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Electrical function (Action potential generation and propagation…
Electrical function
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Pacemaker potential
No fast Na+ channels in pacemaker cells. Have "funny" Na+ channels. Closed during AP and open after ends
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If SA node fails, AV node can take over
Movement of cations
More K+ in cell, so K+ moves out of cell (when channels open)
More Na+ and Ca2+ outside of cell, so move into cell (when channels open)
In resting K+ moves out to keep -ve resting, Na+ and Ca2+ channels closed.
In depolarisation K+ channels closed, Na+ and Ca2+ in as channels open
"fast" Na+ channels become refratory after closing (cannot be reopened)
Therefore no temporal summation, cannot undergo tetany. Always contracts then always relaxes
Atrial cell lower refractory period than ventricle as Ca2+ channels open for less time, K+ channels closed for less. Therefore atria capable of beating faster than ventricles. -> Atrial fibrilation
Electrolyte disturbance
Increased potassium
Slows repolaristation, slows heart rate
Decreased sodim
Slows depolarisation, slows heart rate
Decreased calcium
Slow depolarisation, weakened contractility and slow heart rate
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