How is the cardiac cycle controlled?

AS Biology Unit 1 revision

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The sinoatrial node (SAN) produces a wave of electrical activity which causes both atria to contract, followed by the ventricles. The SAN initiates the heartbeat.

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A wave of electrical activity spreads out from the SAN across both atria, causing them to contract.

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A layer of non-conductive tissue (the atrioventricular septum)  prevents the wave crossing the ventricles.

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The wave of electrical activity is allowed to pass through a second group of cells called the atrioventricular node (AVN), which lies between the atria.

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The AVN,after a short delay, conveys a wave of electrical activity between the ventricles along a series of specialised muscle fibres called the bundle of His.

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The bundle of His conducts the wave through the AV septum to the base of the ventricles,where the bundle branches into smaller fibres.

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The wave of electrical activity is released from these fibres, causing the ventricles to contract quickly at the same time, from the apex of the heart upwards.

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