Repolarization
1. Additional voltage gated K+ channels open 2. Outflow of K+ restores the negative resting membrane potential (-90mV) 3. Concurrently, Ca++ channels are closing contributing to repolarization
The actual mechanism of contraction for cardiac muscle is similar to skeletal muscle.
Refractory Period: a 2 nd contraction cannot be triggered during contraction. This allows for relaxation to occur and for the heart to refill with blood.
Electrocardiogram
As APs propagate through the heart, electrical currents are generated and can be detected on the surface of the body. An Electrocardiogram (ECG) records these signals.
An ECG may determine:
If the conducting pathway is abnormal If the heart is enlarged If certain regions of the heart are damaged
In a typical record, 3 recognizable waves appear with each heartbeat.
1) P Wave : represents atrial depolarization which spreads from the SA node through contractile fibres in both atria.
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