Control of the cardiac cycle

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Heart muscle (cardiac muscle) can initate its own contraction, because of this it is describe as myogenic The muscle will contract and relax even when it isn't connected to the body.

 The muscles from artria and ventricles also have their own natural frequency of contraction however the atrial muscle tends to contract at a higher frequency than the ventricular muscle.  This property could cause inefficient pumping (known as fibrilliation) if the contractions of the chambers are not synchronised. So there must be a mechanism that is capable of coordinating all 4 chambers.

 So how does this work?

At the top of the right atrium near where the vena cava empties blood into the atrium is the sinoatrial node (SAN). This small patch of tissue generates electrical activity which in a human can take place 55-80 times a minute. The SAN is also known as the pace maker.

This wave of electrical activity travels along the membranes of the muscle tissue which causes the cardiac muscle cells to contract which is known as atrial systole.


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