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What initiates the rapid depolarization phase in contractile myocytes?
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The rapid depolarization phase is initiated by a Na+ influx when a neighboring cell triggers the contraction.
How do 'funny' currents contribute to pacemaker activity?
'Funny' currents involve a Na+ influx beginning below -40mV, which leads to gradual depolarization and initiates an action potential in pacemaker cells.
What occurs during the refractory period in cardiac muscle cells?
The long absolute refractory period prevents tetanus and ensures the heart muscle relaxes before a new contraction is initiated.
How do action potentials differ between pacemaker cells and contractile myocytes?
Pacemaker cells have no true resting potential and initiate spontaneous action potentials with 'funny' Na+ currents, whereas contractile myocytes have a stable resting potential and are triggered by Na+ influx from neighboring cells.
How does the calcium/sodium exchange contribute after heart contraction?
Calcium is transported out of the cell and back into the sarcoplasmic reticulum to restore ionic conditions post-contraction.
What is the role of cardiac myocytes in heart function?
Cardiac myocytes are specialized muscle cells responsible for the contraction of the heart to pump blood.
What would happen if the SA node were damaged?
Other parts of the conduction system, like the AV node, can take over pacing the heart, albeit possibly at a slower rate.
What is the resting potential of contractile myocytes, and how is it maintained?
Contractile myocytes have a stable resting potential of -90mV, maintained by the sodium/potassium pump.
How is blood expulsion from heart chambers ensured by cardiac action potentials?
The prolonged plateau phase allows for a sustained contraction, which is essential for efficient blood expulsion from the heart chambers.
What is the function of the SA node in cardiac physiology?
The SA node acts as the primary pacemaker of the heart, initiating action potentials that establish the heart rate.
Explain the role of calcium in cardiac muscle contraction.
Calcium influx triggers calcium-induced calcium release from the sarcoplasmic reticulum, which initiates contraction through the sliding filament mechanism.
How do gap junctions facilitate cardiac function?
Gap junctions enable ionic flow and electrical coupling between cardiac cells, allowing the rapid spread of action potentials.
Describe the significance of the plateau phase in cardiac action potentials.
The plateau phase prolongs contraction due to balanced Ca++ influx and K+ efflux, crucial for effective blood expulsion from the heart.
What is the function of the AV node during cardiac conduction?
The AV node slows the conduction of impulses to allow time for atrial contraction before the ventricles contract.
Why is the prevention of tetanus important in the heart?
Preventing tetanus ensures that the heart can relax completely between beats, allowing for consistent pumping and preventing overlap that would impair function.
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