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BIOC34H3 Chapter Notes -Atropine, Vasodilation, Calcium Channel Blocker

Biological Sciences
Course Code
Stephen Reid

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Farzook Fayyaz
BGYC34; First Assignment (2013)
PhysioEx Lab 6 (Cardiovascular Physiology)
Due Date: Friday, January 25, 2013
Perform the experiments in PhysioEx lab 6 (Cardiovascular Physiology). Provide the
results requested, and answer the questions, for each of the following activities. There are
a total of 25 marks.
Note: The activity names and numbers listed below correspond to those in PhysioEx
version 9.0. If you are using an older version of PhysioEx the exact activity names and
numbers may not match. In this case, identify which activities in the older versions
correspond to the ones listed below and place the appropriate data in the corresponding
Activity 1: Investigating the Refractory Period of Cardiac Muscle
Results: Briefly describe what happened when you applied the electrical stimuli to the
heart. (2 marks)
Applying electrical stimulation to the heart resulted in an extrasystole. During the
extrasystole, the ventricle contracted during relaxation and a bimodal peak (doublet)
appeared on the oscilloscope. Following this, there was a brief halt to allow heart beat to
return to normal
Question 1: Explain why the larger waves seen on the oscilloscope represent ventricular
contraction. (1 mark)
Compared to the atrial muscle, the ventricular muscle is more massive and has to pump
blood over a greater distance (systemic circulation compared with pulmonary circuit). It
also has to contract with a greater force than the atrial muscle does, which is the reason
we see larger waves on the oscilloscope for ventricular contraction. Moreover, the
electrical activity created in the oscilloscope is proportional to muscle mass, which
explains why the atrial depolarization has a smaller wave (atria - less muscle mass)
compared to ventricular depolarization.
Activity 2: Examining the Effect of Vagus Nerve Stimulation
Results: Briefly describe what happened when you electrically stimulated the vagus
nerve. (2 marks)
Upon electrical stimulation of the vagus nerve, the heart rate gradually decreased to the
point where it stopped beating. This phase was known as vagal stimulation. The heart
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