What role does ATP play in the muscle contraction cycle?
It directly causes the initial calcium release from the sarcoplasmic reticulum
It expands the H band by pushing thick filaments apart
It prevents the troponin-tropomyosin complex from exposing binding sites
It binds to mysoin heads, allowing them to detach from actin
The Correct Answer is D
A. It directly causes the initial calcium release from the sarcoplasmic reticulum: Calcium release from the sarcoplasmic reticulum is triggered by depolarization of the T-tubules and activation of ryanodine receptors, not directly by ATP. ATP provides energy for the mechanical steps of contraction but does not initiate calcium release.
B. It expands the H band by pushing thick filaments apart: The H band changes length passively as thin filaments slide over thick filaments during contraction. ATP does not mechanically push filaments apart; instead, it energizes myosin heads for cross-bridge cycling.
C. It prevents the troponin-tropomyosin complex from exposing binding sites: The troponin-tropomyosin complex blocks actin binding sites in the absence of calcium. ATP does not regulate this exposure; calcium binding to troponin shifts tropomyosin to allow myosin attachment.
D. It binds to myosin heads, allowing them to detach from actin: ATP binds to the myosin head after the power stroke, causing detachment from actin and breaking the actomyosin cross-bridge. ATP hydrolysis then re-cocks the myosin head, storing energy for the next contraction cycle. This is essential for continuous muscle contraction and relaxation in both skeletal and cardiac muscle.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is {"dropdown-group-1":"A","dropdown-group-2":"B","dropdown-group-3":"C"}
Explanation
Correct answer:
- J: Pulmonary veins
- G: Right ventricle
- D: Pulmonary trunk
J: Pulmonary veins- Pulmonary veins are blood vessels that carry oxygenated blood from the lungs to the left atrium of the heart. Normally, there are four pulmonary veins—two from each lung. They enter the posterior aspect of the left atrium and play a vital role in systemic circulation by delivering oxygenated blood for distribution throughout the body.
G: Right ventricle- The right ventricle is the lower right chamber of the heart responsible for pumping deoxygenated blood to the lungs for oxygenation. It receives blood from the right atrium through the tricuspid valve and ejects it into the pulmonary artery via the pulmonary valve. It generates enough pressure to move blood through the pulmonary arteries to the lungs, where carbon dioxide is exchanged for oxygen.
D: Pulmonary trunk- The pulmonary trunk is a large artery that carries deoxygenated blood from the right ventricle to the lungs. It begins at the pulmonary valve and extends upward before dividing into the right and left pulmonary arteries. It is located anterior to the ascending aorta and it transports blood to the lungs for gas exchange.
Correct Answer is B
Explanation
N: Pulmonary valve- The pulmonary valve is a semilunar valve between the right ventricle and pulmonary artery. It prevents backflow into the ventricle during diastole, facilitating blood flow toward the lungs for oxygenation.
E: Fossa ovalis - The fossa ovalis is a shallow, thumb-sized depression located in the interatrial septum (the wall separating the right and left atria). In a developing fetus, the foramen ovale is an open "tunnel" that allows blood to bypass the lungs by flowing directly from the right atrium to the left atrium. Once a baby takes their first breath, the pressure changes in the heart cause a flap of tissue to close over this opening. Over time, it fuses shut, leaving behind the shallow indensee fossa ovalis.
O: chordae tendinae: Chordae tendineae are fibrous cords connecting the atrioventricular valve leaflets (mitral and tricuspid) to papillary muscles. They prevent valve prolapse during ventricular contraction, ensuring unidirectional blood flow.
J: Aortic arch- The aortic arch is the curved portion of the aorta that distributes oxygenated blood from the left ventricle to systemic arteries. It contains baroreceptors and helps regulate blood pressure.
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