Cardiac muscle definition
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These studies suggest cardiac muscle is a striated muscle with a sarcomere structure, composed of cross-striated fibers forming a three-dimensional network, and is crucial for pumping blood through the body.
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Definition and Characteristics of Cardiac Muscle
Cardiac Muscle Structure and Morphology
Cardiac muscle is a type of striated muscle that shares structural similarities with skeletal muscle, particularly in its sarcomere organization, which gives it a striated appearance under a microscope . The muscle fibers are quasi-cylindrical and form a complex three-dimensional network through bifurcation and interdigitating connections at specialized junctions called intercalated discs. These intercalated discs are crucial for the mechanical and electrical connectivity between cardiac muscle cells, or myocytes, allowing for synchronized contraction.
Functional Properties of Cardiac Muscle
Cardiac muscle cells are highly energetic and contract continuously without fatigue, enabling the heart to pump blood throughout the body efficiently. Each cardiac myocyte coordinates its activity with billions of neighboring cells to maintain a consistent and powerful heartbeat, pumping over 7,000 liters of blood daily. The action potential in cardiac muscle is notably long-lasting, which prevents tetanic contractions and ensures rhythmic beating.
Regulation of Contraction
The contractility of cardiac muscle is influenced by several factors, including heart rate, circulating epinephrine, and sympathetic nerve stimulation, all of which alter the amount of calcium available to the contractile system. Calcium plays a pivotal role in cardiac muscle contraction, entering the cell during the action potential plateau and triggering the release of internal calcium stores from the sarcoplasmic reticulum. This calcium influx is essential for the activation of the contractile machinery within the muscle cells.
Energy Metabolism
Cardiac muscle primarily relies on oxidative metabolism for energy, utilizing lactic acid and free fatty acids as its main fuel sources. Unlike skeletal muscle, cardiac muscle has limited capacity for anaerobic metabolism, making it highly dependent on a continuous supply of oxygen to sustain its activity.
Conclusion
In summary, cardiac muscle is a specialized, striated muscle type that forms the heart and is essential for pumping blood throughout the body. Its unique structural features, such as intercalated discs, and its reliance on calcium for contraction regulation, distinguish it from other muscle types. The continuous, fatigue-resistant contractions of cardiac muscle are powered by oxidative metabolism, highlighting its critical role in maintaining cardiovascular function.
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