The first heart sound is heard when the A AV valves open B A

The first heart sound is heard when the A) AV valves open. B) AV valves close. C) semilunar valves close. D) atria contract. E) blood enters the aorta. During the isovolumetric contraction phase of ventricular systole, the A) atria are contracting and the ventricles are relaxing. B) atrioventricular valves and semilunar valves are closed. C) Wood is ejected into the great vessels. D) All of the answers are correct. E) None of the answers is correct. Pacemaker cells isolated from the SA node generate action potentials at _______ beats per minute. A) 20-40 B) 40-60 C) 80-100 D) 100-140 E) 140-180 The long plateau phase of the cardiac muscle action potential is due to A) movement of fewer sodium ions across the cell membrane into the cell. B) calcium channels remaining open. C) increased membrane permeability to potassium ion. D) decrease in the amount of calcium diffusing across the membrane. E) increased membrane permeability to sodium ions. As a result of the long refractory period in the cardiac action potential, cardiac muscle cannot exhibit A) tonus. B) treppe C) tetany. D) recruitment. E) fatigue.

Solution

14.B.AV valves close.

The first heart sound is due to the turbulence caused by closing of mitral and tricuspid valves (Atrioventricular valves)

15.Option D. All of the answers are correct.

16.Option C.60-100 beats per minute

17. Calcium channels remaining open.

18. Answer is tetany.