Cardiac muscle cells

Cardiac Muscle Cells

Cardiac muscle cells, also known as cardiomyocytes, are the muscle cells that make up the cardiac muscle tissue of the heart. These cells are responsible for the contractile function of the heart, enabling it to pump blood throughout the body. Cardiac muscle cells are unique in their structure and function, distinguishing them from other types of muscle cells such as skeletal and smooth muscle cells.

Structure

Cardiac muscle cells are striated, similar to skeletal muscle cells, but they are shorter and branched, forming a complex network. Each cell contains one or two centrally located nuclei. The striations are due to the organized arrangement of actin and myosin filaments within the cells, which are essential for muscle contraction.

Intercalated Discs

A distinctive feature of cardiac muscle cells is the presence of intercalated discs. These are specialized connections between adjacent cardiomyocytes that support synchronized contraction of the heart muscle. Intercalated discs contain three types of cell junctions:

• Desmosomes: These provide mechanical strength by binding cells together.
• Gap junctions: These allow for electrical coupling between cells, enabling the rapid spread of action potentials.
• Fascia adherens: These anchor actin filaments and transmit contractile forces between cells.

Function

The primary function of cardiac muscle cells is to contract and generate force to pump blood. This is achieved through the sliding filament mechanism, where actin and myosin filaments slide past each other, shortening the sarcomere and thus the muscle cell.

Excitation-Contraction Coupling

Cardiac muscle cells are electrically excitable and can generate action potentials. The process of excitation-contraction coupling in cardiomyocytes involves the following steps:

1. Depolarization: An action potential travels along the cell membrane, causing depolarization. 2. Calcium Influx: Voltage-gated calcium channels open, allowing calcium ions to enter the cell. 3. Calcium-Induced Calcium Release: The influx of calcium triggers the release of more calcium from the sarcoplasmic reticulum. 4. Contraction: Calcium binds to troponin, causing a conformational change that allows actin and myosin to interact and contract. 5. Relaxation: Calcium is pumped back into the sarcoplasmic reticulum and out of the cell, leading to muscle relaxation.

Metabolism

Cardiac muscle cells have a high demand for energy and are rich in mitochondria, which produce ATP through oxidative phosphorylation. They primarily use fatty acids and glucose as energy sources, but can also utilize lactate and ketone bodies.

Regeneration

Unlike skeletal muscle cells, cardiac muscle cells have a limited ability to regenerate. Damage to the heart muscle, such as from a myocardial infarction, often results in the formation of scar tissue rather than new muscle tissue. Research is ongoing into ways to enhance the regenerative capacity of the heart.

Clinical Significance

Cardiac muscle cells are central to the function of the heart, and their dysfunction can lead to various cardiovascular diseases. Conditions such as heart failure, arrhythmias, and cardiomyopathy are often related to problems with cardiomyocyte function or structure.

See Also

• Skeletal muscle
• Smooth muscle
• Myocardium
• Heart

References

• Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., & Walter, P. (2002). Molecular Biology of the Cell. Garland Science.
• Bers, D. M. (2002). Cardiac excitation-contraction coupling. Nature, 415(6868), 198-205.