The Primary Pacemaker the Sinoatrial Node
The sinoatrial node also known as the SA
node is a group of cells positioned on the wall of the
right atrium, near the entrance of the superior vena cava. These
cells are modified cardiac myocytes. They possess some contractile
filaments, though they do not contract.
Cells in the SA node will naturally discharge
at about 70-80 times per minute.
Because the sinoatrial node is responsible for
the rest of the heart's electrical activity, it is sometimes called
the primary pacemaker, the natural pacemaker.
If the SA node doesn't function, or the impulse
generated in the SA node is blocked before it travels down the electrical
conduction system, a group of cells further down the heart will
become the heart's pacemaker.
The secondary pacemker control the AV node
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Heart
