Control of The Cardiac Cycle

  • Created by: Saarah17
  • Created on: 08-11-22 19:28

Control of The Cardiac Cycle

—> the heart is myogenic : the muscles can contract on its own.

—> it needs coordinating to ensure it contracts in a rhythm.

—> this is the job of the Sino-Atrial Node (SAN), Atrio-Ventricular Node (AVN), Bundle of His and Purkinje fibres.

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1. Sino-Atrial Node

—> found in the wall of the right atrium.

—> peacemaker : initiates the heartbeat and sets the heart rate at 70-80 beats-min but this can be altered during activity or rest.

—> generates an electrical impulse that propagates across both atria walls causing them to contract at the same time.

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2. Atrio-Ventricular Node

—> electrical impulse from SAN is picked up by the AVN in the septum.
—> this is a gateway for electrical impulses to pass to the ventricles.

—> AVN imposes a slight delay in sending the wave of excitation to the ventricles
—> allowing the atria to finish contracting and to fully empty is blood before the ventricles contract
—> meaning they don’t contract at the same time as the atria.

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3. Bundle of His and Purkinje Fibres

—> Bundle of His are specialised in muscle fibres
—> consists of the right and left bundle branches.
—> conduct electrical impulse down the interventricular septum down to the apex.

—> the Purkinje fibres the spread up the ventricle walls transmitting the electrical impulse
—> causes contraction of the ventricles from the apex upwards.
—> pushes the blood up and out of the heart which means that the ventricles can completely empty.

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Cardiac Cycle : Control of Cardiac Cycle

Atrial Systole :

  • atria contract, ventricles relax
  • atria volume decreases, pressure increases
  • blood is pushed through the AV valves down into ventricles


  • SAN initiates heartbeat and spreads impulse across atria wall causing them to contract.
  • impulse doesn’t spread to ventricles by picked up by AVN which imposes a delay.
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Ventricular Systole

  • ventricles contract, atria relax
  • ventricle volume decreases, pressure increases higher than atrial pressure
  • blood pushes the AV valves shut and opens the SL valves


  • Bindle of His picks up the impulse from AVN and spreads down septum to the apex.
  • Purkinje fingers branch and spreads up the ventricle wall to cause contractions of ventricles from the apex upwards.
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  • whole heart relaxes
  • SL valves shut as ventricular pressure starts to drop
  • atria begins to fill with blood which increases the pressure pushing the AV valves open
  • blood trickles down into the ventricles


  • electrical activity of the heart recovers so nothing contracts
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