Cardiac Action Potentials - Video Tutorials & Practice Problems
Introduction to Action Potential in Cardiac Cells
Cardiac Action Potentials Example 1
Which of the following correctly identifies a difference between action potentials in cardiac and skeletal muscle?
Skeletal muscles utilize K+ and Ca+2 during action potentials while cardiac contractile cells use K+ and Na+.
Action potentials in cardiac contractile and cardiac pacemaker cells are longer lasting than action potentials in skeletal muscle.
Cardiac pacemaker cells have a slow repolarization while skeletal muscles have a slow depolarization.
The action potentials in each type of tissue are the same.
Pacemakers: Molecular Physiology
Cardiac Action Potentials Example 2
Calcium ion channels open in response to changes in membrane potential. What type of opening mechanism do calcium ion channels in cardiac muscle exhibit?
Ligand-gated.
Voltage-gated.
Mechanically-gated.
Time-gated.
Autorhythmicity is a unique feature of cardiac pacemaker cells. What feature of cardiac pacemaker cells allows them to be autorhythmic while other cardiac cells are not?
Pacemaker cells use Ca+2 ions, unlike other action potentials.
Sodium channels in pacemaker cells allow both calcium and sodium to pass through.
The pacemaker potential is stimulated by polarization of the cell.
Unlike other action potentials, the first channel to open is the potassium channel, leading to repolarization.
Contractile Tissue: Molecular Physiology
Cardiac Action Potentials Example 3
Cardiac contractile tissue uses sodium, calcium, and potassium channels for depolarization and repolarization. During which phase of the action potential is the calcium channel open?
Depolarization phase.
Plateau phase.
Repolarization phase.
Resting phase.
How would you expect the absolute refractory period of a contractile cell to change if more potassium channels opened sooner after polarization?
Absolute refractory period would increase.
Absolute refractory period would decrease.
There would be no change; absolute refractory period is determined by the calcium ion channels.
It’s impossible to tell as opening potassium channels will have an unpredictable effect on sodium channels.
Comparing Action Potentials in Pacemaker and Contractile Cells
Cardiac Action Potentials Example 4
The movement of ions in opposite directions at the same time is responsible for which of the following?
Slow depolarization in cardiac pacemaker cells.
Slow repolarization in cardiac pacemaker cells.
Slow depolarization in cardiac contractile cells.
Both A & C are correct.
Which statement below correctly describes how the channels that are active during the pacemaker potential are different from other ion channels used in action potentials?
They are voltage gated.
They are active over a much wider range of voltages than other ion channels.
They allow Ca+2 ions to pass out of the cell.
They allow both Na+ and K+ through the same channel.
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