circulatory system notes, Lecture notes of Anatomy

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Each beat begins in the right atrium – with an action potential signal from the signal atrial or sa node

The signal spreads across both atria causing the muscle cells to depolarise and contract, inducing a phase known as atrial systole = p wave

Period of conduction that follows atrial systole and proceeds the contraction of the ventricle is known as the pr segment

And spreads through the bundle branches

And the large dimeter purkinje fibres along the ventricle walls

As the signal spreads through the ventricle, the contractile fibres depolarise and contract very rapidly, inducing ventricular systole, known as the QRS complex represents this rapid ventricular depolarisation. atrial repolarisation also occurs at this time, but any atrial activity is hidden on the ECG by the QRS complex

As the signal passes out of the ventricles, the ventricular wall starts to relax and recover, a state known as ventricular diastole

The Q-T interval represents the time it takes for both depolarisation and repolarisation of the ventricles to occur

This repeats with every heart beat

ECG is not a tracing of a single action potential, is an amalgamation of the many action potentials that constitute the electrical activity of the heart