18 Questions
During which phase of the cardiac action potential do the Na+ channels close, preventing further action potential production?
Phase 0: rapid depolarization
Which phase of the cardiac action potential is referred to as the 'absolute refractory period'?
Phase 2: plateau phase
What is a characteristic of the 'relative refractory period' in the cardiac action potential?
Action potential generation is inhibited
Which phase of the cardiac action potential marks the transition from depolarization to repolarization?
Phase 1: early repolarization
What happens to the Na+ channels during the plateau phase of the cardiac action potential?
They remain closed
In which phase of the cardiac action potential does repolarization occur?
Phase 3: rapid repolarization
What characterizes phase 0 of the cardiac action potential?
Opening of sodium gates leading to rapid depolarization
Which phase of the cardiac action potential is characterized by a hundred-fold increase in sodium permeability?
Phase 0: Rapid depolarization
What is the defining feature of phase 1 in the cardiac action potential?
Rapid, partial early repolarization
During which phase of the cardiac action potential does the plateau phase occur?
Phase 2: Plateau phase
Which phase marks the complete repolarization in the cardiac action potential?
Phase 2: Plateau phase
At what membrane potential does the resting phase (phase 4) occur in cardiac myocytes?
-85 mV
During which phase of the cardiac action potential does Na+ influx take place down its electrochemical gradient?
Phase 0: rapid depolarization
Which phase is characterized by the membrane potential rising to between +20 and +30 mV?
Phase 0: rapid depolarization
What causes the membrane potential to fall to a value close to the potassium equilibrium potential in phase 3?
Increased K+ channel opening
Which event causes the release of a larger quantity of Ca++ from the sarcoplasmic reticulum in the cardiac action potential cycle?
Simultaneous opening of L-type voltage gated calcium channels
Which phase is characterized by K+ permeability beginning to increase and K+ leaving the cell at an increased rate?
Phase 1: early repolarization
At which stage of the cardiac action potential cycle does the membrane potential begin again from the resting potential?
Phase 4: resting phase
Learn about the significance of the long plateau phase in the cardiac action potential and its impact on the heart's functioning. Understand how individual contractions in the heart muscle cannot fuse into a maintained tetanic contraction due to this unique characteristic.
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