Physio 9.0 exercise 6

Name: Ashlei Sickles
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.
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Review Sheet Results
1. Explain why the larger waves seen on the oscilloscope represent the ventricular contraction.
Your answer:
The ventricular contraction is of greater force than the atrial contraction since the ventricular contraction functions to send blood throughout the entire body (systemic circulation). The contraction of the atrium send blood only to the lungs and rest of the the heart (pulmonary circulation).
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 maximum threshold will not change in cardiac muscle cells, which is determined by the amount of voltage needed for calcium channels to open. After this point, no additional voltage can cause the channels to open more, or again, prior to depolarization. I was wrong in my prediction because I thought it would increase.
3. Why is it only possible to induce an extrasystole during relaxation?
Your answer:
Cardiac muscle is able to depolarize only after repolarization.
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 long action potentials and long twitches, therefore do not show temporal summation. I was wrong because I thought tetanus would occur.