Electrical Stimulation
Activity 1: Direct Heart Stimulation
1. Did you see any change in the trace?
2. Why or why not?
3. Did you see any change in the trace?
4. Why or why not?
5. Describe the change you see in the trace. How does it differ from the baseline trace?
6. What effect do the repeated stimuli have on the heartbeat trace? Describe the trace.
7. What part of the trace shows the refractory period?
8. Does summation occur?
9. Why is it important that summation not occur in heart muscle?
Activity 2: Vagus Nerve Stimulation
1. Describe the effect of the vagus nerve stimulation on the heartbeat.
2. Soon after you applied the stimuli, did the heart rate increase or decrease?
3. Why?
4. How do the sympathetic and parasympathetic nervous systems work together to regulate heart rate?
5. Complete the following: As heart rate decreases, cardiac output _______ (assuming stroke volume remains the same). As heart rate increases, cardiac output ________ (assuming stroke volume remains the same).
6. What does this tell you about the parasympathetic nervous system in relation to the sympathetic nervous system and hormones?
Modifiers of Heart Rate
Activity 3: Effect of Epinephrine
1. What was the effect of epinephrine on heart rate?
2. Does this effect mimic the effect of the sympathetic nervous system or that of the parasympathetic nervous system?
3. What is the heart rate when the status window reads Heart Rate Stable?
Activity 4: Effect of Pilocarpine
1. What was the effect of pilocarpine on heart rate?
2. What is the heart rate when the status window reads Heart Rate Stable?
Activity 5: Effect of Atropine
1. What was the effect of atropine on heart rate?
2. What is the heart rate when the status window reads Heart Rate Stable?
3. If you were to administer drops of pilocarpine to the heart and then administer atropine immediately afterward, what effect would you expect to see on the heart rate?
Activity 6: Effect of Digitalis
1. What was the effect of digitalis on heart rate?
2. What is the heart rate when the status window reads Heart Rate Stable?
3. Why might digitalis be used on a patient with such a condition?
Activity 7: Effect of Temperature
1. What was the effect of temperature on the frog’s heart rate?
Activity 8: Effects of Ions
1. What was the effect of calcium ions on heart rate?
2. Why?
3. Where in a heart cell is calcium normally found?
4. What was the effect of sodium ions on heart rate?
5. Why?
6. Where in a heart cell is sodium normally found?
7. What was the effect of potassium ions on heart rate?
8. Why?
9. Where in a heart cell is potassium normally found?
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