BIOC34H3 Lecture Notes - Vagus Nerve, Pilocarpine, Digitalis

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Published on 7 Jul 2012
School
UTSC
Department
Biological Sciences
Course
BIOC34H3
Professor
Introduction [
/2]
Write a brief (no more than 100 words) introduction that describes the goal of the experiments
performed in this lab. (2 marks)
Heart rate is the number of heart beats per minute. The heart rate is based on the number of
contractions of the ventricles in a certain period of time. Throughout this experiment, the frog heart will
be put under various circumstances in order to see their effects on the heart rate. These circumstances
include: electrical stimulations at different locations of one wave, constant electrical stimulation for a
period of time, and the effects of various drugs, hormones and as well as temperature. The heart rate is
expected to change accordingly in each situation due to underlying physiological mechanisms.
Methods
[ /3]
Write a brief (no more than 300 words) methods section that describes the experiments performed in
this lab. Describe the experimental preparation and the various manipulations that were performed. (3
marks)
During the direct heart stimulation, an electrode was placed touching the heart. A single
stimulus was given to the heart at the beginning of ventricular contraction, at the peak of ventricular
contraction and during the fall of ventricular contraction. The affects of the stimulation at the different
phases was observed. Also using the same electrode, multiple stimuli, 20 stimuli/sec, was given for a
few seconds and the effects were observed.
The electrode that was used previously was replaced with the Vagus Nerve Stimulation
electrode. Attached to the tip of the electrode was the Vagus Nerve, which made contact with the heart.
Every time a stimulus was given through the electrode; it will indirectly stimulate the heart through the
Vagus nerve. The Vagus nerve was stimulated at 50 stimuli/sec for 70 seconds. Observations were
recorded for the change in heart rate and the change in the ECG waves for 90 seconds. The Vagus
nerve was then given 50 stimuli/sec until the Heart Rate was stable and the Heart Rate was recorded.
This was repeated with 40, 30, 20 and 10 stimuli/sec to see at what rate the heart rate stabilized.
The next experiment was to see the effects of various drugs, hormones and ions on heart rate.
The frog heart was first bathed with 23°C Ringers solution and the Heart Rate was
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recorded once it reached its normal stage. Next, the a couple drops of epinephrine was let
to fall on the heart. The heart rate was left to stabilize and the Heart Rate was recorded. The same
procedure was repeated with Pilocarpine, Atropine, Digitalis, Calcium, Sodium and Potassium Ions.
Results
1. Direct Electrical Stimulation of the Heart
[ /1]
Figure 1: Trace of heart rate with no electrical stimulation
Figure 2: Trace of heart rate with a single electrical stimulation delivered at the beginning of the
ventricular contraction.
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Figure 3: Trace of heart rate with a single electrical stimulation delivered near the peak of the
ventricular contraction.
Figure 4: Trace of heart rate with a single electrical stimulation delivered during the “fall” of
ventricular contraction.
Figure 5: Trace of heart rate with multiple stimuli delivered at a rate of 20 stimuli per second.
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Document Summary

Write a brief (no more than 100 words) introduction that describes the goal of the experiments performed in this lab. (2 marks) Heart rate is the number of heart beats per minute. The heart rate is based on the number of contractions of the ventricles in a certain period of time. Throughout this experiment, the frog heart will be put under various circumstances in order to see their effects on the heart rate. These circumstances include: electrical stimulations at different locations of one wave, constant electrical stimulation for a period of time, and the effects of various drugs, hormones and as well as temperature. The heart rate is expected to change accordingly in each situation due to underlying physiological mechanisms. Write a brief (no more than 300 words) methods section that describes the experiments performed in this lab. Describe the experimental preparation and the various manipulations that were performed. (3 marks)

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