Which structural feature is found in skeletal muscle fibers but not in cardiac contractile cells?
Myoglobin and lipid inclusions
A single nucleus per cell
Triads formed by long T tubules and cisternae of the sarcoplasmic reticulum
Sarcomeres along myofibrils
The Correct Answer is C
A. Myoglobin and lipid inclusions: Both skeletal and cardiac muscle fibers contain myoglobin, which stores oxygen for aerobic metabolism, and lipid inclusions as energy reserves. These features support high metabolic demands in both muscle types and are not unique to skeletal muscle.
B. A single nucleus per cell: Cardiac muscle cells are typically uninucleated, whereas skeletal muscle fibers are multinucleated. However, the presence of a single nucleus is characteristic of cardiac myocytes, not a distinguishing feature of skeletal muscle.
C. Triads formed by long T tubules and cisternae of the sarcoplasmic reticulum: Skeletal muscle fibers have well-organized triads, where a T tubule is flanked by two terminal cisternae of the sarcoplasmic reticulum, allowing rapid calcium release for synchronous contraction. In contrast, cardiac contractile cells have diads (one T tubule with one adjacent cisterna) and smaller T tubules, reflecting slower calcium handling.
D. Sarcomeres along myofibrils: Both skeletal and cardiac muscle fibers contain sarcomeres arranged along myofibrils, giving them striated appearance under microscopy. Sarcomeres are essential for contraction in both types of striated muscle and are not a distinguishing structural feature.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
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.
Correct Answer is D
Explanation
A. It is caused only by infections: Heart failure has multiple causes, including chronic hypertension, coronary artery disease, myocardial infarction, valvular disorders, and cardiomyopathies. While infections such as myocarditis can contribute, they are not the sole cause.
B. It always results in a heart attack: Heart failure is a condition of impaired cardiac function, whereas a heart attack (myocardial infarction) is an acute event caused by coronary artery blockage. Heart failure may develop after a heart attack, but it does not always result from one.
C. It does not affect blood circulation: Heart failure directly impairs the heart’s ability to pump blood effectively, reducing cardiac output and often causing fluid buildup in the lungs and systemic circulation. Circulatory compromise is a hallmark of the condition.
D. It is a condition where the heart can't pump blood properly: Heart failure occurs when the myocardium cannot generate sufficient force to maintain adequate blood flow to meet the body’s metabolic demands. This can involve systolic dysfunction (impaired contraction), diastolic dysfunction (impaired filling), or a combination, leading to fluid retention, congestion, and reduced tissue perfusion.
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