[PhysioEX Chapter 6 exercise 2] PEX-06-02

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Exercise 6: Cardiovascular Physiology: Activity 2: Examining the Effect of Vagus Nerve Stimulation Lab Report

Pre-lab Quiz Results
You scored 100% by answering 4 out of 4 questions correctly.

1. The effect of the parasympathetic nervous system on the heart is to
   You correctly answered: a. decrease the heart rate.
2. The branch of the autonomic nervous system that dominates during exercise is
   You correctly answered: b. the sympathetic branch.
3. Parasympathetic stimulation reaches the heart through
   You correctly answered: d. vagus nerves, which are cranial nerves.
4. The usual pacemaker of the heart
   You correctly answered: c. is the sinoatrial node.

Experiment Results

Predict Question:
Predict Question: What do you think will happen if you apply multiple stimuli to the heart by indirectly stimulating the vagus
nerve?
Your answer : c. The heart rate will decrease and the heart will stop.

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: 59 beats/min
   The vagus nerve carries
   You correctly answered: a. signals that decrease the heart rate.
2. 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: 59 beats/min
   The response that resumed the heartbeat after the vagus nerve stimulation is called
   You correctly answered: b. vagal escape.
   Experiment Data:

Post-lab Quiz Results
You scored 100% by answering 4 out of 4 questions correctly.

1. Extreme vagus nerve stimulation affects the heart by
   You correctly answered: a. stopping the heart completely.
2. Vagal escape probably involves
   You correctly answered: c. sympathetic reflexes.
3. Research shows that, in the absence of neural and hormonal influences, the SA node generates action potentials at a
   frequency of approximately 100 times per minute. However, the resting heart rate is approximately 70 beats per minute,
   which suggests that
   You correctly answered: b. the parasympathetic nervous system has more control over heart rate.
4. The SA (sinoatrial) node in the human heart is located
   You correctly answered: c. in the right atrium

Review Sheet Results

1. Explain the effect that extreme vagus nerve stimulation had on the heart. How well did the results compare with your
   prediction?
   Your answer:
   The heart rate surely decreased and after all the heart stopped as I predicted.
2. Explain two ways that the heart can overcome excessive vagal stimulation.
   Your answer:
   First, Sympathetic reflexes. Second, initiation of a rhythm by the Purkinje Fibers
3. Describe how the sympathetic and parasympathetic nervous systems work together to regulate heart rate.
   Your answer:
   The sympathetic nervous system increases heart rate and parasympathetic decreases heart rate.
4. What do you think would happen to the heart rate if the vagus nerve was cut?
   Your answer:
   Then the heart rate would increase, then back to 100 BPM.