Anatomy
and Function of the Heart's Electrical System
The
heart is, in the simplest terms, a pump made up
of muscle tissue. Like all pumps, the heart requires
a source of energy in order to function. The heart's
pumping action comes from an intrinsic electrical
conduction system.
An electrical
stimulus is generated by the sinus node (also
called the sinoatrial node, or SA node), which
is a small mass of specialized tissue located
in the right atrium (right upper chamber) of the
heart. The sinus node generates an electrical
stimulus periodically (60-100 times per minute
under normal conditions). This electrical stimulus
travels down through the conduction pathways (similar
to the way electricity flows through power lines
from the power plant to your house) and causes
the heart's lower chambers to contract and
pump out blood. The right and left atria (the
two upper chambers of the heart) are stimulated
first and contract a short period of time before
the right and left ventricles (the two lower chambers
of the heart). The electrical impulse travels
from the sinus node to the atrioventricular (AV)
node, where impulses are slowed down for a very
short period, then continues down the conduction
pathway via the bundle of His into the ventricles.
The bundle of His divides into right and left
pathways to provide electrical stimulation to
both ventricles. Normally, as the electrical impulse
moves through the heart, the heart contracts about
60 to 100 times a minute. Each contraction of
the ventricles represents one heartbeat. The atria
contract a fraction of a second before the ventricles
so their blood empties into the ventricles before
the ventricles contract.
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