BGYC34_physioex_lab_6_assigment_2013, due Jan 25.doc

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University of Toronto Scarborough
Biological Sciences
Stephen Reid

1 Farzook Fayyaz 998441397 LEC60 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 section. 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 2 then underwent vagal escape where it resumed its regular beating. This was due to sympathetic reflexes. Question 2: Explain how possible mechanisms of vagal escape would differ in an isolated heart preparation such as the one used in this experiment versus a heart in a live animal/human. (3 marks) In an isolated heart, we wouldn’t be able to get vagal escape because we would not be receiving any regulatory input from the sympathetic system of the central nervous system (associated with brain/spinal cord). Since the heart was isolated from body, vagal escape would not be possible in such a preparation. Additionally, in a live animal/human, we rarely would see the heart shut down completely like it did upon electrical stimulation and vagal escape would not occur very often. Activity 3: Examining the Effect of Temperature on Heart Rate Results: Provide the heart rate values recorded when the heart was bathed with Ringer’s solution of different temperatures. (2 marks) Question 3: Homeothermic animals such as humans have a thermoneutral zone (i.e., a range of external environmental temperatures) in which internal body temperature remains at a constant level while simultaneously maintaining metabolic rate (i.e., energy expenditure) constant. If the e
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