heart is a series of pumps that are carefully controlled by a very special electrical
system. This electrical system attempts to regulate the heart rate between 60 and 100
beats per minute. The initial electrical signal originates near the top of the upper
chamber on the right side of the heart. This chamber is called the "right
atrium" and the special tissue that generates the signal is called the
"sino-atrial" or SA node.
The electrical signal
continues in a downward fashion through the "atrio-ventricular" or AV node,
where the signal is slowed slightly by special tissue. The AV node is the
"doorway" or relay station to the bundle of His (pronounced Hiss) and the bundle
branches in the lower chambers of the heart.
After passing through the left and right bundle branches, the
impulse arrives at the Purkinje fibers, where it is transmitted to the muscle cells of the
left and right ventricles. Because of the specialized way in which the impulse is
transmitted, the ventricles contract almost simultaneously.
With normal conduction, the cardiac contractions are very
organized and timed so that the top chambers (the atria) contract before the lower
chambers and the heart rate is maintained between 60 and 100 beats per minute.
1. The SA Node.
2. The AV Node.
3. The Bundle of His.
4. The Bundle Branches.
5. The Purkinje fibers.