Bundle of His
From Free net encyclopedia
The bundle of His is a collection of heart muscle cells specialized for electrical conduction that transmits the electrical impulses from the AV node (located between the atria and the ventricles) to the point of the apex of the fascicular branches. The fascicular branches then lead to the Purkinje fibers which innervate the ventricles, causing the cardiac muscle of the ventricles to contract at a paced interval. These specialized muscle fibres in the heart were named after the Swiss cardiologist Wilhelm His, Jr., who discovered them in 1893.
Cardiac muscle is very specialized, as it is the only type of muscle that has an internal rhythm. When a cell of cardiac muscle is placed next to another, they will beat in unison. The fibers of the Bundle of His allow electrical conduction to occur more easily and quickly than typical cardiac muscle. They are an important part of the electrical conduction system of the heart as they transmit the impulse from the AV node (the ventricular pacemaker) to the rest of the heart. The bundle of His branches into the three bundle branches: the right, left anterior and left posterior bundle branches that run along the interventricular septum. The bundles give rise to thin filaments known as Purkinje fibers. These fibers distribute the impulse to the ventricular muscle. Together, the bundle branches and purkinje network comprise the ventricular conduction system. It takes about 0.03-0.04s for the impulse to travel from the bundle of His to the ventricular muscle.
If the Bundle of His is blocked, it will result in dissociation between the activity of the atria and that of the ventricles, otherwise called a third degree heart block. The other cause of a third degree block would be a block of the right, left anterior, and left posterior bundle branches. A third degree block is very serious medical condition that will most likely require an artificial pacemaker.
| Cardiovascular system - Heart - edit |
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| atria (interatrial septum) | ventricles (interventricular septum) | valves (chordae tendinae, papillary muscle)
right heart: (vena cavae, coronary sinus) → right atrium (fossa ovalis) → tricuspid valve → right ventricle → pulmonic valve left heart: (pulmonary veins) → left atrium → mitral valve → left ventricle → aortic valve pericardium | epicardium | endocardium | myocardium conduction system: cardiac pacemaker | Purkinje fibers | bundle of His | SA node | AV node |