The Heart Continued...

• Human heartbeats originate from the SA node near the right atrium.

• Cardiac muscle cells contract, sending a signal to other muscle cells in the heart to contract.

• The signal spreads to trigger the AV node • Signals carried from the AV node, then

spread and cause the ventricles to contract simultaneously.

Electrical Conduction

Electrical Conduction

Measurement of Heart Contractions

• An electrocardiogram (ECG) measures changes in electrical potential across the heart– detects the contraction pulses that pass over the

surface of the heart. – ECGs are useful in diagnosing heart

abnormalities.

Electrical conduction across the heart

• The P wave represents the contraction impulse of the atria, the T wave the ventricular contraction.

Abnormalities