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36 Cards in this Set
- Front
- Back
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What triggers cardiac contraction?
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An electrical action potential.
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T or F:
The atria and ventricles contract together in a normally functioning heart. |
False - atria contract 50 to 150ms before the ventricles.
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What word describes the electrical linking of numerous cardiac cells allowing them to contract together?
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Syncytium
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What structure allows cardiac cells to be electrically linked?
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Intercalated discs (gap junctions)
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What term is given to cardiac cells that spontaneously depolarize?
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Pacemaker cells
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Where in a normal heart do you find cells that depolarize to threshold the quickest?
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The Sino-Atrial (SA) node
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T or F:
Motor neurons are necessary to initiate cardiac contractions. |
False - not every cardiac cell is innervated.
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What are the components of the conduction system of the heart?
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SA node
Internodal pathways AV node AV bundle (bundle of His) Left/Right Bundle Branches Purkinje Fibers |
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How does an AP propegate from the SA node to the AV node? How long does this take?
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Via internodal pathways.
0.03 sec |
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What delays ventricular contraction? How long is this delay?
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AV node slows AP conduction. Adds ~0.1 sec delay.
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What structure(s) allow for the nearly synchronous contraction of both ventricles?
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Rapid conduction through R and L bundle branches and Purkinje Fibers.
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Is a cardiac AP long or short?
How long/short relative to a skeletal muscle AP? |
Very long.
~2 orders of magnitude longer (100 to 250ms vs 1-2 ms) |
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What specifically allows for this long cardiac AP?
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Slow calcium channels
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What describes the release of Ca from the SR of a cardiac cell?
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Ca induced Ca release
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What membrane-bound structures play a role in stopping a cardiac contraction?
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Ca ATP pump > 1 Ca out
Na/Ca exchanger > 1 Ca out/3 Na in Na/K ATP pump > 3Na out and 2K in |
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What does Digitalis act on?
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Na/K pump inhibitor
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What are the relative intra/extracellular concentration differences for Na, K, and Ca? The equilbrium potential?
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Extracellular
Na 145, K 4, Ca 2 Intracellular Na 10, K 135, Ca .0001 Equilibrium Potential Na 70, K -94, Ca 132 |
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Name four contractile differences of Cardiac Muscle vs. Skeletal Muscle.
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1) Spontaneous Depolarization
2) AP spreads cell-to-cell 3) Long AP 4) Slow Ca channels |
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What contracts during Systole? During Diastole?
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Systole - ventricles contract
Diastole - ventricles RELAX and fill w/blood |
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What are the resting chemical and electrostatic potentials of cardiac cells? Are Na channels open or closed here?
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60mV chemical; 90mV electrical
Na channels are closed |
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At what electrostatic potential do Na channels open?
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~ -65 mV
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How many gates does a Na channel have? What are their names and functions?
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2 gates:
m gate - quickly opens at -65 mV allowing Na into cell h gate - slowly begins closing at -65mV, eventually preventing Na influx |
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What causes Na influx past the electrostatic 0 point?
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The high chemical Na concentration gradient
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What happens at phase 0 of an Action potential?
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Membrane depolarization causes Na channels to open
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What coincides with phase 1 of an AP?
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K channels open allowing K to leave cell along its concentration gradient; partially repolarizes cell
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Why is there a plateau during phase 2?
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Net influx of Ca is balanced by net efflux of K (via Ca/K channels)
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Which phase has the highest K permeability? The lowest K permeability?
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Phase 3 is highest; efflux of K exceeds influx of Ca
Phase 2 is lowest; Na/Ca influx influences K permeability |
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How long does a normal plateau phase last?
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(phase 2); 0.1 to 0.2 sec
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What happens during phase three to repolarize the membrane?
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Ca channels close.
Na/K ATPase removes Na Ca influx into SR Ca/Na exchanger removes Ca |
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When is Na permeability the highest? When is Ca permeability the highest?
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Na is highest during phase 0
Ca is highest during phase 2 |
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What term describes the time after one AP during which another AP cannot be initiated?
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Absolute Refractory Period
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What dictates the duration of the refractory period?
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The duration of the AP
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What does the long refractory period guarantee?
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Period of relaxation and refilling between contractions
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T or F
Both Skeletal and Cardiac muscle can experience tetanization. |
False
The 100x shorter AP in skeletal muscle allows for shorter refractory periods; APs can fuse and tetanize. |
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What prevents a tetanic or sustained contraction in cardiac cells?
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The long AP of cardiac muscle.
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The period where cells require a larger than normal stimulus for excitation is called what?
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Relative refractory period
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