Dominic Stone
Striated muscle, also known as skeletal muscle, is the most common type of muscle in the human body, comprising 30% to 40% of total body mass. It is marked by transverse dark and light bands and is made up of elongated, multinucleated fibres. Skeletal muscles are attached to the bones and enable a wide range of movements, including breathing, eating, and maintaining posture. They are under voluntary control, meaning individuals can decide how and when they work. Cardiac muscle is another type of striated muscle, exclusively found in the heart, and responsible for heart contractions and pumping blood throughout the body.
| Characteristics | Values |
|---|---|
| Appearance | Striped or striated due to light and dark bands |
| Types | Skeletal muscle, cardiac muscle, and arthropod muscle |
| Tissue structure | Repeating functional units called sarcomeres |
| Tissue composition | T-tubules, sarcoplasmic reticulum, sarcolemma, sarcoplasm |
| Muscle fibre composition | Actin and myosin myofilaments |
| Muscle fibre shape | Cylindrical with blunt ends |
| Muscle fibre thickness | 20-100 µm |
| Muscle fibre length | Up to 20 cm |
| Control | Voluntary |
| Function | Create force and contract |
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What You'll Learn
Skeletal muscle
The muscle fibres are formed from the fusion of developmental myoblasts in a process called myogenesis, resulting in long multinucleated cells. Skeletal muscle cells have many nuclei, and these nuclei are located along the inside of the cell membrane. Each muscle fibre can contain hundreds to thousands of nuclei, which are necessary for the production of large amounts of proteins and enzymes for the cell's normal functioning.
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Cardiac muscle
Striated muscle tissue is marked by transverse dark and light bands and is made up of elongated, multinucleated fibres. It includes skeletal muscle, cardiac muscle, and most muscle tissue in arthropods.
The cardiac muscle is responsible for the contractility of the heart and, therefore, the pumping action. The primary function of the cardiac muscle is to pump oxygenated 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 heart may use anaerobic processes in a limited capacity.
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Striated muscle appearance
Striated muscle tissue is characterised by transverse dark and light bands, giving it a striped appearance. This appearance is due to the presence of repeating functional units called sarcomeres, which are visible along the muscle fibres under a microscope. The two types of striated muscle tissue are skeletal muscle and cardiac muscle, both of which have a striated appearance due to their densely packed myofibrils. Skeletal muscle fibres are red and white and are typically 20-100 µm thick and up to 20 cm long. They are surrounded by endomysium, forming the primary bundle, which is the functional unit of the muscle. Groups of primary bundles are then wrapped by the perimysium to form secondary bundles. The entire skeletal muscle is enclosed by epimysium and lies within its fascia, a tight connective tissue that separates it from surrounding structures. Cardiac muscle cells, on the other hand, are smaller, typically measuring 10-20 µm in thickness and 50-100 µm in length. They have a complex structure with myofibrils that do not run strictly parallel to each other but rather branch out.
The striated appearance of skeletal and cardiac muscles serves an important functional purpose. The dark and light bands correspond to areas of the muscle that exhibit different levels of light refraction, which is essential for muscle contraction. The bands also help differentiate striated muscles from smooth muscles, which lack the banded appearance due to the absence of sarcomeres. Smooth muscles have a different structure with spindle-like fibres and tapered ends, in contrast to the cylindrical shape of striated muscle fibres.
The appearance of skeletal muscle can vary depending on its condition. Skeletal muscles are susceptible to various conditions, ranging from mild injuries to serious or even life-threatening myopathies (diseases affecting skeletal muscles). Maintaining strong and healthy skeletal muscles is crucial as they comprise 30% to 40% of an individual's total body mass and enable a wide range of movements and functions.
Additionally, the appearance of striated muscles can be influenced by their regeneration process. Skeletal muscles have a unique ability to regenerate due to the presence of satellite cells, which are dormant in healthy muscle tissue. This regeneration process involves three phases: the inflammatory response, the activation and differentiation of satellite cells, and the maturation and remodelling of newly formed myofibrils.
In summary, the appearance of striated muscles, specifically skeletal and cardiac muscles, is characterised by transverse dark and light bands, resulting in a striped pattern. This visual distinction is a result of the underlying structure and function of these muscle fibres, particularly the presence of sarcomeres and densely packed myofibrils. The appearance of striated muscles can be impacted by various factors, including their condition, regeneration capabilities, and surrounding connective tissues.
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Muscle contractions
Striated muscle tissue is a type of muscle tissue that features repeating functional units called sarcomeres. These sarcomeres are responsible for the transverse dark and light bands that give striated muscle its distinctive appearance under a microscope. The two types of striated muscle are skeletal muscle and cardiac muscle.
Skeletal muscle is the most common type of muscle in the human body, comprising 30% to 40% of total body mass. These muscles are attached to bones and enable a wide range of movements and functions. They are also known as voluntary muscles, meaning that individuals have control over how and when they move. Skeletal muscle fibres are red and white and are often referred to as striated muscles due to their striped appearance.
Cardiac muscle, on the other hand, comprises the heart and is responsible for pumping blood throughout the body. Both skeletal and cardiac muscles are regulated by calcium ions (Ca2+), which are released from the sarcoplasmic reticulum and bind to troponin (Tn) on the actin filament. This binding process releases tropomyosin (Tm) from its position, allowing the interaction of myosin heads with actin. The actomyosin contractile apparatus is both calcium- and phosphorylation-dependent, and the restoration of basal calcium levels returns an actively contracting muscle to a non-contractile state.
The process of striated muscle contraction involves force generation within the striated muscle tissue, resulting in increased force exerted on the tendons. This force generation is achieved through the actin/myosin complex activity, which converts chemical energy into mechanical energy via ATP hydrolysis. Once the active sites of actin are exposed through calcium binding to the troponin complex, the myosin complex bound to ADP can bind to actin, and the myosin head can pivot. This pivoting action pulls the thin actin and thick myosin filaments past each other, resulting in muscle contraction.
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Muscle regeneration
Skeletal muscle, also known as striated muscle, is the most common type of muscle in the human body, comprising 30% to 40% of total body mass. It is made up of elongated, multinucleated fibres that exhibit a striated appearance under a microscope due to the presence of transverse dark and light bands. These muscles are under voluntary control and enable a wide range of movements, including breathing, eating, and maintaining posture.
Striated muscle, particularly skeletal muscle, has an impressive ability to regenerate new muscle fibres after injury or degenerative diseases such as muscular dystrophy. This regeneration process primarily relies on satellite cells, a type of mononucleated quiescent cell found beneath the basal lamina of skeletal muscles. When muscle damage occurs, the following steps initiate the regeneration process:
- Inflammatory Response: Macrophages induce phagocytosis to clear the damaged muscle fibres and cell debris. They also secrete anti-inflammatory cytokines to resolve the inflammation.
- Activation, Differentiation, and Fusion of Satellite Cells: Macrophages facilitate the proliferation and differentiation of satellite cells. These cells re-enter the cell cycle to multiply and then differentiate into myoblasts.
- Maturation and Remodelling of New Myofibrils: The newly formed myoblasts mature and remodel to regenerate and repair the damaged muscle fibres.
In addition to satellite cells, other cell types contribute to muscle regeneration. Regulatory T cells (Treg) play a crucial role in regulating the inflammatory response and influencing the behaviour of satellite cells. Fibro-adipogenic progenitors (FAPs) can promote efficient muscle regeneration or contribute to fibrotic accumulation, depending on environmental signals. Neural stem cells have also been shown to differentiate into skeletal muscle when cocultured with skeletal myoblasts or transplanted into regenerating skeletal muscle.
While striated muscle, including both skeletal and cardiac muscle, has some regenerative capacity, they differ in their effectiveness. Skeletal muscle regenerates more efficiently due to the presence of satellite cells, which are absent in cardiac muscle. Smooth muscle, on the other hand, has the greatest capacity for regeneration among muscle cell types due to its ability to divide and increase in number.
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Frequently asked questions
Striated muscles are muscles that have a striped appearance due to their light and dark bands. They are made up of elongated, multinucleated fibres.
There are two types of striated muscle: skeletal muscle and cardiac muscle. Skeletal muscles are attached to the bones and are under voluntary control, whereas cardiac muscles are found exclusively in the muscular walls of the heart and are involuntary.
The main function of striated muscle tissue is to create force and
Smooth muscle tissue is not striated as it does not contain sarcomeres. It is found in hollow structures such as the walls of intestines or blood vessels. Striated muscle tissue has more mitochondria than smooth muscle and skeletal muscle is able to regenerate better than cardiac muscle.
