Page 86 - The Miracle of Electricity in the Body

84 THE MIRACLE OF ELECTRICITY IN THE BODY

never tiring. Furthermore, they must know the level of electrical current
that will cause the heart to work as a whole, and to produce that current
at exactly the right level—neither more nor less.

When spread out thinly on a microscope slide, different heart cells
will beat at different speeds. But when combined together, they form a
single tissue that behaves as a single entity. The same applies to the heart
cells in the human chest; although each one initiates its own beat, they
all beat in a rhythmic harmony. The pacemaker in your heart contains an
internal clock that regulates the speed at which your heart beats. This
pacemaker is actually a collection of cells, but it functions far more per-
fectly that any electronic device. Using conductive fibers, it distributes
the electrical current it produces to every point in the heart muscle. But
this electricity proceeds at different but controlled speeds. When both
heartbeat and transmission system are working properly, they carry out
an ordered and determined distribution of electricity.
The heart possesses a natural battery that regulates the speed at
which it beats—a specialized electrical cell node known as the SA node,
(for sinus or sinoatrial node), located in the upper part of the right atri-
um. These cells initiate electrical impulses that stimulate the heart mus-
cles to contract regularly. The SA node produces the electrical stimuli
that spread throughout the heart, ensuring that its four chambers all
contract at the proper times. This electrical impulse travels from one side
of the heart to the other so rapidly that it gives the impression all the
cells are beating at once. This rhythm is the heart’s normal beat, which is
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between 60 and 100 times a minute. It takes 0.3 of a second for the elec-
trical impulse to move from the SA node to the region known as the AV
node located between the atria and ventricles, and this is known as the
normal sinus rhythm. The AV node is the location of the cells that pro-
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duce the second electrical current that completes the heartbeat.
Just like a sparkplug in an engine, the heart cells fire many times a
minute. Each firing passes through a specialized electrical path and
stimulates the muscle walls of the heart’s four chambers in a specific or-
der. First the upper two chambers of the atria are stimulated, after which