Investigating the Refractory Period of Cardiac Muscle

7/8/2020 PhysioEx Exercise 6 Activity 1 PhysioEx Lab Report Exercise 6: Cardiovascular Physiology Activity 1: Investigating the Refractory Period of Cardiac Muscle Name: Date: 8 July 2020 Pre-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1 The cardiac muscle is capable of which of the following? You correctly answered: autorhythmicity. 2 Phase 2 of the cardiac action potential, when the calcium channels remain open and potassium channels are closed, is called the You correctly answered: plateau phase. 3 Which of the following is true of the cardiac action potential? You correctly answered: The cardiac action potential is longer than the skeletal muscle action potential. 4 The main anatomical difference between the frog heart and the human heart is that the frog heart has You correctly answered: a single, fused ventricle. Experiment Results Predict Questions 1 Predict Question 1: When you increase the frequency of the stimulation, what do you think will happen to the amplitude (height) of the ventricular systole wave? Your answer: The amplitude will increase. 2 Predict Question 2: If you deliver multiple stimuli (20 stimuli per second) to the heart, what do you think will happen? Your answer: neither wave summation nor tetanus. Stop & Think Questions 1/3 7/8/2020 PhysioEx Exercise 6 Activity 1 1 Watch the contractile activity from the frog heart on the oscilloscope. Enter the number of ventricular contractions per minute (from the heart rate display). You answered: 62 beats/min. 2 Which of the following statements about the contractile activity is true? You correctly answered: The smaller waves represent the contraction of the atria. 3 During which portion of the cardiac muscle contraction is it possible to induce an extrasystole? You correctly answered: during relaxation. Experiment Data Post-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1 The amplitude of the ventricular systole did not change with the more frequent stimulation because You correctly answered: a new contraction could not begin until the relaxation phase. 2/3 7/8/2020 PhysioEx Exercise 6 Activity 1 2 Which of the following do you think contribute to the inability of cardiac muscle to be tetanized? You correctly answered: the long refractory period of the cardiac action potential. 3 Given the function of the heart, why is it important that cardiac muscle cannot reach tetanus? You correctly answered: The ventricles must contract and relax fully with each beat to pump blood. 4 An extrasystole corresponds to You correctly answered: an extra ventricular contraction. Review Sheet Results 1 Explain why the larger waves seen on the oscilloscope represent the ventricular contraction. Your answer: because the ventricles of the heart are much stronger than the atria; the ventricles have to pump blood throughout the whole body. 2 Explain why the amplitude of the wave did not change when you increased the frequency of the stimulation. (Hint: relate your response to the refractory period of the cardiac action potential.) How well did the results compare with your prediction? Your answer: The amplitude did not change with frequency because the heart has a long stimulation refractory period i predicted incorrectly. 3 Why is it only possible to induce an extrasystole during relaxation? Your answer: Because the cardiac muscle is only able to depolarize after it repolarizes because of its long refractory period, so the extrasystole is not able to occur until the relaxation period. 4 Explain why wave summation and tetanus are not possible in cardiac muscle tissue. How well did the results compare with your prediction? Your answer: Wave summation and tetanus are not possible in cardiac muscle tissue because cardiac cells have longer action potentials and a very long refractory period compared to other cells. 3/3