Bundle of His: Definition, Function & Anatomy

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  • 0:04 The Bundle of His
  • 0:53 Pacemaker vs Myocardial
  • 2:37 The Bundle of His Function
  • 4:21 Lesson Summary
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Lesson Transcript
Instructor: Caroline Rivera

Caroline has been teaching college biology for nearly 15 years. She has earned master's degrees in Anthropology & Biology (79 gsh) and a PhD in Community College Leadership.

The average person's heart beats 60-100 times per minute, pumping out an impressive 5 liters of blood. Sound simple? Well, the heart's function is anything but simple. The following lesson provides an overview of the intrinsic conduction of the heart with a special focus on the bundle of His.

The Bundle of His

Feel that thump, thump, thumping in your chest? The heart is a complex organ that is controlled and regulated by the autonomic nervous system. We often take for granted 'that our heart will go on and on', but what are the underlying forces at play that regulate the rate and force at which the heart beats? It's the work of the intrinsic conduction system . Housed in the atria are the sinoatrial node, the internodal pathways, and the atrioventricular node. Bundle branches and Purkinje fibers are found in the ventricles. In between the atria and ventricles is the bundle of His. Together, they set the pace of the heart's contractions. The intrinsic conduction system begins at the sinoatrial node, travels through the internodal pathways, then to the atrioventricular node, bundle of His, bundle branches, and finally the Purkinje fibers.

Pacemaker vs Myocardial

The contraction of the heart is facilitated by the hard work of two types of cells operating together to keep the body supplied with blood.

The first are pacemaker cells, which are made up of specialized heart muscles that are self-excitatory and controlled by the autonomic nervous system (such as heart rate increases during a fight-or-flight response). You can think of these cells as the bosses because they set the pace of the heart's contractions.

At rest, pacemaker cells have an electrical charge of -60 millivolts (mV). The heart's pacemaker cells begin in an area located at the convergence of the opening of the superior vena cava in the right atrium called the S-A node. These specialized cardiac muscle fibers travel from the S-A node to the A-V node via three internodal pathways. As the electrical impulse enters the A-V node, there is a delay of 0.09s which allows time for the atria to empty into the ventricles.

From the A-V node, the impulse enters the penetrating portion of the bundle of His where there is another brief delay of 0.04s as it enters the fibrous tissue separating the atria and ventricles before the impulse passes into the ventricles.

The second are myocardial cells, the cardiac muscle cells themselves. They can be considered worker cells because they respond to the impulses of the bosses, the pacemaker cells. At rest, the myocardial cells have an electrical potential of -90mV. These cells' electrical charges vary based on the concentration of ions (for example sodium, calcium, potassium) inside and outside the cells. The impulses propagated at the sinoatrial node travel through the rest of the intrinsic conduction system and synapse with myocardial cells to trigger the heart's contraction.

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