What would happen if your SA node and AV node fired at same time?
A. The QRS wave on an ECG would disappear, as it would be masked by the P wave.
B. Your blood pressure would increase.
C. The production of nitric oxide by your endothelial cells would increase.
D. Blood would be forced back into the atria from the ventricles.
E. Your stroke volume would decrease.
Clarify Question
What is the key concept addressed by the question?
What type of thinking is required?
Gather Content
What do you already know about the SA and AV nodes? What other information is related to the question?
Choose Answer
Given what you now know, what information is most likely to produce the correct answer?
Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
E. Your stroke volume would decrease.
Clarify Question
What is the key concept addressed by the question?
· The question is asking about the effects of firing the SA and AV nodes.
What type of thinking is required?
· Analyze level:
o This is an analyze question because you have to break the musculature of the left and right ventricles into their component pieces to understand how they function.
Gather Content
What do you already know about the SA and AV nodes? What other information is related to the question?
· An electrocardiogram (ECG) records the electrical activity of the heart.
· The P wave shows the depolarization/contraction of the atria.
· The depolarization/contraction of the ventricles is shown in the QRS wave. The repolarization of the atria is masked by this wave.
· The T wave represents the repolarization of the ventricles.
· A normal heartbeat requires the flow of an impulse throughout the heart.
· The initiation of a heartbeat occurs in the sinoatrial (SA) node located in the right atrium.
· The SA node is the pacemaker of the heart.
· The SA node initiates the depolarization of the atria.
· The action potential from the SA node travels via the internodal pathway to the atrioventricular node.
· The impulse travels from the AV node to the bundle branches, and then to the Purkinje fibers where it is dispersed through the ventricles.
· To beat efficiently, the atria contract to fill the ventricles.
· The ventricles are relaxed as the atria contract, which allows a maximum amount of blood to enter the ventricles.
Choose Answer
Given what you now know, what information is most likely to produce the correct answer?
· The P wave is smaller than the QRS wave, so the QRS wave would not be masked.
· As long as the atrioventricular valves are working properly, blood will not flow from the ventricle back into the atria.
· If the SA and AV nodes fire at the same time, the atria and ventricles would depolarize at the same time. Since the atria normally fill the ventricles by contracting when the ventricles are relaxed, this simultaneous firing of the SA and AV nodes would result in less full ventricles and lower blood pressure. Since less blood would be present in the ventricles, stroke volume would also be lower in this case.
· Nitric oxide acts to relax the walls of blood vessels when blood pressure is high, which would not be needed in this situation.
Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
· Analyze level:
o Answering this question correctly depended not only on distinguishing between the actions of the SA and AV nodes, but on your ability to break down, or analyze, the consequences of their simultaneous activity. If you got an incorrect answer, did you remember that components of firing the SA node include the depolarization of the atria, or that the firing of the AV node would likely affect cause blood to leave the ventricles before they were full? Did you have trouble breaking down the actions of the SA and AV nodes to determine the correct answer?
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