A person takes a drug that blocks slows gap junction activity. Which effect is most likely? reduced SA node rhythm reduced rate of conduction in subendocardial fibers reduced AV node conduction speed reduced rate of depolarization of ventricular cardiomyocytes
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Gap junctions are essential for the propagation of electrical signals between cells in the heart, allowing for coordinated contraction and rhythm. Show more…
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E) heart block. 2. In the condition known as complete heart block, what happens? A) Coronary arteries are blocked by plaques, preventing blood and oxygen from reaching the myocardial contractile cells. B) Electrical signals from the SA node never reach the ventricles, so the contraction of the atria is not coordinated with the contraction of the ventricles. C) The fibrous skeleton of the heart breaks down, interfering with the passage of blood from the atria to the ventricles. D) The mitral valve leaflets calcify and close, preventing blood from being pumped efficiently by the left side of the heart. E) Blood flow through the foramen ovale is blocked. 3. ECGs A) provide direct information about the heart function. B) are most useful in diagnosing heart murmurs. C) show the "summed" electrical potentials generated by all cells of the heart. D) have two major components: waves and nodes. E) measure the mechanical activity of the heart. 4. The P wave of an ECG corresponds to A) the depolarization of the atria. B) the progressive wave of ventricular depolarization. C) the repolarization of the ventricles. D) atrial repolarization. E) None of the answers are correct. 5. The QRS complex of an ECG corresponds to A) the depolarization of the atria. B) ventricular depolarization and atrial repolarization C) the repolarization of the ventricles. D) atrial repolarization. E) None of the answers are correct. 6. Ventricular contraction A) begins during the first part of the P wave. B) begins just after the T wave. C) begins just after the Q wave. D) begins during the latter part of the P wave. E) None of the answers are correct. 7. Atrial contraction A) begins during the first part of the P wave. B) begins just after the T wave. C) begins just after the Q wave. D) begins during the latter part of the P wave. E) None of the answers are correct.
Adi S.
1. If you blocked extracellular Ca++ channels in myocardial contractile cells, what would happen to the refractory period? - it would be shorter - it would remain the same - it would be longer 2. The depolarization of the action potential of non-pacemaker cardiac contractile cells is due to the ________. - inward diffusion of K+ - inward diffusion of Ca2+ - inward diffusion of Na+ - outward diffusion of K+ 3. What is a main difference between the extracellular Ca++ channels in autorhythmic cells and those in myocardial contractile cells? - the direction they let Ca++ move in - what part of an action potential they are involved in - the neurotransmitter they bind 4. What causes the semilunar valves to close? - Higher pressure in the atria than in the ventricles - Higher pressure in the aorta and pulmonary trunk than in the ventricles - Higher pressure in the ventricles than in the atria - Higher pressure in the ventricles than in the aorta and pulmonary trunk 7. The plateau of the action potential in cardiac contractile ventricular cells results from the opening of voltage-gated __________ channels in the plasma membrane of the cell. - Ca2+ - Cl- - K+ - Na+ 8. Which of the following statements about membrane potentials in different types of cardiac cells is TRUE? - Once threshold depolarization is reached in both myocardial and pacemaker cells, the rapid upswing of the action potential is caused by the opening of voltage-gated Na+ channels - Myocardial contractile cells have a resting membrane potential of about -90 mV; pacemaker cells do not have a true resting membrane potential. - Voltage-gated Ca2+ channels cause a plateau which extends the repolarization phase for both autorhythmic and contractile cells - The SA node has a long plateau phase to ensure it beats at the right rhythm. 9. Threshold is usually stimulated in contractile cardiac muscles by - ACh attaching to receptors - Ca++ influx from outside the cell - Ca++ and other cation leakage through gap junctions - K+ influx from the extracellular fluid 10. A drug blocks If channels, what would the outcome be? The parasympathetic and sympathetic system are working as they normally are when the body is at rest. - no effect - slowed heart rate - increased heart rate 11. The depolarization of the action potential of cardiac pacemaker cells is caused by________. - inward diffusion of Na+ - inward diffusion of Ca2+ - inward diffusion of K+ - outward diffusion of K+
Ahmad is a 66-year-old male patient who has mild to moderate heart failure. This patient takes a drug that causes partial inhibition of Na Ca exchanger at the membrane of cardiomyocytes. This drug will increase all of the following except: a. The refractory period b. Cardiac cycle length c. Number of heart beats per minute d. The duration of plateau phase of action potential
Crystal W.
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