What is the Difference Between Cardiomyocytes and Pacemaker Cells

The main difference between cardiomyocytes and pacemaker cells is that cardiomyocytes are the cells in the cardiac muscle, whereas pacemaker cells are specialized cardiac muscle cells capable of generating spontaneous action potentials responsible for the contraction of the heart. 

Cardiomyocytes and pacemaker cells are two cell types that occur in the heart. They generate action potentials responsible for the heartbeat. 

Key Areas Covered

1. What are Cardiomyocytes
– Definition, Structure, Function
2. What are Pacemaker Cells
– Definition, Structure, Function
3. Similarities Between Cardiomyocytes and Pacemaker Cells
– Outline of Common Features
4. Difference Between Cardiomyocytes and Pacemaker Cells
– Comparison of Key Differences

Key Terms 

Cardiomyocytes, Pacemaker Cells

What are Cardiomyocytes

Cardiomyocytes, or cardiac muscle cells, are the muscular tissue that occurs in the heart. They are Y-shaped cells that are shorter and wider than skeletal muscles. Each cardiac muscle cell is mononucleated. Since it is high energy requiring muscle, the cardiac muscle cells comprise many mitochondria and myoglobin. The arrangement of actin and myosin striates the cardiac muscle cells. Thickly arranged myosin filaments form dark bands on the cardiac muscle cell, striating it. The light color bands occur due to the loosely arranged actin filaments.

Figure 1: Cardiac Muscle 

Furthermore, each cardiac muscle cell is in contact with another three or four cardiac muscle cells. The overlapping region in each cell forms finger-like extensions in the cell membrane called intercalated disks. The structure of the intercalated disk forms gap junctions and desmosomes between the two cells, allowing the passage of electrochemical signals between the two cells. They are responsible for pumping blood throughout the body of animals via highly coordinated, rhythmic muscular contractions.

What are Pacemaker Cells

Pacemaker cells are the cells that create action potentials responsible for the contraction of cardiac muscle. Cardiac muscle is capable of contracting very quickly in a wave-like pattern. The pacemaker cells that occur within the cardiac muscle allow the muscle to contract in its rhythm in a process known as autorhythmicity. Thus, the pacemaker cells serve as a functional unit in stimulating cardiac muscle, and the pacemaker cells are referred to as syncytium. The pacemaker cells also receive neuron signals from the autonomic nervous system to increase or decrease the heart rate. The action potential of the cardiac muscle cells is relatively long.

Figure 2: Cardiac Pacemaker

Moreover, the cardiac muscles have a sustained depolarization known as a ‘plateau.’ The plateau contains channel proteins’ entry of calcium ions into the cardiac muscle cells. The sustained depolarization provides a longer contraction to the cardiac muscle.

Similarities Between Cardiomyocytes and Pacemaker Cells

• Cardiomyocytes and pacemaker cells are two cell types that occur in the heart.
• They are responsible for the contraction of heart muscles. 

Difference Between Cardiomyocytes and Pacemaker Cells

Definition

Cardiomyocytes refer to the contractile myocytes of the cardiac muscle, while pacemaker cells refer to highly specialized myocardial cells with an intrinsic ability to depolarize rhythmically and initiate an action potential.

Significance

Cardiomyocytes are the cells in the cardiac muscle, while pacemaker cells are specialized cardiac muscle cells capable of generating spontaneous action potentials responsible for heart contraction.

Structure

Cardiomyocytes are Y-shaped, mononuclear cells, while the highest concentration of the pacemaker cells occurs in the SA node. 

Function

Pumping blood throughout the body is the primary function of the cardiomyocytes, while the generation of the action potentials is the primary function of the pacemaker cells.  

Conclusion

In brief, cardiomyocytes and pacemaker cells are two cell types that occur in the heart. Cardiomyocytes make up the heart. They are Y-shaped cells. Their primary function is to pump blood throughout the body. In comparison, pacemaker cells are specialized cardiomyocytes that generate action potentials responsible for heart muscle contraction. They concentrate on the SA node. Therefore, the main difference between cardiomyocytes and pacemaker cells is their structure and function. 

References:

1. Saxton A, Tariq MA, Bordoni B. Anatomy, Thorax, Cardiac Muscle. [Updated 2022 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-

Image Courtesy:

1. “Glanzstreifen” By Dr. S. Girod, Anton Becker – Own work (CC-BY 2.5) via Commons Wikimedia
2. “ConductionsystemoftheheartwithouttheHeart-en” By Madhero88 – Own Work (CC-BY SA 3.0) via Commons Wikimedia