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36 Cards in this Set

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