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A-Level Biology OCR A

Electrical Excitation Ventricles Sequence Events Wave Bundle Apex

The heartbeat sequence involves the SAN initiating excitation causing atrial contraction, followed by the AVN imposing a delay before stimulating the Bundle of His, which conducts excitation to the ventricular apex. Purkyne fibers then spread this excitation up the ventricle walls, triggering contraction.

The heartbeat sequence involves the SAN initiating excitation causing atrial contraction, followed by the AVN imposing a delay before stimulating the Bundle of His, which conducts excitation to the ventricular apex. Purkyne fibers then spread this excitation up the ventricle walls, triggering contraction.

Front Write sequence of bullet points to describe the sequence of electrical events of the heart beat.
Back Electrical events of the heartbeat:
  • Wave of electrical excitation begins in SAN, causing atria to contract & initiating the heartbeat
  • Non-conducting tissue layer (septum) prevents excitation passing directly to ventricles
  • Electrical activity picked up by AVN which imposes slight delay before stimulating bundle of His 
  • bundle of His splits into two branches and conducts wave of excitation to the apex
  • At apex, Purkyne fibres spread out thru walls of ventricles of both sides and spread excitation triggers contracation of ventricles, starting at apex

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