Myocardial conducting cells have
The Correct Answer is {"dropdown-group-1":"B"}
A. the same number of: Myocardial conducting cells do not have the same density of myofibrils as contractile cells. While they contain some contractile proteins, their primary function is impulse conduction rather than force generation, so their myofibril content is significantly lower.
B. fewer: Myocardial conducting cells, including those in the sinoatrial node, atrioventricular node, and Bundle of His, have fewer myofibrils compared to contractile cardiomyocytes. This structural adaptation allows them to focus on rapid generation and conduction of electrical impulses rather than strong contraction.
C. no: Conducting cells are not completely devoid of myofibrils. They retain some actin and myosin filaments, enabling minor contractile activity, but this is minimal compared to contractile myocardial cells.
D. more: Conducting cells do not require additional myofibrils, as their primary role is impulse initiation and propagation, not forceful contraction. Excess filaments would impede their conduction efficiency and slow electrical signal transmission.
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Correct Answer is B
Explanation
Correct answer: False
The atrioventricular (AV) node, located in the lower portion of the interatrial septum near the tricuspid valve, functions as a critical electrical relay between the atria and ventricles. While the SA node sets the normal heart rhythm, the AV node limits the number of impulses transmitted to the ventricles, providing a protective delay that allows adequate ventricular filling. Under extreme SA node stimulation, impulses exceeding 220 per minute can overwhelm the AV node, resulting in ineffective ventricular contractions, reduced cardiac output, and compromised heart function. The AV node’s intrinsic conduction limits are essential for maintaining coordinated and efficient cardiac performance.
Correct Answer is C
Explanation
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.
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