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    I'm revising for my AQA AS exams and in the Cardiac cycle topic (diastole, systole) do you need to know all about the Bundle of His; SAN and AVN? My teacher went through it all with us but it's not in any of my text books, and the only paper I've seen it on is one from 2010. I'm doing the new specification by the way.
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    (Original post by rdrowley)
    I'm revising for my AQA AS exams and in the Cardiac cycle topic (diastole, systole) do you need to know all about the Bundle of His; SAN and AVN? My teacher went through it all with us but it's not in any of my text books, and the only paper I've seen it on is one from 2010. I'm doing the new specification by the way.
    Yes; the SAN, AVN and Bundle of His are vital to ensure simultaneous contraction of the heart is maintained. Even though you're doing the new specification, the question has been on many past papers. (Not sure how you've only seen it on 1 - I've seen it on many 5 markers)
    How it works;
    1 - the heart is myogenic, meaning it generates its own electrical impulse
    2 - electrical impulse is initiated by SAN in right atrium
    3 - impulse travels through both atria walls, causing simultaneous contraction of the atria
    4 - impulse travels to the AVN which delays the impulse so that the atria have time to finish releasing their contents into the ventricles
    5 - impulse travels down bundle of his, located in the septum of the heart
    6 - impulse travels to base of the heart, stimulating purkynje fibres
    7 - heart contracts from apex upwards (prevents pooling of blood)

    That's all you need to know at AS level



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