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14 Cards in this Set
- Front
- Back
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Where is the SA node?
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In the superior RA at the junction with the SVC
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True/False: The atrium and the ventricles are insulated from each other
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TRUE--the only electrical connection is the AV node
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How does the Bundle of His relate to the purkinje fibers? Where does one begin and another end?
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The bundle of His and the fascicles end in purkinje cells that are distributed all across the endocardial surface of the heart
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Can purkinje cells contract?
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YES--they are myocytes but have poorly developed contractile machinery
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Describe how all cardiac cells have the following properties: Automaticity, excitability, conductivity, contractility, and conductivity
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Think about it
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What cells have a Slow AP?
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SA Node and AV Node
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What are the most important membrane related processes in the heart?
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DIFFUSION VIA CHANNEL PROTEINS, primary active transport, and counter transport
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How is calcium transported in the heart?
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Via the L type and T type transporters
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At the beginning of a fast AP, what causes permeability to K?
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IK1--inwardly rectified K channel causing the membrane potential at baseline to be close to the Nernst potential
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What is the Nernst Potential with regards to membrane electrical signaling?
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Point at which the diffusion potential opposes further movement of the ions in spite of the concentration gradient = no further movement of ions
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What happens when the transmembrane voltage of a cardiac cell is slowly depolarized? Where does this happen? What effect does it have?
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Inactivation of the channels occurs without the initial opening and current flow--as long as this partial depolarization exists, the closed, inactive ion channels cannot recover to resting state and won't transport Na+ ions--this is found in the SA and AV nodes--their membrane voltage is generally less negative than -70 mV at all times and fast sodium channels don't play a part in generation of AP here
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At rest, the membrane of cardiac cells is most permeable to what?
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Potassium--inward rectifier channels conduct potassium out of the cell--the ions are also pulled back in by negative charge inside so the potassium EQ potential is set up at -91mV
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From phase 0 to phase 4, what is the predominate ion that is moving?
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Phase 0: Na+ Phase 1: K+ outward Phase 2: balance of outward K+ and inward Ca++ Phase 3: K+ outward Phase 4: K+ (and slightly Na+) maintains EQ potential at -90 mV
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What is the maximum negative potential of pacemaker cells?
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-60 mV causing the fast sodium channels to remain inactivated
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