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BIOC34H3 (114)


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University of Toronto Scarborough
Biological Sciences
Stephen Reid

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 1 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. 2 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. 3 2a. Vagus Nerve Stimulation [ /2] Time Period HR HR Status Observation (normal, stable or changing) Pre Stimulus • Regular ECG waves were seen 60 normal • Atrial contraction and ventricular contraction were clearly visible • All waves were of equal height and length • Heart rate decreased drastically 10 s post stimulus 28 changing • Large compensatory pauses were seen • Waves started to get larger • P-R distance increased dramatically as seconds increased • A short period of baseline activity was seen 20 s post stimulus --- --------- • No waves were present at all • Absence of heart rate • Baseline activity started to decrease 30 s post stimulus 19 changing • The line started to take form of wave shape • Heart rate started to pick up pace again 40 s post stimulus 44 changing • Started to increase slowly • Waves started to take shape of original waves • Length of each wave started to shorten • Regular forms of waves were seen 50 s post stimulus 49 changing • Waves seemed to be wider than normal conditions • P-R distance was obviously greater than that of normal waves • The waves were similar to the waves seen 60 s post stimulus 51 stable under normal conditions • The length of the waves looked a little bit longer than that of normal waves • The waves still remained to be the same 70 s post stimulus 53 stable from the previous observations • Nothing new was seen 10 s after stopping • Heart rate quickly sprung up to 61 stimulus 60 Normal • ECG waves were back to normal height and length 20 s after stopping 60 normal • Same wave forms existed from previous stimulus period of observation 4 • Waves were consistent 2a. Vagus Nerve Stimulation: Effects of Altered Stimulation Frequency [ /2] Stimulus HR upon Observation Rate stabilisation (stimuli/sec) 51 • Heart rate decreased drastically 50 • After 20 bpm, there was a period of just baseline activity • A compensatory pause was observed between adjacent ECG waves 19 • heart rate decreased smoothly 40 • Lowest heart rate seen was 19bpm • Long compensatory pauses were observed • No period of baseline activity was seen • ECG waves increased in size 29 • heart rate decreased at a constant pace 30 • 29 was the lowest bpm observed • The distance between P & R increased in size as heart rate decreased 40 • Lowest heart rate observed was 40 bpm 20 • The P & R distance increased compared to it’s
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