout the body</p> Signup and view all the answers

    Which phase of the cardiac cycle is associated with ventricular contraction?

    <p>Ventricular systole</p> Signup and view all the answers

    Which of the following statements about the cardiac cycle is true?

    <p>The AV valves close during ventricular relaxation</p> Signup and view all the answers

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