Cardiac Action Potential: Multiple Choice Questions

Group 1

• Phase 0 - Rapid depolarization
• Phase 1 - Initial repolarization
• Phase 2 - Plateau
• Phase 3 - Rapid repolarization
• Phase 4 - Resting potential
• Phase 5 - Hyperpolarization

• Sodium (Na+)
• Potassium (K+)
• Calcium (Ca2+)
• Chloride (Cl-)
• Magnesium (Mg2+)

• Rapid influx of Na+ ions
• Efflux of K+ ions
• Influx of Ca2+ ions
• Efflux of Cl- ions
• Influx of Mg2+ ions

• Phase 0
• Phase 1
• Phase 2
• Phase 3
• Phase 4

• Efflux of K+ ions
• Influx of Na+ ions
• Influx of Ca2+ ions
• Efflux of Cl- ions
• Influx of Mg2+ ions

• It is longer than the action potential in skeletal muscle.
• It involves a plateau phase.
• It does not involve calcium ions.
• It is shorter than the action potential in neurons.
• It is initiated by the opening of potassium channels.

• Contributes to the plateau phase
• Triggers muscle contraction
• Causes rapid depolarization
• Causes rapid repolarization
• Is not involved in the cardiac action potential

• Voltage-gated sodium channels
• Voltage-gated potassium channels
• Voltage-gated calcium channels
• Ligand-gated chloride channels
• Voltage-gated magnesium channels

• Maintained by the Na+/K+ pump
• Negative inside relative to outside
• Positive inside relative to outside
• Maintained by the Ca2+ pump
• No ion movement occurs

• Prevents tetanus in cardiac muscle
• Allows time for the heart to refill with blood
• Allows for rapid successive action potentials
• Increases the strength of contraction
• Decreases the strength of contraction

• Heart rate
• Ion channel mutations
• Temperature
• Blood pressure
• Oxygen levels

• It helps maintain the resting membrane potential.
• It pumps 3 Na+ out and 2 K+ in.
• It pumps 2 Na+ out and 3 K+ in.
• It is active during the action potential.
• It does not require ATP.

• Closure of Na+ channels
• Opening of K+ channels
• Opening of Ca2+ channels
• Closure of K+ channels
• Opening of Na+ channels

• Phase 2
• Phase 0
• Phase 1
• Phase 3
• Phase 4

• It is due to the influx of Ca2+ ions.
• It prolongs the action potential.
• It is due to the efflux of Na+ ions.
• It shortens the action potential.
• It occurs during Phase 3.

• Responsible for repolarization
• Contributes to resting membrane potential
• Causes depolarization
• Responsible for the plateau phase
• Not involved in the action potential

• It prevents the heart from undergoing tetanus.
• It ensures unidirectional propagation of the action potential.
• It allows for immediate re-excitation of the heart muscle.
• It shortens the duration of the action potential.
• It is not present in cardiac cells.

• Influx of Ca2+ ions
• Efflux of K+ ions
• Influx of Na+ ions
• Efflux of Na+ ions
• Influx of Cl- ions

• Decrease the duration of the plateau phase
• Reduce the force of cardiac contraction
• Increase the rate of depolarization
• Increase the duration of the plateau phase
• Increase the force of cardiac contraction

• Na+ influx causes rapid depolarization
• K+ efflux causes repolarization
• Ca2+ influx contributes to the plateau phase
• Cl- influx causes depolarization
• Mg2+ influx contributes to the plateau phase

• Increases intracellular calcium
• Increases the force of contraction
• Decreases the duration of the action potential
• Decreases intracellular sodium
• Decreases the force of contraction

• Responsible for the rapid depolarization phase
• Contributes to the plateau phase
• Responsible for repolarization
• Not involved in the action potential
• Contributes to the resting membrane potential

• Decreases the resting membrane potential
• Increases the excitability of cardiac cells
• Increases the resting membrane potential
• Decreases the excitability of cardiac cells
• Has no effect on cardiac action potentials

• Prolongs the duration of the action potential
• Decreases the force of contraction
• Shortens the duration of the action potential
• Increases the force of contraction
• Has no effect on cardiac action potentials

• Sympathetic stimulation increases heart rate
• Parasympathetic stimulation decreases heart rate
• Sympathetic stimulation decreases heart rate
• Parasympathetic stimulation increases heart rate
• The autonomic nervous system has no effect on heart rate