Physioex 6

Topics: Blood pressure, Cardiac muscle, Heart Pages: 5 (1639 words) Published: April 13, 2013
Danielle Rollins

Cardiovascular Physiology
Activity 1
1) Explain why the larger waves seen on the oscilloscope represent ventricular contraction. The ventricular contraction is when the blood is sent through the whole body as opposed to the atrial contraction that sends the blood to the heart and lungs. 2) Explain why the amplitude of the wave did not change when you increased the frequency of the stimulation. (Hint: relate your response to the refractory period of the cardiac action potential) How well did the results compare with your prediction? The threshold doesn’t change because after the voltage was simulated the cardiac muscle cells Ca channels opened. You cannot open them anymore or reopen them before depolarization. This is due to the refractory period. 3) Why is it only possible to induce an extrasystole during relaxation? Because cardiac muscle is able to depolarize after repolarization takes place. 4) Explain why wave summation and tetanus are not possible in cardiac muscle tissue. How well did the results compare to your prediction? Cells do not show tetanus or summation because cardiac cells have both long action potentials and long twitches. Activity 2 1) Explain the effect that extreme vagus nerve stimulation had on the heart. How well did the results compare with your predictions? The heart rate decreases stopping the heart temporarily. 2) Explain two ways that the heart can overcome excessive vagal stimulation. Two ways to overcome excessive vagal stimulation are sympathetic reflexes and initiating the rhythm of the Purkinje Fibers. 3) Describe how the sympathetic and parasympathetic nervous systems work together to regulate heart rate. Sympathetic increases the heart rate whereas Parasympathetic decreases the heart rate. 4) What do you think would happen to the heart rate if the vagus nerve was cut? The heart rate will increase and return back to the 100 bpm. Lab Questions:

1) Cardiac muscle does not undergo temporal summation and it cannot be tetanized. A) Explain the mechanism that prevents the heart from being tetanized. Be sure to refer to the role of calcium ions and channels in your explanation. B) then, explain why it is physiologically important that the heart muscle not undergo complete tetanus. The calcium channels are slowly inactivated causing a long plateau phase of the action potentials in the cardiac muscle. The calcium channels close during the refractory period through to the repolarization phase. Because the channels are closing they cannot be opened again to form tetanus. Because tetanus requires that the muscle be constantly contracted, the cardiac muscle would not be able to have blood flow from taking place in the heart. The cardiac muscle is able to control the blood flow with time increments moving through multiple phases called cardiac cycles. 2) Based on your study of the four drugs that modify heart rate and the readings in PhysioEx, which of the drugs is an agonist of the parasympathetic nervous system? What does being an agonist mean? Acetylcholine. An agonist is when the modifier works in the same way as the neurotransmitter does. 3) The vagus nerve delivers signals from which division of the nervous system? What is the vagal escape, what is its importance, and how might heart rate eventually be restored? The vagus nerve delivers signals from the parasympathetic nervous system to the heart. The vagal escape is the resumption/ beating of the ventricles causing the heart beat to start up again. If the vagus nerve is stimulated(vagal stimulation) to a higher voltage then the heart will stop beating for a short time and the ventricles will then resume with a heartbeat again. The SA node works as a pace maker for the heart when there is an absence of the parasympathetic stimulation, sympathetic stimulation, and hormonal controls. VASCULAR PHYSIOLOGY PART II HOMEWORK

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