What happens during repolarization of cardiac conducting cells?
The sodium ion channels open, allowing Na+ to enter the cell.
The calcium ion channels open, allowing Ca2+ to enter the cell.
Sodium ion channels close, preventing Na+ from entering.
Potassium ion channels open, allowing K+ to leave the cell.
The Correct Answer is D
A. The sodium ion channels open, allowing Na+ to enter the cell: Opening of sodium channels occurs during the depolarization phase of cardiac action potentials, not repolarization. The influx of Na+ rapidly raises the membrane potential, initiating the action potential and triggering subsequent calcium influx for contraction.
B. The calcium ion channels open, allowing Ca2+ to enter the cell: Calcium channels open primarily during the plateau phase (phase 2) of the cardiac action potential, allowing Ca2+ entry to sustain contraction. This occurs before repolarization and contributes to excitation-contraction coupling rather than the return to resting membrane potential.
C. Sodium ion channels close, preventing Na+ from entering: Sodium channel closure occurs immediately after depolarization and contributes to the refractory period, but it does not itself drive repolarization. The cell requires potassium efflux to restore the resting membrane potential.
D. Potassium ion channels open, allowing K+ to leave the cell: During repolarization (phase 3) of cardiac conducting cells, voltage-gated potassium channels open, permitting K+ to exit the cytoplasm. The outward movement of positively charged K+ restores the negative resting membrane potential, terminating the action potential and preparing the cell for the next depolarization.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
Correct answer: True
Purkinje fibers are specialized conduction fibers located in the subendocardial layer of the ventricles, extending from the bundle branches to distribute impulses throughout the ventricular myocardium. Under normal conditions, they rapidly conduct impulses initiated by the SA node via the AV node to coordinate ventricular contraction. If the AV node is blocked, the Purkinje fibers can act as a backup pacemaker, generating spontaneous impulses at an intrinsic rate of approximately 30–40 beats per minute. This slower rate maintains minimal ventricular contraction, but it is insufficient to sustain adequate cardiac output for normal physiologic demands over extended periods.
Correct Answer is {"dropdown-group-1":"C","dropdown-group-2":"B"}
Explanation
Correct answer:
- Interventricular septum
- Atrioventricular (AV) bundle / Bundle of His
The highlighted area represents the interventricular septum, the thick muscular wall that separates the right and left ventricles. It forms the medial wall of both ventricles and extends from the atrioventricular valves superiorly to the apex inferiorly. Its primary physiologic function is to prevent mixing of oxygenated blood in the left ventricle with deoxygenated blood in the right ventricle while also contributing to ventricular contraction. The electrical conduction structure that passes through this area is the atrioventricular (AV) bundle / Bundle of His. The Bundle of His passes from the atrioventricular node into the membranous portion of the interventricular septum. It then divides into the right and left bundle branches, which travel along the septum toward the apex to distribute electrical impulses to both ventricles. This allows coordinated ventricular depolarization and synchronized contraction.
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