In an isotonic contraction, the muscle:
rapidly resynthesizes creatine phosphate and ATP
maintains the same length while generating tension
changes length while maintaining constant tension
remains relaxed and passive during movement
The Correct Answer is C
Choice A reason: This choice confuses metabolic processes with mechanical muscle activity. While creatine phosphate and ATP are essential for muscle contraction, their resynthesis is not specific to isotonic contraction. These energy molecules are replenished during recovery phases and are not the defining feature of isotonic contractions.
Choice B reason: This describes isometric contraction, not isotonic. In isometric contractions, the muscle generates force without changing its length—such as holding a plank position. Isotonic contractions, by contrast, involve a change in muscle length.
Choice C reason: This is the correct answer. Isotonic contractions involve the muscle changing length while maintaining constant tension. There are two types: concentric (muscle shortens) and eccentric (muscle lengthens). These contractions are typical in dynamic movements like lifting or lowering weights.
Choice D reason: This is incorrect. Muscles do not remain relaxed during isotonic contractions. Instead, they actively contract and generate force to produce movement. Passive relaxation does not contribute to the mechanics of isotonic contraction.
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Related Questions
Correct Answer is D
Explanation
Choice A reason: Cross bridges are formed between actin and myosin during contraction. T tubules do not hold them in place; their role is electrical, not structural.
Choice B reason: While T tubules are embedded in the muscle fiber, their function is not to provide structural support. That role is fulfilled by connective tissues like endomysium and cytoskeletal proteins.
Choice C reason: G and F actin are stabilized by proteins like tropomyosin and nebulin, not T tubules. T tubules are involved in electrical signaling.
Choice D reason: This is the correct answer. T tubules are invaginations of the sarcolemma that conduct action potentials deep into the muscle fiber. This ensures that the signal for contraction reaches all parts of the muscle simultaneously, triggering calcium release from the sarcoplasmic reticulum.
Choice E reason: Glucose synthesis occurs in the liver and other tissues via gluconeogenesis. Muscle cells use glucose for energy but do not synthesize it through T tubules.
Correct Answer is B
Explanation
Choice A reason: Granulation tissue forms early in the healing process, not after the bony callus. It precedes the formation of fibrocartilaginous and bony calluses.
Choice B reason: Remodeling of the bony callus is the correct answer. After the bony callus forms, it is gradually reshaped by osteoclasts and osteoblasts to restore the bone’s original structure and strength.
Choice C reason: The fibrocartilaginous callus forms before the bony callus, serving as a temporary bridge between broken bone ends.
Choice D reason: Hematoma formation is the initial step in fracture healing, occurring immediately after injury.
Choice E reason:
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