Cardiac Electrophysiology Lecture Powerpoint Flashcards
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How does the wave of electrical current generated in the heart spread to adjoining cells?
gap junctions allow ions to pass freely from cell to cell
During depolarziation of the cardiac cells ___ occurs in the cardiac myocytes, during repolarization ___ occurs
Contraction, relaxation
In cell, for depolarization of resting membrane potential must become less ____
negative
At resting state, what ion is found in higher conc inside the cardiac muscle cell?
K+
Where are the 3 normal areas of the heart to have automaticity?
- SA node
- AV nde
- Bundle of His/purkinje fibers
The pacemaker cell with the ___ rate will over ride the others
highest
At rest, Na+ conc. is higher ___ the cell. K+ conc. is higher ___ cell, Ca2+ is at higher conc. ___ cell
outside, inside, outside
Threshold value to initiate an AP in a pacemaker cell
-40 mV
Cardiac muscle AP is much ____ than skeletal muscle because of a longer ____
Slower, refractory period
Skeletal vs cardiac muscle differences (4)
- intrinsic impulse generation in cardiac
- plateau phase in cardiac
- longer refractory period in cardiac
- summation not possible in cardiac
There are NO _____ channels operating in the SA node, but they are present in the cardiac muscle
fast Na+
Action potential generation in autorhythmic cell mech of action
- autorhythmic cells begin depolarizing (becomes less negative) due to slow continuous inward movement of Na+ and reduced outward movement of K+ from -60mV approx resting potential
- upon reaching threshold -40mV, Ca2+ channels open and Ca2+ rushes into cell making cell much less negative, depolarization occurs
- K+ channels are triggered at -10mV and opened and Ca2+ channels close resulting in K+ flow out of the cell (repolarization)
- Ion pumps use ATP to move Ca2+ back to extracellular space and Na/K ATPase pumps Na+ out of cell and K+ back into cell
Action potential generation in cardiac myocyte mech of action
- -90mv is resting potential for the cardiac myocyte
- Positive ions moving thru gap junctions create small voltage change initiating depolarization
- this stimulates opening of fast Na+ cells at -70mV, begins depolarization
- myocyte contraction begins here
- Depolarization to +20mV triggers opening of slow Ca2+ channels, allowing Ca2+ entry from extracellular space
- At same time, depolarization to +20mV triggers K+ channels to allow K+ to begin leaving the cell
- This generates the plateau phase
- Ca2+ channels close and more K+ channels open causing cell to become less positive (repolarization)
- myocyte relaxation begins here
- simultaneously, ions pump Ca2+ out to extracellular space and Na+/K+ATPase pumps Na+ out and K+ back in
Effective/Absolute refractory period
Protective mech by limiting frequency of APs preventing tetany, period where 2nd AP cannot be initiated occurring during the majority of the AP cycle
Relative refractory period
Period following the effective/absolute refractory period where a 2nd AP is inhibited but not impossible, requiring supra threshold stimulation to elicit AP, they tend to be slower and wider since not all Na+ channels have had time to recover
Primary pacemaker of heart normally and where is it located anatomically?
SA node, posterior wall of right atrium
Intrinsic rate of the heart of the SA node
100-110 BPM