Dominic Stone
Skeletal muscles are one of the three types of muscles in the body, the other two being cardiac and smooth muscles. They are attached to the bones by tendons and allow us to perform a wide range of movements and functions. These muscles are voluntary, meaning that we control how and when they work. Skeletal muscles are also responsible for maintaining body posture, controlling body temperature, and stabilising joints. They make up around 30% to 40% of our total body mass and consist of flexible muscle fibres that contract and expand, enabling us to move our bones and perform various physical activities.
| Characteristics | Values |
|---|---|
| Types of muscle tissue | There are three types of muscle tissue in the body: skeletal, cardiac, and smooth muscle. |
| Appearance | Skeletal muscles are striated, or striped. |
| Muscle composition | Skeletal muscles are made up of muscle fibres, or myocytes, which are composed of myofibrils. |
| Myofibril composition | Myofibrils are composed of actin and myosin filaments, or myofilaments. |
| Sarcomere composition | Sarcomeres are made up of actin and myosin filaments, with regulatory proteins such as troponin and tropomyosin. |
| Sarcomere structure | Sarcomeres have a central M line, with attached myosin filaments, and a border of Z lines, from which actin filaments project. |
| Muscle fibre size | Muscle fibres range from 10 to 100 micrometres in diameter and can be several centimetres long. |
| Muscle fibre colour | Skeletal muscle fibres are red and white. |
| Number of muscle fibres | Each muscle contains several hundred to several thousand muscle fibres. |
| Connective tissue | Each muscle has three layers of connective tissue: epimysium, perimysium, and endomysium. |
| Muscle function | Skeletal muscles enable movement, maintain body posture, control body temperature, stabilise joints, and protect organs. |
| Proportion of body weight | Skeletal muscles make up around 30-40% of body weight. |
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What You'll Learn
Skeletal muscle composition
Skeletal muscles are 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 bones. Skeletal muscles comprise 30% to 40% of total body mass in humans, with males having more skeletal muscle mass than females. They are made up of thousands of small muscle fibres woven together, which contract and press together to move the body and its organs.
Each muscle fibre is composed of several hundred to several thousand myofibrils, which are made up 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. Sarcomeres are the basic functional, contractile units of the muscle fibre, necessary for muscle contraction. The sarcomere consists of a central M line, with thick myosin filaments attached to it on either side, forming a dark A band. The sarcomere is bordered by the Z-line, which serves as the site of origin of the thin actin filaments that project towards each other, partially overlapping the myosin filaments. Regulatory proteins such as troponin C, I, T, and tropomyosin play a key role in the myofilaments sliding mechanism leading to contraction.
Skeletal muscle fibres are 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, which is a tubular sheath that encases and defines each muscle fibre. The sarcolemma is made up of a plasma membrane and a polysaccharide coating that fuses with tendon fibres. Skeletal muscle fibres are also composed of three layers of connective tissue, or sheaths, that surround the fibres: the outermost layer is the epimysium, the middle layer is the perimysium, and the innermost layer is the endomysium. The endomysium contains capillaries and nerve tissue, which supply the individual muscle fibres with oxygen, nutrients, and neural signals.
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Skeletal muscle functions
Skeletal muscles are responsible for all our voluntary movements and functions. They are attached to our bones by tendons, which are fibrous connective tissues. These muscles make up 30-40% of our total body mass and consist of flexible muscle fibres that contract and expand, allowing us to perform a wide range of movements.
Each skeletal muscle contains multiple fascicles, or bundles of muscle fibres. These fibres are composed of myofibrils, which are made up of actin and myosin filaments, or myofilaments. The arrangement of these filaments gives skeletal muscles their striated, or striped, appearance. The striations are patterns of red and white lines, with the red colour coming from blood vessels and the white from other muscle components.
The main functions of skeletal muscles include:
- Producing movement: Skeletal muscles contract and expand to generate force and power, enabling us to move our bodies and perform daily activities.
- Maintaining body posture and position: Some skeletal muscles contract quickly and use short bursts of energy (fast-twitch muscles), while others, like back muscles, move slowly to help with posture.
- Controlling body temperature: Skeletal muscles produce body heat as a by-product of muscular activity. In extreme cold, muscles contract through shivering to generate heat.
- Stabilising joints: Skeletal muscles work with tendons and ligaments to support our weight and stabilise joints.
- Protecting organs: These muscles act as a shield, protecting organs, especially those in the abdomen, and supporting their weight.
- Storing nutrients: Skeletal muscles store glycogen and amino acids, which can be released for energy during activity or starvation. They also store essential substrates such as carbohydrates and amino acids, which can be used by different organs to synthesise organ-specific proteins.
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Skeletal muscle movement
Skeletal muscles are the most common type of muscles in the human body, comprising 30% to 40% of total body mass. They are voluntary muscles, meaning that we can control how and when they move. They are attached to bones by tendons, which are tough connective tissues. Skeletal muscles allow us to perform a wide range of movements, from breathing and swallowing to reaching for a book on a shelf.
Each skeletal muscle consists of various integrated tissues, including muscle fibres, blood vessels, nerve fibres, and connective tissue. The muscle fibres are composed of myofibrils, which are made up of actin (thin filaments), myosin (thick filaments), and support proteins. The arrangement of these filaments gives skeletal muscle its striated appearance and creates functional units called sarcomeres.
The sarcomere consists of a central M-line with thick myosin filaments attached on either side, forming the dark A-band. The sarcomere is bordered by the Z-line, which is the origin of the thin actin filaments that project towards and overlap with the myosin filaments. Regulatory proteins such as troponin and tropomyosin play a key role in the sliding mechanism of the filaments during muscle contraction.
The muscle fibres are organised into individual bundles called fascicles by the middle layer of connective tissue, the perimysium. The nervous system activates a subset of muscle fibres within a fascicle to trigger specific movements. Each muscle fibre is encased in a thin connective tissue layer of collagen and reticular fibres called the endomysium, which contains extracellular fluid and nutrients supplied by blood to the muscle tissue.
When a skeletal muscle contracts, the tension created by the contraction of muscle fibres is transferred through the mysia (connective tissue layers) to the tendon and then to the periosteum, pulling on the bone for movement. Skeletal muscle contraction begins at the neuromuscular junction, the synapse between a motoneuron and a muscle fibre. The release of acetylcholine (ACh) at the neuromuscular junction triggers the muscle fibre to contract.
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Skeletal muscle anatomy
Skeletal muscles are one of the three types of vertebrate muscle tissue, the others being cardiac and smooth muscle. They are part of the voluntary muscular system, which means that they move when you think about moving. They are attached to bones by tendons, which are fibrous connective tissues. Skeletal muscles make up around 30% to 40% of body weight in healthy young adults, with males having on average around 61% more skeletal muscle than females.
Skeletal muscles are primarily made of muscle fibres, which are bundles of lots of proteins called myofibrils. Each myofibril contains smaller protein structures called sarcomeres, which have light and dark areas, creating patterns of red and white lines called striation. Skeletal muscles are often referred to as striated muscles due to this striped appearance. The sarcomeres allow the muscle fibres to contract and slide across each other so that the muscle shortens. Each muscle can contain thousands of fibres, and each fibre is composed of several hundred to several thousand myofibrils.
The muscle fibres are surrounded by three layers of connective tissue that support the muscle: the epimysium, perimysium, and endomysium. The epimysium is the outermost layer of dense, irregular connective tissue that surrounds the entire muscle. The perimysium is the middle layer of connective tissue that surrounds bundles of muscle fibres. The endomysium is the inner layer of connective tissue that surrounds individual muscle fibres.
Skeletal muscles have nerve fibres and blood vessels that bring in oxygen and nutrients and remove waste. The primary artery supplying blood to a skeletal muscle generally courses parallel to the longitudinal axis of the muscle fibre. The primary artery gives off tributaries known as feed arteries, which run perpendicular to the primary artery and proceed towards the perimysium.
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Skeletal muscle health
Skeletal muscles are the most common type of muscle in the body, comprising 30% to 40% of total body mass. They are attached to bones by tendons, or tough bands of connective tissue, and allow us to perform a wide range of movements and functions. These include breathing, eating, and moving our bones. Skeletal muscles are voluntary, meaning we control how and when they work.
Skeletal muscle fibres are striated, multinucleated cells ranging from 10 to 100 micrometers in diameter and many centimetres long. They are made up of endomysium, perimysium, and epimysium, covering the sarcolemma. Each muscle fibre is composed of several hundred to several thousand myofibrils, which are made up 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.
The main functions of skeletal muscle include contracting to produce movement, sustaining body posture and position, maintaining body temperature, storing nutrients, and stabilising joints. Skeletal muscle also contributes to basal energy metabolism, serving as a storage site for essential substrates such as carbohydrates and amino acids.
Given the vital role skeletal muscles play in everyday activities, it is important to keep them strong and healthy. Aging, chronic diseases, and strenuous exercise can lead to health problems associated with skeletal muscle, including muscle atrophy, loss of muscle mass and strength, and metabolic disorders. Various natural products, such as resveratrol, quercetin, ursolic acid, ecdysone, and vitamin D, have been reported to protect or regulate skeletal muscle health.
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Frequently asked questions
Skeletal muscles are the muscles that connect to your bones and allow you to perform a wide range of movements and functions. They are part of the voluntary muscular system and are controlled by the somatic nervous system.
Skeletal muscles are made of muscle fibres, which are composed of myofibrils. Myofibrils are made up of actin and myosin filaments called myofilaments, repeated in units called sarcomeres. Each muscle has three layers of connective tissue that support it: epimysium, perimysium, and endomysium.
Skeletal muscles enable humans to move and perform daily activities. They also help to sustain body posture and position, maintain body temperature, store nutrients, and stabilise joints.
