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Cardiac Muscle Excitability and Action Potential

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Cardiac Muscle Excitability and Action Potential

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Questions and Answers

During which phase of the cardiac action potential does the resting membrane potential across the myocardial cell membrane reach about -90 mV?

Phase 0 (Depolarization) (correct)

Phase 2 (Plateau)

Phase 3 (Complete repolarization)

Phase 1 (Early repolarization)

What causes the rapid upstroke of the action potential during Phase 0 of the cardiac action potential?

Release of Ca2+ from the sarcoplasmic reticulum

Inward Ca2+ current through L-type Ca channels

Rapid Na+ influx by voltage gated Na+ channels (correct)

Outward K+ current resulting in repolarization

Which phase of the cardiac action potential is characterized by inward Ca2+ current balanced by outward K+ current, resulting in little change in membrane potential?

Phase 2 (Plateau) (correct)

Phase 0 (Depolarization)

Phase 3 (Complete repolarization)

Phase 1 (Early repolarization)

What triggers muscle contraction in cardiac muscle during the plateau phase of the action potential?

Release of Ca2+ from the sarcoplasmic reticulum (D) Signup and view all the answers

What occurs during Phase 3 (Complete repolarization) of the cardiac action potential?

L-type Ca channels close, but K+ currents still exist (A) Signup and view all the answers

What prevents tetany in cardiac muscle during the action potential?

Long duration of the action potential (D) Signup and view all the answers

During which phase does the cardiac muscle not respond to any stimulus?

Phase 2 (A) Signup and view all the answers

What is the nature of the heart's ability to beat at regular intervals?

Myogenic (B) Signup and view all the answers

Which node has the highest rhythmicity of discharge of cardiac impulses?

Sino-atrial node (SAN) (C) Signup and view all the answers

What happens to heart rate as a result of sympathetic supply?

Increases (A) Signup and view all the answers

What is the function of the enzymes Na+/K+-ATPase & Na+/Ca2+ exchange during Phase 4?

Removal of excess Na+ & Ca2+ from the cell (A) Signup and view all the answers

Which factor decreases heart rate as a negative chronotropic factor?

Alkalosis (B) Signup and view all the answers

What is essential for the heart's rhythmicity due to its mainly aerobic metabolism?

$O_2$ supply (C) Signup and view all the answers

Which phase corresponds to late phase 3 and allows the heart cell to begin responding to excitation again?

Phase 3 (B) Signup and view all the answers

Innervation of the heart by sympathetic supply increases rhythmicity of the whole heart including which part?

Ventricles (D) Signup and view all the answers