Unlike smooth and skeletal muscle, cardiac muscle tissue is capable of
The Correct Answer is {"dropdown-group-1":"D"}
A. Distension: Cardiac muscle tissue is capable of stretching to accommodate varying volumes of blood, a property shared with smooth muscle (in blood vessels and hollow organs) and skeletal muscle to some extent. Distension alone does not distinguish cardiac muscle from other muscle types.
B. Relaxation: Relaxation is a fundamental property of all muscle types, including skeletal, smooth, and cardiac muscle. After contraction, all these muscles return to their resting length to allow subsequent filling or preparation for the next contraction.
C. Contracting: Contraction is a universal property of all muscle types. Skeletal, smooth, and cardiac muscles all contract via actin–myosin cross-bridge cycling in response to appropriate stimuli.
D. Autorhythmicity: Cardiac muscle is unique in its ability to generate spontaneous action potentials without external nervous stimulation. Specialized pacemaker cells within the sinoatrial node initiate rhythmic depolarization, allowing the heart to maintain a coordinated and continuous heartbeat. This intrinsic automaticity is distinct from skeletal and smooth muscle, which require neural or hormonal stimuli to contract.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is D
Explanation
A. P wave:: The P wave represents atrial depolarization, indicating electrical activation of the atria. It precedes atrial contraction and is the first deflection on a standard ECG tracing. Normal duration is ≤0.12 seconds.
C. T wave: The T wave reflects ventricular repolarization, showing the recovery phase of the ventricles after contraction. Its shape and amplitude can indicate electrolyte imbalances, ischemia, or other cardiac abnormalities.
F. QT segment: The QT segment (more accurately called the QT interval), labelled as F, represents the total time for ventricular depolarization and repolarization. It begins at the start of the QRS complex and ends at the conclusion of the T wave on an electrocardiogram (ECG). It reflects the entire period of ventricular electrical activity, including contraction and recovery.
D. PR interval: The PR interval represents the time for electrical conduction from the atria through the AV node to the ventricles. Normal duration is 0.12–0.20 seconds, with prolongation suggesting conduction delay.
Correct Answer is B
Explanation
Correct answer: False
Preload refers to the degree of stretch of the ventricular myocardial fibers at the end of diastole, just before ventricular contraction. It is influenced by the volume of blood returning to the heart (venous return) and the compliance of the ventricular walls. End-diastolic volume (EDV) is the actual volume of blood present in the ventricle at the end of diastole. While preload is closely related to EDV, it is a functional measure of myocardial fiber stretch rather than a direct measurement of blood volume. Thus, preload describes the mechanical tension on the myocardium, whereas EDV quantifies the volume of blood in the chamber.
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