ACTIVITY 1: Investigating the Refractory Period of
Cardiac Muscle Answers
1. Which of the following types of muscle tissue can depolarize spontaneously in the absence of any external stimulation:
a. Skeletal muscle
b. Smooth muscle
c. Cardiac muscle
d. All of the above
2. Look at Figure 6.1, the cardiac action potential. The period of time between the beginning of the cardiac action potential and the approximate middle of phase 3 is the __________________ refractory period of cardiac muscle.
3. In this simulation, when you delivered several single stimuli very rapidly, you saw a double peak. The second peak is called an ______________.
4. True or False: In order for the heart to function the most effectively in pumping blood, the ventricles must contract and then relax fully with each beat. False
5. Explain why the larger waves seen on the oscilloscope represent ventricular contractions.
6. 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.)
7. Why is it only possible to induce an extra systole during relaxation. It is possible to induce an extrasystole in the relaxation part of the cardiac cycle.
8. Explain why wave summation and tetanus are not possible in cardiac muscle tissue. The heart cannot be tetanized by multiple stimuli. Tetanization would make the heart ineffective as a pump.
ACTIVITY 2: Examining the Effect of Vagus Nerve Stimulation
9. Cranial nerve 10, the vagus nerve, is an important part of which nervous system…the sympathetic or parasympathetic?
10. True or False: Both the sympathetic nervous system and the parasympathetic nervous system can cause the heart rate to change and affect the strength of contraction of the heart.
11. In this simulation, at rest the frog heart was “beating” at ______ beats/minute. After stimulation with the vagus nerve at 50 times/minute, the heart rate ___________.
12. Both the vagus nerve and a branch of the sympathetic nervous system innervate the
a. heart muscle.
b. sinoatrial (SA) node.
c. bundle of His.
d. Purkinje fibers.
13. Explain the effect that extreme vagus nerve stimulation had on the heart.
14. The SA node of the heart is located in the ______ _______.
15. Describe how the sympathetic and parasympathetic nervous systems work together to regulate the heart rate.
16. What do you think would happen to the heart rate if the vagus nerve were surgically cut?
ACTIVITY 3: Examining the Effect of Temperature on Heart Rate
17. Humans are _________________, i.e. are able to maintain an internal body temperature within a small temperature range even though the external temperature is changing.
18. When 5 degree C Ringer’s solution was “dripped” on the heart, the heart rate stabilized at ______ beats/minute; when 32 degree C Ringer’s solution was used, the heart rate stabilized at ______ beats/minute.
19. If an infant developed a fever of 40 degrees C (104 degrees F), its heart rate would probably
a. stay the same as when there was no fever.
b. decrease.
c. increase.
d. stop completely.
20. Explain the effect that decreasing the temperature had on the frog heart. How do you think the human heart would respond?
21. Describe why Ringer’s solution is required to maintain heart contractions.
22. Explain the effect that increasing the temperature had on the frog heart rate. How do you think the human heart would respond?
ACTIVITY 4: Examining the Effects of Chemical Modifiers on Heart Rate
23. Chemical modifiers that inhibit, mimic, or enhance the action of the neurotransmitter acetylcholine in the body are labeled _________________________.
24. If the modifier works in the same fashion as the neurotransmitter, it is an ____________. If it works I opposition to the neurotransmitter, it is an _______________.
25. The frog’s heart, at rest, was about 61 beats/minute (BPM). When epinephrine was “dripped” on the heart, the rate changed to _____ BPM; when pilocarpine was dripped on the heart, the rate changed to _____ BPM.
a. 40; 100
b. 65; 55
c. 81; 46
d. 90; 32
26. True or False: A ?-1 receptor can bind both epinephrine and norepinephrine.
27. Describe the effect that pilocarpine had on the heart and why it had this effect.
28. Atropine is an “acetylcholine antagonist.” Does atropine inhibit or enhance the effects of acetylcholine? ____________ Describe your results and how they correlate with how the drug works.
29. Describe the benefits of administering digitalis.
30. Distinguish between cholinergic and adrenergic chemical modifiers. Include examples of each in your discussion.
ACTIVITY 5: Examining the Effects of Various Ions on Heart Rate
31. As discussed in your lab manual, any ion or chemical that affects the heart rate is called ________; an ion or chemical that affects the force of contraction is called _______.
32. The resting cardiac muscle cell favors the movement of which ion more than others?
a. potassium
b. sodium
c. calcium
d. magnesium
33. When calcium was “dripped” on the frog’s heart, the heart rate changed to ______ BPM .
34. True or False: Calcium ions had the most pronounced effect on heart rate compared to potassium or sodium.
35. Describe the effect that increasing the potassium had on the heart in this activity. How did this change the resting membrane potential of the cardiac muscle cell?
36. Describe how medicines called “calcium channel blockers” are used to treat patients and why?
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