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Electricity and the Heart
11
Cardiac cells can lose their internal negativity in a process called
depolarization
.
Depolarization is the fundamental electrical event
of the heart
. In some cells, known as pacemaker cells, it occurs
spontaneously. In others, it is initiated by the arrival of an
electrical impulse that causes positively charged ions to cross the
cell membrane.
Depolarization is propagated from cell to cell, producing a wave
of depolarization that can be transmitted across the entire heart. This
wave of depolarization represents a flow of electricity, an electrical
current, that can be detected by electrodes placed on the surface of
the body.
After depolarization is complete, the cardiac cells restore their
resting polarity through a process called
repolarization
. Repolarization
is accomplished by the membrane pumps, which reverse the flow of
ions. This process can also be detected by recording electrodes.
All of the different waves that we see on an EKG are manifestations
of these two processes: depolarization and repolarization.
Sometimes lethal disturbances in the conduction of electricity
through the heart occur because of an inherited disorder of
these transmembrane ion channels. Fortunately, these so-called
channelopathies
are quite rare. Many different genetic mutations
affecting the cardiac ion channels have been identified, and more
are being discovered every year.