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Circulatory / Respiratory › View

What causes the semilunar valves to open?

A. contraction of the ventricles

B. contraction of the atria

C. stimulation of the SA node

D. backflow of blood in the aorta and pulmonary artery during diastole

E. contraction of the cardiac muscle that makes up the valves

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Anatomy › View

What cell organelle provides ATP needed for muscle activity

A. Acetylcholine

B. Mitochondria

C. Perimysium

D. Myosin

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