15 Questions
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)
What causes the rapid upstroke of the action potential during Phase 0 of the cardiac action potential?
Rapid Na+ influx by voltage gated Na+ channels
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)
What triggers muscle contraction in cardiac muscle during the plateau phase of the action potential?
Release of Ca2+ from the sarcoplasmic reticulum
What occurs during Phase 3 (Complete repolarization) of the cardiac action potential?
L-type Ca channels close, but K+ currents still exist
What prevents tetany in cardiac muscle during the action potential?
Long duration of the action potential
During which phase does the cardiac muscle not respond to any stimulus?
Phase 2
What is the nature of the heart's ability to beat at regular intervals?
Myogenic
Which node has the highest rhythmicity of discharge of cardiac impulses?
Sino-atrial node (SAN)
What happens to heart rate as a result of sympathetic supply?
Increases
What is the function of the enzymes Na+/K+-ATPase & Na+/Ca2+ exchange during Phase 4?
Removal of excess Na+ & Ca2+ from the cell
Which factor decreases heart rate as a negative chronotropic factor?
Alkalosis
What is essential for the heart's rhythmicity due to its mainly aerobic metabolism?
$O_2$ supply
Which phase corresponds to late phase 3 and allows the heart cell to begin responding to excitation again?
Phase 3
Innervation of the heart by sympathetic supply increases rhythmicity of the whole heart including which part?
Ventricles
This quiz covers the definition of excitability in cardiac muscle and the phases of fast response action potential. It includes topics such as depolarization and the changes in membrane potential during excitation.
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