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39 Cards in this Set
- Front
- Back
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What cells activate cardiac muscle cells to sponatneously depolarize?
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Pacemaker cells
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What feature connects cardiac muscle fibers
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Gap junctions
conduct ions |
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Once one cardiac cell is excited, the impulse can sprad to allother cells.
"all-or-none" |
Functional syncytium
Cannot adjust force by temporal/spatial summation |
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Excitation contraction coupling in skeletal...
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Independent of extracellular calcium ions
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What role does extracellular calcium ions play in cardiac cells?
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Extracellular calcium ions are cruical for contraction
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Where is the nuclei in cardiac muscle?
Skeletal muscle? |
Cardiac: centrally located
Skeletal: subssarcolemmal (under PM) |
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How many nuclei per cell does cardiac muscle have?
Skeletal |
Cardiac: one nucleus/cell
Skeletal: multiple nuclei/cell |
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List order of cardiac fibers in order of increasing size
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Atrial<ventricular<purkinje fibers
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List order of cardiac fibers in order of increasing length.
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Atrial<ventricular<purkinje
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Compare the striations of the cardiac fiber types
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Atrial & ventricular: prominent
Purkinje: faint bc lack of contractile protein |
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Do cardiac cells have glycogen?
Which fibers have the most? How does glycogen stain in H&E? |
Yes
Purkinje have most Stains lighter around nucleus |
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What makes-up the largest volume of organelles?
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Myofibrils 50%
Mitochondira 33% |
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Where are the T-tubules located in cardiac m?
in skeletal m? |
Along the Z line
Intersection of I and A bands |
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DiadsA
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Formed by the SR cisternae & T-tubules
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Atrial granules contain?
How is hormone released? |
Secretory granules that contain
ANP. Stretch releases ANP |
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-"spot welds"
-where PM of two cells come very close together |
Macula aderenes (desmosomes)
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-Where actin cytoskeleton comes out and joins intercalated disc
-Allows pulling on PM at a given region to transmit forces to next cell |
Fascia adherens
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How is the cardiac excitation-contraction coupling different from skeletal?
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1. Ca crosses T-tubules through VOLTAGE-gated Ca channels (DHPR)
In skeletal, AP down T-tubule causes conformational change in DHRP which causes conformational change in ryanodine receptors...MECHANICAL change. 2. Activator Ca causes release of Ca from the SR via Ca releases channels (aka ryanodine receptors In skeletal, Ca doesn't bind the receptor since it's a mechanical change. |
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How is Ca pump different in cardiac?
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Calcium pumped out of the cells by Ca pump & Na/Ca exchanger.
Cardiac cells are MORE sensitive to Ca than skeletal muscle |
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the ability to develop contractile force at a specific muscle length
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contractility
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Length-Tension relationship
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-Passive properties of cardiac cause stiffness near plateau that limits inc. in length. So it gets hard to stretch more.
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Cardiac m operates on what two regions of the length-tension curve?
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Operates on the ascending & plateau region
No one ever sees descending curve |
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Ascending region of the length-tension relationship
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Stretch-->inc. Calcium-->more crossbridging
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Descending region of the length-tension relationship
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Due to decreased overlap of the myosin heads & actin sites.
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When contractility is increased by elevating cAMP what happens?
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1. Inc. contraction force
2. Inc. velocity of shortening at a load 3. Inc. speed of BOTH contraction & relaxation |
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How does NE inc. contractility?
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NE-->B-adrenergic receptor-->Gs-->adenylate cyclase-->inc. protein kinase A
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What proteins does Protein Kinase A phosphorylate?
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1. Dihydropiridine receptor
2. Phospholamban |
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Dihydropiridine Receptor
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Phosphorylated-->inc. in activator Ca-->binds to ryanodine receptor-->release of Ca from SR-->inc. cytosolic Ca-->inc. contractile force
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Phospholamban
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Protein associated with the Ca pump in the membrane of the SR
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What happens when Phospholamban is phosphorylated?
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Inc. pumping of Ca into SR
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What are 2 benefits of Phospholaman?
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1. Way to store more Ca
2. Sweeps Ca out of sytosol and into SR more quickly after excitation-->quick relaxation |
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Do nerves initatiate contraction in cardiac m?
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No, but do adjust both heart rate & contractility
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What is the role of sympathetic & parasympathetic nerves for cardiac m?
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Sympathetic-->release NE-->inc. contracility
Parasympathetic-->release Ach-->dec. contractility |
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Why does force of contractility inc. when the heart rate inc (frequency of contraction)?
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When freq inc., some Ca that should go into SR is left behind.
Temporary Ca build-up-->more actin-myosin interactions |
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Digitalis
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ability to inhibit the Na/K pump
results in: 1. Inc. in intracellular [Na] 2. Slows down the Na/Ca exchanger 3. Inc. cytosolic Ca-->inc. crossbridges |
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How does digitalis slow down the Na/Ca exchanger?
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-Na/Ca exchanger imports 3 Na in and 2 Ca out.
-If administer digitalis-->build-up of intracellular Na -Less Na pumped in, less Ca pumped out -MORE cytosolic Ca! |
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Decrease in contractility are caused by?
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1. Dec. in cytosolic [Ca]
2. Dec. supply of ATP |
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+ inotropic agents caused?
- inotropic agents...? |
Increase contractility
Decrease contractility |
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What are the effects of long term overstimulation of NE?
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excess NE-->stimulation of MAP Kinase pathway-->cell division-->hypertrophy & apoptosis-->dec. in amount of cells-->heart failure
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