A.40mV B.-55mV -65 mV ,85my E.-105mV A 17.If the Purkinje fibers,situated distal to the A-V junction,become the pacemaker of the heart. what is the expected heart rate? 30/min B.50/min C.60/min D.70/min E.80/min 18.Sympathetic stimulation of the heart normally causes which of the following conditions? A.Acetylcholine release at the sympathetic endings B.Decreased heart rate C.Dec eased rate of conduction of the cardiac impulse D.De Increas sed force of contraction of the ventricles A 19.Which of the following statements about cardiac muscle is most accurate? A The t-tubules of cardiac muscle can store much less calcium than t-tubules in skeletal muscle B The strength and contraction of cardiac muscle depends on the amount of calcium surrounding cardiac myocytes C.In cardiac muscle the initiation of the action potential causes an immediate opening of slow calcium channels D.Cardiac is caused by opening of sodium channels Mucopolysaccharides inside the T-tubules bind chloride ions 20. Which of the following is most likely to cause the heart to go into spastic contraction? A.Increased body temperature Decreased Excess extracellular fluid potassium ions E.Excess extracellular fluid calcium ions E 21.Which of the following events occurs at the end of the period of ventricular ejection? A A-V valves close B Aortic valve opens Aortic valve remains open D.A-V valves open E.Pulmonary valve closes A. -40 mV B. -55 mV C. -65 mV D. -85 mV E. -105 mV A 17. If the Purkinje fibers, situated distal to the A-V junction, become the pacemaker of the heart, what is the expected heart rate? A. 30/min B. 50/min C. 60/min D. 70/min E. 80/min A 18. Sympathetic stimulation of the heart normally causes which of the following conditions? A. Acetylcholine release at the sympathetic endings B. Decreased heart rate C. Decreased rate of conduction of the cardiac impulse D. Decreased force of contraction of the atria E. Increased force of contraction of the ventricles A 19. Which of the following statements about cardiac muscle is most accurate? A. The T-tubules of cardiac muscle can store much less calcium than T-tubules in skeletal muscle B. The strength and contraction of cardiac muscle depends on the amount of calcium surrounding cardiac myocytes C. In cardiac muscle the initiation of the action potential causes an immediate opening of slow calcium channels D. Cardiac muscle repolarization is caused by opening of sodium channels E. Mucopolysaccharides inside the T-tubules bind chloride ions B 20. Which of the following is most likely to cause the heart to go into spastic contraction? A. Increased body temperature B. Increased sympathetic activity C. Decreased extracellular fluid potassium ions D. Excess extracellular fluid potassium ions E. Excess extracellular fluid calcium ions E 21. Which of the following events occurs at the end of the period of ventricular ejection? A. A-V valves close B. Aortic valve opens C. Aortic valve remains open D. A-V valves open E. Pulmonary valve closes