The cross-bridge cycling involves:
Myosin heads pulling actin toward the middle
The shortening of thick filaments so that thin filaments slide past
Actin and myosin lengthening in order to slide past each other
The Z discs sliding over the myofilaments
The protein titin shortening the myosin filament
The Correct Answer is A
Choice A reason: Myosin heads pulling actin toward the center of the sarcomere is the core mechanism of cross-bridge cycling. This interaction shortens the sarcomere and generates muscle contraction. ATP binding and hydrolysis drive the cycle of attachment, power stroke, and detachment.
Choice B reason: Thick filaments do not shorten during contraction. Instead, thin filaments slide past the thick filaments as the sarcomere shortens. The filaments themselves remain the same length.
Choice C reason: Actin and myosin do not lengthen during contraction. They maintain their structural integrity while sliding past each other through repeated cross-bridge interactions.
Choice D reason: Z discs define the boundaries of a sarcomere and move closer together during contraction, but they do not slide over myofilaments. Their movement is a result of filament sliding, not a direct action.
Choice E reason: Titin is a structural protein that contributes to passive elasticity and sarcomere stability. It does not actively shorten or participate in the cross-bridge cycle
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
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.
Correct Answer is A
Explanation
Choice A reason: The sarcomere is the smallest contractile unit of a skeletal muscle. It is composed of actin and myosin filaments arranged in a precise pattern that allows for muscle contraction. Sarcomeres are repeated along the length of a myofibril and are responsible for the striated appearance of skeletal muscle.
Choice B reason: The sarcoplasmic reticulum is a specialized form of endoplasmic reticulum in muscle cells that stores and releases calcium ions, which are essential for muscle contraction. However, it is not the contractile unit itself.
Choice C reason: The sarcolemma is the plasma membrane of a muscle fiber. It plays a role in conducting electrical signals but is not the structural unit responsible for contraction.
Choice D reason: A myofibril is a long, cylindrical organelle found within muscle cells that contains many sarcomeres. While it contributes to muscle contraction, it is composed of multiple sarcomeres and is not the fundamental unit.
Whether you are a student looking to ace your exams or a practicing nurse seeking to enhance your expertise , our nursing education contents will empower you with the confidence and competence to make a difference in the lives of patients and become a respected leader in the healthcare field.
Visit Naxlex, invest in your future and unlock endless possibilities with our unparalleled nursing education contents today
Report Wrong Answer on the Current Question
Do you disagree with the answer? If yes, what is your expected answer? Explain.
Kindly be descriptive with the issue you are facing.