Victor Forge
Skeletal muscles are one of the three types of vertebrate muscle tissue, the others being cardiac and smooth muscle. They are attached by tendons to bones and are responsible for initiating and stopping movement. Each skeletal muscle is made up of muscle fibres, or myocytes, which are bound together by various layers of connective tissue. Skeletal muscles are highly adaptive and can alter their size and biochemical makeup in response to changes in their environment. They are also responsible for maintaining body posture, controlling body temperature, and stabilising joints.
| Characteristics | Values |
|---|---|
| Type of muscle tissue | Skeletal muscle is one of the three types of vertebrate muscle tissue, the others being cardiac muscle and smooth muscle. |
| Attachment | Skeletal muscle is attached by tendons to bones of a skeleton. |
| Cells | Skeletal muscle cells are long, cylindrical, and multinucleated. |
| Tissue | Skeletal muscle tissue is striated, having a striped appearance due to the arrangement of sarcomeres. |
| Composition | Skeletal muscle is composed of muscle fibres, which are bound together by various layers of connective tissue. |
| Connective tissue | The three layers of connective tissue in skeletal muscle are epimysium, perimysium, and endomysium. |
| Nerve tissue | Skeletal muscle has an abundant supply of nerve tissue. |
| Blood vessels | Skeletal muscle has a rich supply of blood vessels. |
| Function | Skeletal muscle is responsible for producing movement, maintaining body posture, controlling body temperature, and stabilizing joints. |
| Contraction | Skeletal muscle can only contract and relax. |
| Types of fibres | Skeletal muscle contains Type I, Type IIa, and Type IIx fibres, each with different characteristics and functions. |
| Size | Skeletal muscle can vary considerably in size, shape, and arrangement of fibres. |
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What You'll Learn
Skeletal muscle composition
Skeletal muscle is the most common type of muscle in the human body. It comprises approximately 30% to 40% of an individual's total body mass. Skeletal muscle is a highly organised tissue made up of bundles of muscle fibres called myofibers, which contain several myofibrils. Each myofiber represents a muscle cell with its basic cellular unit, the sarcomere.
Myofibrils are composed of actin (thin filaments), myosin (thick filaments), and support proteins. The arrangement of actin and myosin gives skeletal muscle its microscopic striated appearance and creates functional units called sarcomeres. When viewed under electron microscopy, sarcomeres are arranged longitudinally and include the M line, Z disk, H band, A band, and I band. The Z line, or Z disk, is the terminal boundary of the sarcomere, where alpha-actinin acts as an anchor for the actin filaments. The M line is the central-most line of the sarcomere, where myosin filaments are anchored together through binding sites within the myosin filament. The H band contains the M line and is the central region of the sarcomere that contains only myosin filaments. The A band is a larger portion of the sarcomere that contains the entirety of the myosin fibres and includes regions of actin and myosin overlap. The I band covers the terminal regions of two adjacent sarcomeres and contains only actin filaments.
Bundles of myofibers form fascicles, and bundles of fascicles form muscle tissue. Each muscle fibre is composed of several hundred to several thousand myofibrils. Skeletal muscle fibres are striated, multinucleated cells ranging from 10 to 100 micrometers in diameter and many centimetres long. The nuclei are located in the cell's periphery, adjacent to the sarcolemma. The sarcolemma is a tubular sheath that encases and defines each muscle fibre, forming a barrier between extracellular and intracellular compartments.
Grossly, skeletal muscle fibres are made up of endomysium, perimysium, and epimysium, covering the sarcolemma; each muscle fibre is a layer of connective tissue called the endomysium. Capillaries and nerve tissue are present within the endomysium to supply the individual muscle fibres. Multiple muscle fibres join to form fascicles encased by another connective tissue covering known as the perimysium. The perimysium may surround anywhere from 10 to 100 fascicles. Muscle fascicles are further grouped to form a muscle encased by a fibrous tissue envelope called the epimysium.
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Types of muscle fibres
Skeletal muscle is one of the three types of vertebrate muscle tissue, the others being cardiac and smooth muscle. They are part of the voluntary muscular system and are attached by tendons to the bones of a skeleton. Skeletal muscles are responsible for producing movement, maintaining body posture, controlling body temperature, and stabilizing joints.
Skeletal muscles are made up of bundles of muscle fibres, also known as myofibers, which contain several myofibrils. Each myofiber represents a muscle cell with its basic cellular unit, the sarcomere. Bundles of myofibers form fascicles, and bundles of fascicles form muscle tissue.
Now, onto the types of muscle fibres:
Slow-Twitch Fibres (Type 1)
Slow-twitch fibres are characterised by their slower movement rates, response to neural inputs, and metabolic styles. They are also known as Type 1 fibres and are often associated with endurance activities requiring sustained muscle contractions over longer periods. These fibres have a higher density of mitochondria and myoglobin, giving them a red appearance. They rely primarily on aerobic metabolism for energy production, utilising both fats and carbohydrates as fuel sources.
Fast-Twitch Fibres (Type 2)
Fast-twitch fibres, or Type 2 fibres, are further classified into three subtypes: Type 2A, Type 2X, and Type 2B. These fibres are associated with powerful and rapid movements, such as sprinting or weight-lifting. Type IIb fibres, also known as fast glycolytic fibres, are the largest in diameter due to their high density of actin and myosin proteins. They contain fewer mitochondria and are termed white fibres due to their low myoglobin content. Fast-twitch fibres rely more on anaerobic glycolysis for energy production and have a higher rate of fatigue compared to slow-twitch fibres.
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Skeletal muscle functions
Skeletal muscles are the most common type of muscle in the human body, comprising 30% to 40% of total body mass. They are attached to the bones via tendons and are responsible for a wide range of movements and functions. These muscles are voluntary, meaning that an individual can control how and when they work. Skeletal muscles are also present in the tongue, diaphragm, eye socket, and upper oesophagus.
The primary function of skeletal muscles is to contract to produce movement. When these muscles contract, they shorten and pull on the bones, causing them to move. Skeletal muscles are also involved in initiating and stopping movement, such as when reaching for a book on a shelf, which involves the contraction of skeletal muscles in the neck, arm, and shoulder.
Another important function of skeletal muscles is to sustain body posture and position. They help to hold the body upright and maintain posture through constant slight adjustments. These muscles keep the bones stable and prevent skeletal damage and joint stability.
Skeletal muscles also play a role in maintaining body temperature. As they contract, they use energy, known as ATP, which generates heat. This heat production is particularly important in cold environments, where muscles are signalled to contract rapidly through shivering to generate warmth.
Additionally, skeletal muscles serve as a storage site for essential nutrients such as glycogen, amino acids, and proteins. They also act as a protective shield for organs, especially those in the abdomen, providing structural support and helping to bear their weight.
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Skeletal muscle disorders
Skeletal muscle, commonly referred to as muscle, is one of the three types of vertebrate muscle tissue, the others being cardiac and smooth muscle. Skeletal muscles are attached to bones by tendons and make up around 35% to 40% of body weight in humans. They are responsible for producing movement, maintaining body posture, controlling body temperature, and stabilizing joints.
- Back pain
- Arthritis
- Osteoporosis
- Tendonitis
- Gout
- Osteoarthritis
- Psoriatic arthritis
- Rheumatoid arthritis
Treatment options for musculoskeletal disorders include pain medications, physical therapy, and joint replacement surgery. Advanced drug delivery strategies for the treatment of musculoskeletal disorders may also involve therapeutic drugs (e.g., genes, small molecule therapeutics, and stem cells), novel delivery vehicles (e.g., three-dimensional printing and tissue engineering techniques), and innovative delivery approaches (e.g., multi-drug delivery and smart stimuli-responsive delivery).
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Skeletal muscle vs. other muscle types
Skeletal muscle is the most common type of muscle in the human body, accounting for between 30% and 40% of total body mass. These muscles are attached to bones by tendons and allow for a wide range of movements. Skeletal muscles are also known as striated muscles due to their striped appearance, which is caused by the arrangement of sarcomeres. These muscles are voluntary, meaning that their movement can be consciously controlled. They consist of flexible muscle fibres that contract to enable movement and can range from less than half an inch to over 3 inches in diameter. Each skeletal muscle can contain thousands of fibres, and these fibres are surrounded by connective tissue known as fascia. Skeletal muscles play a vital role in everyday activities such as breathing, eating, and moving.
Cardiac muscle is the second type of muscle tissue. These muscles are found in the walls of the heart and are under involuntary control. It contracts and relaxes to pump blood through the cardiovascular system. Cardiac muscle also has a striped appearance, although it is distinct from skeletal muscle. Cardiac muscle cells are much smaller than skeletal muscle cells and are not attached to bones.
Smooth muscle is the third type of muscle tissue. These muscles are also involuntary and are found in the walls of hollow visceral organs such as the liver, pancreas, and intestines. They are spindle-shaped and lack the striped appearance of skeletal and cardiac muscles. Smooth muscles are responsible for various functions, including digestion and the transportation of food through the digestive tract.
While skeletal muscles are primarily responsible for movement and are under voluntary control, cardiac and smooth muscles have distinct functions and are involuntary. Additionally, skeletal and cardiac muscles exhibit a striped pattern, while smooth muscles do not. The different types of muscles work together to maintain the body's overall health and functionality.
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Frequently asked questions
Skeletal muscle is one of the three types of vertebrate muscle tissue, the others being cardiac muscle and smooth muscle. They are part of the voluntary muscular system and are attached by tendons to bones.
Skeletal muscles are made of muscle fibres, also known as myocytes, which are bound together by various layers of connective tissue. Each muscle fibre is composed of several hundred to several thousand myofibrils. Myofibrils are composed of actin (thin filaments), myosin (thick filaments), and support proteins.
Skeletal muscles are responsible for producing movement, maintaining body posture, controlling body temperature, and stabilising joints. They are also involved in protecting organs and storing glycogen and amino acids.
Skeletal muscles work in pairs, with one muscle contracting and the other relaxing to allow for movement in different directions. The contraction of skeletal muscles is initiated by signals from the autonomic nervous system and nerve cells, which cause the muscles to shorten and pull on bones, resulting in movement.
