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Cardiac muscle, also known as myocardium or heart muscle, is one of three major categories of muscles in the human body, alongside smooth muscle and skeletal muscle. It is composed of cardiac muscle cells, or cardiomyocytes, which are striated, branched, and contain many mitochondria. Unlike skeletal muscle, cardiac muscle is under involuntary control, meaning it operates without conscious control to maintain the heartbeat. The primary function of cardiac muscle is to pump blood into circulation by generating sufficient force.
| Characteristics | Values |
|---|---|
| Type | One of three major categories of muscles found in the human body, along with smooth muscle and skeletal muscle |
| Function | To pump blood into circulation by generating sufficient force |
| Contractile Functions | Require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones |
| Cardiac Action Potential | Lasts approximately 200 ms and is divided into 5 phases: resting, upstroke, early repolarization, plateau, and final repolarization |
| Appearance | Striated, meaning it has a banded appearance similar to skeletal muscle |
| Control | Involuntary |
| Composition | Made up of sarcomeres that allow for contractility |
| Contraction | The rise in calcium causes the cell's myofilaments to slide past each other in a process called excitation-contraction coupling |
| Calcium | Electrical stimulation in the form of a cardiac action potential triggers the release of calcium from the cell's internal calcium store, the sarcoplasmic reticulum |
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What You'll Learn
Cardiac muscle is also known as myocardium
Cardiac muscle, also known as myocardium, is one of the three major categories of muscles in the human body, the other two being smooth muscle and skeletal muscle. It is an involuntary, striated muscle that constitutes the main tissue of the wall of the heart. The myocardium forms a thick middle layer of the heart wall, between the outer layer or pericardium and the inner layer or endocardium. The endocardium is not cardiac muscle but is made up of simple squamous epithelial cells that form the inner lining of the heart chambers and valves.
The myocardium is composed of individual cardiac muscle cells or cardiomyocytes, encased by collagen fibres and other substances that form the extracellular matrix. The functional unit of cardiomyocyte contraction is the sarcomere, which consists of thick (myosin) and thin (actin) filaments. The interactions between these filaments form the basis of the sliding filament theory. Each myocyte contains a single, centrally located nucleus surrounded by a cell membrane called the sarcolemma. The sarcolemma contains voltage-gated calcium channels, which are specialised ion channels that skeletal muscles do not possess.
Cardiac muscle cells contain branched fibres connected via intercalated discs that contain gap junctions and desmosomes. These interconnections allow the cardiomyocytes to contract together synchronously, enabling the heart to work as a pump. The primary function of the cardiac muscle is to pump blood into circulation by generating sufficient force. The contractile functions of the heart require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones.
The rise in calcium causes the cell's myofilaments to slide past each other in a process called excitation-contraction coupling. Within the myocardium, there are several sheets of cardiac muscle cells that wrap around the left ventricle closest to the endocardium. When these sheets contract in a coordinated manner, they allow the ventricle to squeeze in several directions simultaneously – longitudinally (becoming shorter from apex to base), radially (becoming narrower from side to side), and with a twisting motion (similar to wringing out a damp cloth) – to squeeze the maximum possible amount of blood out of the heart with each heartbeat.
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It is involuntary and striated
Cardiac muscle, also known as myocardium, is one of three major categories of muscles in the human body, the other two being smooth muscle and skeletal muscle. It is made up of sarcomeres, which allow for contractility.
Cardiac muscle is involuntary, meaning it operates without conscious control to maintain the heartbeat. The heart is able to contract with enough force to pump blood into circulation and supply the metabolic demands of the entire body. This is achieved through the coordinated contraction of cardiac muscle cells, or cardiomyocytes, which are connected by intercalated discs. These cells contain a high number of mitochondria and are striated, or banded, in appearance.
Striated muscle is a type of muscle tissue that is characterised by its striped or banded appearance. This is due to the arrangement of thick and thin filaments within the muscle cells. In cardiac muscle, these filaments are composed of myosin and actin, respectively. The thick and thin filaments interact to facilitate muscle contraction, which is essential for the pumping action of the heart.
The contractile functions of the heart are regulated by electrical impulses and require ATP, which can be obtained from various substrates, including fatty acids, carbohydrates, proteins, and ketones. The beating of the heart is set by specialised cardiomyocytes known as pacemaker cells, which are distributed throughout the heart. These cells carry the electrical impulses that trigger heart contractions and are responsible for maintaining the rhythm of the heartbeat.
In summary, cardiac muscle is involuntary and striated. Its involuntary nature ensures the continuous pumping of blood throughout the body, while its striated structure facilitates the contractile functions necessary for the heart's pumping action.
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It is responsible for pumping blood into circulation
The primary function of cardiac muscle is to pump blood into circulation by generating sufficient force. The heart is made up of three layers—the pericardium, myocardium, and endocardium. The myocardium, or cardiac muscle, forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium).
Cardiac muscle is composed of individual cardiac muscle cells, or cardiomyocytes, joined by intercalated discs. These cells are surrounded by an extracellular matrix produced by supporting fibroblast cells. The intercalated discs contain gap junctions and desmosomes, which allow cardiomyocytes to contract together synchronously, enabling the heart to work as a pump.
The functional unit of cardiomyocyte contraction is the sarcomere, which consists of thick (myosin) and thin (actin) filaments. The interactions between these filaments form the basis of the sliding filament theory. The sliding filament theory describes the process by which the cell's myofilaments slide past each other in a process called excitation-contraction coupling.
Cardiac muscle cells contain branched fibres that are connected via intercalated discs. These interconnections allow the cardiomyocytes to contract together synchronously, enabling the heart to pump blood. The contractile functions of the heart require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones.
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It is made up of sarcomeres and cardiomyocytes
Cardiac muscle, also known as the myocardium, is one of three major categories of muscles in the human body, the other two being smooth muscle and skeletal muscle. Cardiac muscle is made up of sarcomeres and cardiomyocytes, which work together to facilitate the pumping of blood through the circulatory system.
Cardiomyocytes are the individual cells that make up cardiac muscle. They are rectangular, branching cells, typically containing a single, centrally-located nucleus. This is in contrast to skeletal muscle cells, which often contain multiple nuclei. Cardiomyocytes contain a high number of mitochondria, which produce large amounts of adenosine triphosphate (ATP) and myoglobin to store oxygen, meeting the demands of muscle contraction. The individual cardiomyocyte is a tubular structure composed of chains of myofibrils, which are rod-like units within the cell.
Sarcomeres are the fundamental contractile units of muscle cells. They are composed of long proteins that organise into thick and thin filaments, called myofilaments. The thick filaments are composed of myosin, while the thin filaments are composed of actin. The interaction between these filaments forms the basis of the sliding filament theory, which describes muscular contraction. In this theory, active force is generated as actin filaments slide past the myosin filaments, resulting in the contraction of an individual sarcomere. This process is facilitated by the presence of calcium ions and requires ATP.
The structure of cardiac muscle allows for distinct features such as coordinated contraction and resistance to fatigue. Neighbouring cardiomyocytes are joined together at their ends by intercalated discs, creating a syncytium of cardiac cells. Gap junctions within these intercalated discs permit intercellular communication, allowing for the rapid transmission of action potentials and resulting in the synchronised contraction of cardiomyocytes. This electrical coupling between adjacent cardiomyocytes is vital for the proper functioning of the heart.
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It is one of three types of muscle tissues in the body
Cardiac muscle, also known as myocardium or heart muscle, is one of three types of muscle tissues in the body. The other two types are skeletal muscle and smooth muscle. Cardiac muscle is found in the heart and is responsible for pumping blood throughout the body. It is composed of individual cardiac muscle cells, called cardiomyocytes, which are joined by intercalated discs and encased in collagen fibres and other substances that form the extracellular matrix.
Cardiac muscle is an involuntary, striated muscle, meaning it operates without conscious control and has a banded appearance similar to skeletal muscle. The contractile functions of the heart require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones. Aerobic production is the core utilization process, although the heart may use anaerobic processes to a limited degree.
The cardiac action potential lasts approximately 200 ms and is divided into five phases: resting, upstroke, early repolarization, plateau, and final repolarization. Electrical stimulation triggers the release of calcium from the cell's internal calcium store, the sarcoplasmic reticulum, which causes the cell's myofilaments to slide past each other in a process called excitation-contraction coupling.
The heart wall is a three-layered structure, with a thick layer of myocardium sandwiched between the inner endocardium and the outer epicardium (also known as the visceral pericardium). The endocardium lines the cardiac chambers, covers the cardiac valves, and joins with the endothelium that lines the blood vessels connected to the heart. The outer epicardium forms part of the pericardial sac, which surrounds, protects, and lubricates the heart.
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Frequently asked questions
Cardiac muscle, also called the myocardium, is one of three major categories of muscles in the human body. It is made up of sarcomeres that allow for contractility.
The primary function of cardiac muscle is to pump blood into circulation by generating sufficient force. The contractile functions of the heart require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones.
Unlike skeletal muscle, cardiac muscle is under involuntary control. Cardiac muscle also forms the bulk of the heart, whereas skeletal muscle does not.
