What is the Difference Between Cardiac Muscle and Purkinje Fibers

The heart is the main organ in the circulatory system. Both cardiac muscle and Purkinje fibers can be identified in the heart. Cardiac muscle is one of the three major muscle types of the body and is found in the heart, while Purkinje fibers are large specialized cardiac muscle fibers found in the heart’s ventricular walls.

The key difference between cardiac muscle and Purkinje fibers is their structure. Purkinje fibers are larger than the cardiac muscle and have fewer myofibrils, lots of glycogen and mitochondria, and no T-tubules.

CONTENTS

1. Overview and Key Difference
2. What is a Cardiac Muscle
3. What are Purkinje Fibers
4. Similarities – Cardiac Muscle and Purkinje Fibers
5. Cardiac Muscle vs Purkinje Fibers in Tabular Form
6. Summary – Cardiac Muscle vs Purkinje Fibers
7. FAQ – Cardiac Muscle and Purkinje Fibers

What is a Cardiac Muscle?

Cardiac muscle, also known as heart muscle or myocardium, is one of the three types of vertebrate muscle tissues. It is an involuntary striated muscle that forms the main tissue of the heart wall. The cardiac muscle forms a thick middle layer between the pericardium and endocardium, and blood is supplied via coronary circulation.

Cardiac muscle is usually made up of individual cardiac muscle cells joined together by intercalated discs. It is encased by collagen fibers and other substances that form the extracellular matrix. The cardiac muscle plays a major role in the blood-pumping mechanism of the heart. Furthermore, diseases of the heart muscle are known as cardiomyopathies. Some of them, such as angina and myocardial infarction, affect the function of the heart.

What are Purkinje Fibers?

Purkinje fibers are present in the inner ventricular walls of the heart, just beneath the endocardium, in a space called the subendocardium. They are specialized conducting fibers composed of electrically excitable cells. Purkinje fibers are larger than cardiomyocytes and have fewer myofibrils but many mitochondria.

The Purkinje fibers allow the conduction system of the heart to create synchronized contractions of its ventricles, which are essential for maintaining a consistent heart rhythm. Changes in the function of the Purkinje fibers can lead to diseases such as Purkinje fiber dysplasia.

Similarities Between Cardiac Muscle and Purkinje Fibers

1. Both cardiac muscle and Purkinje fibers can be identified in the heart.
2. They contribute to the proper blood circulation in the body.
3. The changes in both tissues can cause diseases.

Difference Between Cardiac Muscle and Purkinje Fibers

Definition

1. Cardiac muscle is one of the three types of vertebrate muscle tissues exclusively found in the heart.
2. Purkinje fibers are specialized conductive fibers located in the inner ventricular walls of the heart, situated just beneath the endocardium within a space known as the subendocardium.

Size

1. Cardiac muscle fibers are smaller.
2. Purkinje fibers are larger.

Structural Features

1. Cardiac muscle fibers have multiple myofibrils and fewer mitochondria.
2. Purkinje fibers have fewer myofibrils but many mitochondria.

Function

1. Cardiac muscle facilitates blood pumping throughout the cardiovascular system.
2. Purkinje fibers allow the conduction system of the heart to create synchronized contractions of its ventricles, which are essential for maintaining a consistent heart rhythm.

Diseases Associated

1. Diseases associated with cardiac muscle include angina and myocardial infarction, which affect the function of the heart.
2. Purkinje fiber dysplasia is a disease associated with Purkinje fibers.

The infographic below presents the differences between cardiac muscle and purkinje fibers in tabular form for side-by-side comparison.

Summary – Cardiac Muscle vs Purkinje Fibers

The heart is the main organ in the circulatory system. Both cardiac muscle and Purkinje fibers can be identified in the heart. Both are made up of individual cells. Cardiac muscle is one of three types of vertebrate muscle tissues while Purkinje fibers are specialized conductive fibers present in the inner ventricular walls of the heart, just beneath the endocardium, in a space called subendocardium. Thus, this is the summary of the difference between cardiac muscle and purkinje fibers.

FAQ: Cardiac Muscle and Purkinje Fibers

1. What are the two types of cardiac muscle cells?

• There are two major types of cardiac muscle fibers: myocardial contractile cells and myocardial conducting cells. The myocardial conducting cells are also known as pacemaker cells.

2. What are the three functions of the cardiac muscle?

• The primary function of the cardiac muscle is to regulate and maintain the functioning of the heart through the relaxation and contraction of the heart muscles. Other functions include serving as involuntary muscle and participating in movement or locomotion.

3. What is the arrangement of cardiac muscle fibers?

• Cardiac fibers do not assemble in parallel arrays. They bifurcate and recombine to form a complex three-dimensional network. Cardiomyocytes are joined at each end to adjacent myocytes at the intercalated disc, a specialized area of interdigitating cell membrane.

4. What is the function of the Purkinje fibers?

• The main function of Purkinje fibers is to allow the heart’s conduction system to create synchronized contractions of its ventricles. They are also essential for maintaining a consistent heart rhythm.

5. Where are Purkinje Fibers found?

• Purkinje fibers are structures present in the inner walls of the right and left ventricles of the heart, beneath the endocardium, within a space called the subendocardium.

Reference:

1. “Cardiac Muscle.” Encyclopædia Britannica, Encyclopædia Britannica, inc.
2. Paxton, Steve, et al. “Purkinje fibres.” The Histology Guide.

Image Courtesy:

1. “Cardiac Muscles.” By BruceBlaus – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Purkinje fibers” By I, Nathanael (CC BY-SA 3.0) via Commons Wikimedia