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These flashcards cover key concepts related to cardiac electrophysiology, the ECG, and excitation-contraction coupling in heart muscle.
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What is the inherent rate of the SA node in the absence of neural or hormonal input?
Approximately 100 depolarizations per minute.
What happens if the AV node malfunctions due to drugs or disease?
It may reduce or completely eliminate the transmission of action potentials from the atria to the ventricles.
What is the ventricular rate when the bundle of His becomes the pacemaker?
Generally 25 to 40 beats/min, out of sync with atrial contractions.
What is the current treatment for severe AV conduction disorders?
Permanent surgical implantation of an artificial pacemaker.
What does the QRS complex represent in an ECG?
Ventricular depolarization.
What does the T wave represent in an ECG?
Ventricular repolarization.
Why Atrial repolarization is usually not evident on the ECG?
Because it occurs at the same time as the QRS complex.
What is a pacemaker potential?
A slow depolarization in SA node cells that brings the membrane potential to threshold.
What causes the depolarizing phase of an action potential in nodal cells?
Calcium influx through L-type calcium channels.
What does the pacemaker potential provide the SA node with?
Automaticity, the capacity for spontaneous, rhythmical self-excitation.
What does the ECG measure?
Currents generated in the extracellular fluid by changes occurring simultaneously in many cardiac cells.
What triggers contraction of heart muscle?
An increase in the cell's cytosolic calcium concentration.
What is the role of T-tubules in cardiac muscle?
To spread the plasma membrane action potential into the interior of muscle cells.
What channels open in the T-tubule during excitation-contraction coupling in cardiac muscle?
Voltage-sensitive calcium channels (L-type).
What is calcium-induced calcium release?
The release of a large amount of calcium from the sarcoplasmic reticulum into the cytosol, triggered by an initial small increase in cytosolic calcium.
How cytosolic calcium concentration is restored to its original extremely low value?
By active transport of calcium back into the sarcoplasmic reticulum.
What is the result of the long absolute refractory period of cardiac muscle?
The muscle cannot be re-excited in time to produce summation.
What is systole?
The period of ventricular contraction and blood ejection.
What is diastole?
A period of ventricular relaxation and blood filling.