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27 Cards in this Set
- Front
- Back
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What initiates contraction of the heart
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Action potentials; along with EC coupling
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Which contract first the atria or ventricles
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Atria
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Why does the atria contract, then the ventricles?
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Because of the sequence of electrical excitation
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What are some examples of myocytes that are able to initiate contraction?
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SA node, AV node, Purkinje fibers
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Describe the following wave form for the given contraction:
Sino-atrial Atrial AV Node Purkinje |
SA - slow response
Atrial - rapid depolarization AV node - slow (all together) Purkinje - fast depolarization, slow repolarization |
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What is the heart beat initiated by?
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Spontaneous depolarization of the SA node
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(T or F) The SA node diastolic depolarization is fast
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False, its slow
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What are some mechanisms that contribute to the slow diastolic depolarization?
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Inward K+ channel is not operating
If channels (funny) channels causing sodium to enter the cell (depolarization) I background - Ca++ out--->in |
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The firing rate of the SA node is modulated by?
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The autonomic nervous system
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What effects do the sympathetic and parasympathetic nervous systems have in the heart?
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Sympathetic - increasing firing rate by increasing If channel activity
Parasympathetic - prolongs time of depolarization by increasing I K+ACh channels and decreasing If channels |
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What are the three pace makers of the heart?
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SA node, AV node, Purkinje fibers
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By what mechanism does the SA node 'pace' the heart?
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Override suppression of the other pacemakers
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What is the order of "quickness" of the pacemakers?
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SA>AV>Purkinje fibers
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If the SA node is damaged the AV node will take over as the pacemaker
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BLANK
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Where is the SA node located?
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Right atrium
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What is the speed of excitation of the SA node across the atria?
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0.05-->1.0 m/s
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How does the excitation proceed from the atria to the ventricles?
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AV node
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What is the benefit of having a slow speed of conduction of the AV node?
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It creates a delay in ventricular excitation
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What is an AV block?
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The slow nature of the AV conduction allows for coordinated heartbeat (like a safety valve)
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What is the AV nodal conduction dependent on?
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Voltage gated Ca++ channels
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What is the order of conductors in the ventricles that receive the excitation?
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Bundle of His, bundle branches, Purkinje fibers
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Which ventricle gets its own bundle of His?
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Left ventricle
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How many phases does ventricular action potential's have?
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4:
Rest Depolarization Plateau Repolarization Rest |
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Describe which ion currents are active in all four phases of ventricular contraction
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Rest - K1 inward rectifier
Depolarization - INa in Repolarization - K+ out, Cl- in via Ito channels Plateau - ICa++ channels, late INa+ channels, K+ out Repolarization (late) - K+ efflux/rapid repolarization Rest - K+ channels closed |
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By which means (active or passive) is current spread through ventricular tissue
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passive
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What allows the passive current to pass from one cardiac cell to the other?
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Gap junctions contained within interclated discs
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How is re-excitation of the atria by ventricular depolarization prevented?
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Anulus fibrosus cordis - acts like an insulator between atria and ventricle
AV refractoriness |
