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The human heart is a powerful organ, beating about 100,000 times a day. Unlike other muscles in the body, the heart rarely tires. This is because cardiac muscle is made up of a special type of cell called cardiomyocytes, which are highly resistant to fatigue. Cardiac muscle also has a large number of mitochondria, which are the energy powerhouses of the cell, meaning the heart has a constant supply of energy.
| Characteristics | Values |
|---|---|
| Cardiac muscle composition | Consists of special cells called cardiomyocytes |
| Cardiomyocytes | Highly resistant to fatigue |
| Mitochondria | Cardiac muscle has more mitochondria than skeletal muscle |
| Energy | Always some energy being transferred to the muscle while more is being derived from caloric intake |
| Cardiac muscle vs skeletal muscle | Cardiac muscle contracts without nerve supply, making it incapable of voluntary and purposeful movements |
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What You'll Learn
Cardiac muscle is made of special cells called cardiomyocytes
The heart is an incredibly powerful organ that beats about 100,000 times per day. The force used by the heart to pump blood around the body is comparable to the energy it takes to squeeze a tennis ball. The heart is made of cardiac muscle, which consists of special cells called cardiomyocytes. These cells are responsible for keeping the heart pumping and blood circulating throughout the body.
Cardiac muscle cells are striated, branched, and contain many mitochondria. They are under involuntary control, meaning their movements are automatic and a person cannot control them. Each cardiomyocyte contains a single, centrally located nucleus surrounded by a cell membrane called the sarcolemma. The sarcolemma contains voltage-gated calcium channels, specialized ion channels that skeletal muscle does not possess.
The functional unit of cardiomyocyte contraction is the sarcomere, which consists of thick (myosin) and thin (actin) filaments. When a cardiac muscle cell contracts, the myosin filament pulls the actin filaments toward each other, causing the cell to shrink. The cell uses ATP to power this contraction. The sarcolemma of cardiac muscle cells also contains transverse tubules (t-tubules), which are highly branched invaginations that function in excitation-contraction coupling, action potential initiation and regulation, maintaining the resting membrane potential, and signal transduction.
Cardiomyocytes are the only cells in the body that can contract without nerve supply, making them incapable of voluntary and purposeful movements. This unique ability allows the heart to beat constantly without tiring.
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Cardiomyocytes are highly resistant to fatigue
The heart is an incredibly powerful organ, beating about 100,000 times a day. With so many repetitions, it is a wonder that it does not burn out. The heart is made of cardiac muscle, which consists of special cells called cardiomyocytes. Unlike other muscle cells in the body, cardiomyocytes are highly resistant to fatigue.
Cardiomyocytes are primarily powered by mitochondria, which are the energy powerhouses of the cell. They have a high density of mitochondria, up to 10 times that of skeletal muscle cells, which skyrockets their energy output. This abundance of mitochondria means that cardiomyocytes can produce a large amount of adenosine triphosphate (ATP), the energy currency of cells, efficiently over long periods.
Cardiomyocytes have also evolved to have an enhanced blood supply, being better than ordinary muscle cells at extracting oxygen from the blood. This is facilitated by the high concentration of myoglobin, a protein that stores oxygen, providing a ready supply for use during aerobic respiration. This is crucial because it ensures the cells have enough oxygen to produce energy even when blood flow may be temporarily reduced.
Additionally, the heart is flexible in terms of fuel, able to consume glucose, free fatty acids, and lactate. This adaptability in fuel sources further contributes to the resistance to fatigue in cardiomyocytes. Furthermore, cardiomyocytes contain T-tubules, pouches of cell membrane that improve the efficiency of contraction. The T-tubules in cardiac muscle are bigger and wider than those in skeletal muscle, contributing to the efficient functioning of the heart.
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Cardiac muscle has a lot of mitochondria
The human heart is a powerful organ, beating about 100,000 times a day. This force is comparable to the energy it takes to squeeze a tennis ball, which is similar to the force the heart exerts with each beat to pump blood around the body. Cardiac muscle resists fatigue because it has a lot of mitochondria.
Mitochondria are the energy factories for all cells, producing energy in the form of ATP through oxidative phosphorylation. They are the means of providing energy for the constant activity of the heart. The heart is constantly contracting and relaxing, and it needs a lot of energy to pump blood through the circulatory system. Therefore, it contains more mitochondria than skeletal muscle to produce a high level of ATP.
Cardiac muscle consists of special cells called cardiomyocytes, which are highly resistant to fatigue. Cardiomyocytes are primarily powered by mitochondria. Unlike other muscle cells in the body, cardiomyocytes contract without nerve supply, making them incapable of voluntary and purposeful movements. This means that the heart can beat constantly without tiring.
The high number of mitochondria in cardiac muscle is a trait that humans have evolved to increase their chances of survival. The mitochondria in the heart also monitor complex information from the environment and intracellular milieu, including the presence or absence of growth factors, oxygen, reactive oxygen species, and DNA damage.
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Cardiac muscle can contract without nerve supply
The cardiac muscle, or heart, is an incredibly powerful organ that beats about 100,000 times a day. Unlike skeletal muscles, the heart is resistant to fatigue. This is because the heart is made of cardiac muscle, which consists of special cells called cardiomyocytes. These cells are highly resistant to fatigue and are primarily powered by mitochondria, the energy house of the cell.
Cardiac muscle tissue has specialized cells called pacemaker cells, primarily located in the sinoatrial (SA) node, which acts as the heart's natural pacemaker. These pacemaker cells can generate electrical impulses autonomously due to their unique ion channels. This ability to generate electrical impulses spontaneously is called automaticity.
Automaticity allows the heart to maintain a rhythmic heartbeat, even without nervous system input. The SA node produces rhythmic electrical signals that spread through the heart, causing the atria to contract and the electrical impulse to reach the atrioventricular (AV) node. From the AV node, the electrical impulse travels down the bundle of His, through the bundle branches, and into the Purkinje fibers, which distribute the impulse throughout the ventricles. This coordinated spread of electrical impulses ensures that the heart contracts in a rhythmic and efficient manner, allowing it to pump blood effectively without requiring direct neural stimulation.
While automaticity enables independent contraction, the heart rate can be adjusted by external signals from the nervous and endocrine systems. This means that even if the nerves connecting the heart to the central nervous system are damaged or severed, the heart can still beat rhythmically and continuously.
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Cardiac muscle is different from skeletal muscle
The human body has three major categories of muscles: cardiac, smooth, and skeletal. Cardiac muscles are found in the heart and are self-stimulating, with an intermediate speed of contraction and energy requirements. They are responsible for performing involuntary muscular movements.
Skeletal muscles, on the other hand, are attached to bones all over the body. They do not self-stimulate and have a high speed of contraction and energy requirements. These muscles are responsible for voluntary muscular movements.
Cardiac muscle, or myocardium, is made up of special cells called cardiomyocytes, which are highly resistant to fatigue. This is because they have more mitochondria than skeletal muscle, providing them with a greater energy supply. The sarcolemma of cardiac muscle cells also contains voltage-gated calcium channels, which skeletal muscles do not possess. These calcium channels trigger calcium influx when they are opened, which is important for muscle contraction.
The cardiac muscle must contract with enough force to pump blood into circulation and supply blood to the body's metabolic demands. This is a critical and constant function that leaves no room for muscle fatigue or rest days. The cardiac muscle cells generate most of their ATP from the β-oxidation of fatty acids.
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Frequently asked questions
Unlike other muscles in the body, the heart rarely tires.
The heart is made of cardiac muscle, which consists of special cells called cardiomyocytes that are highly resistant to fatigue.
Cardiomyocytes are a type of cell that can contract without a nerve supply. While this means they are incapable of voluntary and purposeful movements, they are perfect for the constant beating of the heart.
Like skeletal muscle, cardiac muscle is powered by mitochondria. However, cardiac muscle has a much higher volume of mitochondria, with estimates ranging from 30-35% of the total volume of the heart.
While the heart is resistant to fatigue, it is not immune to the effects of ageing. As we grow older, the heart slows down, its vessels stiffen, and it needs to work harder to pump blood around the body.
