Which muscle(s) can contract without the need for nervous stimulation?
Smooth and cardiac muscle
Skeletal, smooth, and cardiac muscle
Cardiac muscle
Skeletal muscle
Smooth muscle
The Correct Answer is A
Choice A reason: Smooth and cardiac muscle are capable of contracting without direct nervous stimulation. Cardiac muscle has intrinsic pacemaker cells that generate rhythmic contractions, and smooth muscle can respond to chemical signals, stretch, and local factors independently of neural input.
Choice B reason: Skeletal muscle requires nervous stimulation to contract. It is under voluntary control and cannot initiate contraction on its own, making this choice incorrect.
Choice C reason: While cardiac muscle can contract independently, this choice omits smooth muscle, which also has autonomous contractile ability. Therefore, it is incomplete.
Choice D reason: Skeletal muscle is entirely dependent on neural input for contraction. It cannot contract without stimulation from motor neurons.
Choice E reason: Smooth muscle can contract without nervous stimulation, but this choice excludes cardiac muscle, which also shares this property. Thus, it is not the best answer.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
Choice A reason: Fast glycolytic fibers are specialized for short bursts of high-intensity activity. They rely on anaerobic metabolism, have large diameters, high glycogen content, and contract rapidly. Sprinting demands explosive power and speed, making these fibers ideal for the task.
Choice B reason: Raking leaves is a moderate-intensity, sustained activity that relies more on slow oxidative or intermediate fibers. It does not require the rapid, forceful contractions characteristic of fast glycolytic fibers.
Choice C reason: Maintaining posture involves continuous, low-intensity contractions, typically supported by slow oxidative fibers. These fibers are fatigue-resistant and suited for endurance, not rapid force generation.
Choice D reason: Hitting a golf ball involves a quick, forceful movement, but it is more reliant on fast oxidative-glycolytic fibers due to the need for both speed and some endurance. It is not as purely anaerobic and explosive as sprinting.
Choice E reason: Running a marathon is a prolonged endurance activity that depends heavily on slow oxidative fibers, which are efficient at aerobic metabolism and fatigue-resistant. Fast glycolytic fibers are not suited for this type of sustained effort.
Correct Answer is D
Explanation
Choice A reason: Actin is a structural protein that forms the thin filaments in muscle fibers. It interacts with myosin during contraction but does not bind calcium directly or initiate contraction.
Choice B reason: Tropomyosin is a regulatory protein that blocks the myosin-binding sites on actin in a relaxed muscle. It shifts position when calcium binds to troponin, but it does not itself bind calcium.
Choice C reason: Titin is a large elastic protein that helps maintain the structural integrity of the sarcomere and contributes to passive elasticity. It does not function as a calcium receptor.
Choice D reason: Troponin is the correct answer. It is a regulatory protein complex that binds calcium ions during muscle contraction. This binding causes a conformational change that moves tropomyosin away from actin’s binding sites, allowing myosin to interact with actin and initiate contraction.
Choice E reason: Dystrophin is a structural protein that connects the cytoskeleton of muscle fibers to the extracellular matrix. It plays a role in muscle integrity but does not bind calcium or regulate contraction.
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