AP Biology : Understanding Electrical Stimulation in the Heart
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Example Question #1 : Cardiac Physiology
The sinoatrial node generates action potentials at a faster pace than normal heart rate. Why does the heart beat more slowly than the SA node would dictate?
The atrioventricular node requires multiple action potentials in order to continue the electrical signal through the heart.
Many of the action potentials are not large enough to cause a contraction of the heart.
The parasympathetic vagus nerve slows down the heart rate.
Half of the action potentials are dedicated to the contraction of the atria, and the other half are dedicated to the contraction of the ventricles.
The parasympathetic vagus nerve slows down the heart rate.
The vagus nerve is responsible for slowing down the heart rate, and is able to "override" the faster, natural pace of the sinoatrial node. When the vagus nerve is severed from the heart, the heart will pump at the pace of the SA node.
Note that innervation is not necessary for the heart to continue beating; it is self-sustaining, but can be affected by innervation from the vagus nerve.
Example Question #2 : Understanding Electrical Stimulation In The Heart
Which of the following structures is NOT part of the cardiac conducting system?
Chordae tendinae
Purkinje fibers
Sinoatrial node
Atrioventricular bundle
Chordae tendinae
The chordae tendinae (tendinous chords or heart strings) are physical structures located in the heart lumen that connect the muscular wall of the heart to the tricuspid and mitral valves via papillary muscles.
The other answer options are examples of cell bundles and tissues that orchestrate the electrical conduction through the heart. Signals begin at the sinoatrial node and transition to the atrioventricular node. They then pass through the atrioventricular bundle (or bundle of His) to the purkinje fibers, which coordinate simultaneous ventricular contraction.
Example Question #51 : Circulatory System
What is the importance of the atrioventricular node's time delay upon receiving impulses from the sinoatrial node?
It allows the atria to adequately fill with blood
It allows the ventricles to adequately fill with blood
It gives the cardiac cells time to depolarize
It allows the impulse to spread evenly throughout the heart
It allows the ventricles to adequately fill with blood
The sinoatrial node is responsible for initiating the contraction of the heart. Depolarization of the sinoatrial node coincides with atrial contraction. The depolarization travels very quickly to the atrioventricular node during this period. The atrioventricular node delays the spread of the impulse, preventing it from triggering ventricular contraction. This time delay allows the atria to fill the ventricles with blood before the impulse causes the ventricles to contract. Without this delay, an inadequate amount of blood would be pumped from the ventricles.
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