The Correct Answer is {"dropdown-group-1":"B"}
A. Fibers: Muscle fibers refer to the individual elongated cells of cardiac or skeletal muscle, containing myofibrils responsible for contraction. While fibers make up the structural unit of the myocardium, they do not provide specialized junctions for direct ionic communication between cells and therefore do not synchronize cardiac contraction.
B. Gap junctions: Gap junctions are specialized intercellular connections located within intercalated discs of cardiac muscle. They consist of connexin proteins that form channels allowing ions, such as sodium and calcium, to flow directly between adjacent cardiomyocytes. This electrical coupling enables rapid propagation of action potentials and synchronized contraction of the myocardium during each heartbeat.
C. Desmosomes: Desmosomes are structural protein complexes within intercalated discs that mechanically anchor cardiac muscle cells to one another. They prevent cells from separating during the high mechanical stress of contraction but do not facilitate ionic flow or electrical coupling between cells.
D. Sarcolemma: The sarcolemma is the plasma membrane of a muscle cell, including cardiac myocytes, which encases the cytoplasm and myofibrils. It propagates action potentials along individual cells but does not form intercellular channels for direct ion passage between adjacent cardiac cells.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
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Correct Answer is {"dropdown-group-1":"B"}
Explanation
A. Aortic: The aortic valve is a semilunar valve located between the left ventricle and the aorta. It opens during ventricular systole to allow blood ejection into the systemic circulation and closes during diastole to prevent backflow. Its closure produces the S2 heart sound, not S1.
B. Atrioventricular: The atrioventricular (AV) valves, comprising the tricuspid and mitral (bicuspid) valves, are located between the atria and ventricles. During ventricular contraction (systole), these valves close to prevent backflow into the atria. The closure of the AV valves generates the first heart sound (S1), commonly described as "lub," marking the onset of systole.
C. Semilunar: The semilunar valves, including the aortic and pulmonary valves, prevent backflow from the arteries into the ventricles. Their closure occurs at the end of ventricular systole and produces the second heart sound (S2), which is distinct from the "lub" of S1.
D. Pulmonary: The pulmonary valve is another semilunar valve located between the right ventricle and the pulmonary artery. It opens during right ventricular systole and closes during diastole. Its closure contributes to the S2 heart sound rather than S1.
Correct Answer is {"dropdown-group-1":"B"}
Explanation
A. P: The P wave represents atrial depolarization. It reflects the electrical activity as the impulse spreads from the sinoatrial (SA) node across the atrial myocardium, causing atrial contraction. Because the atria are smaller than the ventricles, the electrical signal is smaller in amplitude.
B. QRS: The QRS complex represents ventricular depolarization. It corresponds to the rapid spread of electrical impulses through the ventricles via the bundle branches and Purkinje fibers, leading to ventricular contraction. Since the ventricles have significantly greater muscle mass than the atria, this depolarization produces a larger and stronger electrical signal on the ECG.
C. T: The T wave represents ventricular repolarization, the process by which ventricular muscle cells return to their resting membrane potential after contraction. It does not represent depolarization.
D. PR: The PR interval reflects the time required for the electrical impulse to travel from the atria through the atrioventricular (AV) node to the ventricles. It represents conduction delay, not ventricular depolarization itself.
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