What is the Difference Between Purkinje Fibres and Bundle of His

The main difference between Purkinje fibres and bundle of His is that Purkinje fibers occur in the inner ventricular walls of the heart, whereas bundle of His connects the atrial and ventricular chambers of the heart. 

Purkinje fibers and the bundle of His are two specialized muscle bundles of the heart. They are responsible for the contractions of the heart muscle, known as autorhythmic cells.

Key Areas Covered

1. What are Purkinje Fibres
     – Definition, Structure, Function
2. What is the Bundle of His
     – Definition, Structure, Function
3. Similarities Between Purkinje Fibres and Bundle of His
     – Outline of Common Features
4. Difference Between Purkinje Fibres and Bundle of His
     – Comparison of Key Differences

Key Terms 

Bundle of His, Purkinje Fibres

What are Purkinje Fibres

Purkinje fibers are a specialized type of cardiomyocytes that transmit electric impulses to the heart. They are present in the inner ventricular walls of the heart. Generally, these cells are larger than cardiomyocytes. They contain fewer myofibrils but a lot of mitochondria. The main function of Purkinje fibers is to conduct action potentials quickly and efficiently through the ventricles of the heart. Therefore, they contain a higher concentration of voltage-gated sodium channels. Moreover, a lot of glycogen allows Purkinje fibers to appear in a light color.

Figure 1: Purkinje Fibers

Furthermore, the autonomic nervous system is responsible for governing the heart rate. The electrical discharge of the SA node is responsible for the activation of the AV node. The electrical impulses from the AV node come through the bundle of His to the right and left bundles to Purkinje fibers. 

What is the Bundle of His 

The bundle of His is another specialized cell type that connects the AV node to the left and right bundles of the heart. Electrical impulses transmit from the SA node to the AV node of the heart. The bundle of His receives electrical impulses from the AV node. It also transmits impulses to the left and right ventricles.

Figure 2: Bundle of His

Moreover, the bundle of His contains Purkinje-type cells. They contain randomly oriented myofibrils, a lot of mitochondria, and Golgi apparatus. The cells of the bundle of His contain two septate nuclei. The main function of the bundle of His is to connect the left and right bundle branches to the AV node. 

Similarities Between Purkinje Fibres and Bundle of His

• Purkinje fibers and the bundle of His are two specialized cardiac muscle cells.
• They are responsible for the contraction of heart muscles.  

Difference Between Purkinje Fibres and Bundle of His

Definition

Purkinje fibers refer to specialized conducting fibers composed of electrically excitable cells. In contrast, a bundle of His refers to an elongated segment connecting the AV Node and the septal crest’s left and right bundle branches.

Occurrence

While Purkinje fibers occur in the inner ventricular walls of the heart, the bundle of His connects the atrial and ventricular chambers of the heart. 

Structure

Purkinje fibers are larger than cardiac muscle cells but have fewer myofibrils, lots of glycogen and mitochondria, and no T-tubules, while the bundle of His predominantly consist of Purkinje-type cells, slender transitional cells, broad transitional cells, and varying amounts of pacemaker cells. 

Function

Purkinje fibers are responsible for receiving conducting signals originating at the AV node, activating left and right ventricles, while the bundle of His transmits impulses from the AV node to the ventricles.

Conclusion

In brief, Purkinje fibers and the bundle of His are two specialized cardiomyocytes responsible for the muscular contraction of the heart. Purkinje fibers occur in the inner ventricular walls of the heart. They are large cardiac muscle cells with fewer myofibrils and lots of glycogen and mitochondria. They receive conducting signals from the AV node and transmit signals to the left and right ventricles of the heart. In comparison, the bundle of His connects the atrial and ventricular chambers of the heart. It predominantly contains cells similar to Purkinje fibers. Moreover, it transmits impulses from the AV node to the ventricles. Therefore, the main difference between Purkinje fibers and the bundle of His is their structure and function.

References:

1. Wikimedia Foundation. Purkinje fibers. Wikipedia. 
2. Patra C, Zhang X, Brady MF. Physiology, Bundle of His. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan.

Image Courtesy:

1. “Endocardium and subendocardium histology” By Alessandro Scalese – Own work (CC-BY SA 4.0) via Commons Wikimedia
2. “ConductionsystemoftheheartwithouttheHeart-en” By Madhero88 – Own Work (CC-BY SA 3.0) via Commons Wikimedia