Which of the following represents the correct order of the cardiac cycle?
a) purkinje fibers, av nodes, sa node, bundle of his
b) av node, sa node, bundle of his, purkinje fibers
c) sa node, bundle of his, av node, purkinje fibers
d) sa node, av node, purkinje fibers, bundle of his
e) sa node, av node, bundle of his, purkinje

E; SA node, AV node, bundle of His, Purkinje fiber

Explanation:

During each cardiac cycle, the heart contracts and then relaxes.

As deoxygenated blood flow into the left atrium, the SA (Sino-atrial) node triggers a wave of contraction that spreads over the heart muscle of both atria, emptying the atria.

When electrical impulse reaches the AV (Atrioventricula) node it is slowed down to allow the atria to finish emptying into the ventricle. After this, the AV node triggers its own electrical impulse, which quickly spreads to the ventricular muscle through the AV bundle, bundle of His and Purkinje fibre.

This results in a wave of contraction which sweeps upwards from the apex of the heart to the base pumping the blood into the pulmonary artery and the aorta.

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