[PhysioEX Chapter 6 exercise 1] PEX-06-01

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Exercise 6: Cardiovascular Physiology: Activity 1: Investigating the Refractory Period of Cardiac Muscle Lab Report

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: c. 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: a. plateau phase.
3. Which of the following is true of the cardiac action potential?
   You correctly answered: b. 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: c. a single, fused ventricle.

Experiment Results

Predict Question:
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 : c. The amplitude will not change.

Predict Question 2: If you deliver multiple stimuli (20 stimuli per second) to the heart, what do you think will happen?
Your answer : d. neither wave summation nor tetanus

Stop & Think Questions:

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) in the field below and then click
   Submit to record your answer in the lab report.
   You answered: 61 beats/min
   Which of the following statements about the contractile activity is true?
   You correctly answered: a. The smaller waves represent the contraction of the atria.
   During which portion of the cardiac muscle contraction is it possible to induce an extrasystole?
   You correctly answered: d. 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. a new contraction could not begin until the relaxation phase
2. Which of the following do you think contribute to the inability of cardiac muscle to be tetanized?
   You correctly answered: a. 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: b. The ventricles must contract and relax fully with each beat to pump blood.
4. An extrasystole corresponds to
   You correctly answered: c. an extra ventricular contraction.

Review Sheet Results

1. Explain why the larger waves seen on the oscilloscope represent the ventricular contraction.
   Your answer:
   Because ventricle contraction is strengther than atrial contraction.
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:
   Amplitude did not change because of the cardiacs long refractory period, as predicted.
3. Why is it only possible to induce an extrasystole during relaxation?
   Your answer:
   The extrasystole can not occur until relaxation and so we could not achieve wave summation tetanus.
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:
   Cardiac cells have longer twitches than any other muscle cells. As I correctly predicted the cardiac muscle tissue did not
   show neither wave summation nor tetanus.