Yu Cardiac APs
Terms
- How can pacemaker activity, conduction velocity, and contractility be affected?
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-Inc. steepness; lengthen time for Vm to reach threshold; Heart rate falls (diastole longer)
-Max diastolic potential, more negative, lower Vm
-Inc. threshold, longer to reach threshold
- How does Acetylcholine affect the pacemaker?
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(Parasympathetic) releases ACh to SA and AV nodes. AV: to slow conduction; harder to depolarize neighbors
-Decreases If, reducing steepness
-Open GIRK channels, increase K conductance; make max diastole
-Reduce Ica= reduce steep; thre
- How does catecholamines affect the pacemaker?
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Sympathetic: NE;Adrenal medulla: E; beta-1 receptors
Increase If: inc. steepness
Inc Ica everywhere: inc steepness; threshold more negative
in muscle: increase Ca; stronger contraction
- How does voltage change from cell to cell?
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It becomes progressively smaller further from the source.
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Upstroke speeds of the heart.
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Slow: AV, SA nodes
Fast: artial and ventricular muscles, Purkinje fibers
- What can modulate how the pacemaker works?
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Acetylcholine Catecholamine
- What does the voltage change from cell to cell mean?
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An AP in the neighbor can be triggered. Even further down.
More cells brought to threshold
AP will propagate faster.
- What's overdrive suppression?
- The fastest inherent beat rhythms act as "pacemakers" and impose their rhythm on the other cells.
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What's the path of an AP?
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SA node in right atrium -> through the right atrium -> through left atrium -> His-Purkinje fiber system -> both ventricles.
- What's the primary pacemaker?
- SA node
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Why doesn't the AP go directly from the atria to the ventricles?
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Because of a fibrous atrioventricular ring.
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Why is there so much Ca released in the cardiac muscle?
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Ca entering L-type Ca channels activate Ca from SR:
Ca-induced Ca release.