Skeletal muscle
Striated, multinucleated tissue enabling voluntary movement and posture.
Skeletal muscle is one of the three types of vertebrate muscle tissue, alongside cardiac muscle and smooth muscle. It is part of the musculoskeletal system and is typically attached by tendons to the bones of a skeleton. Skeletal muscle comprises about 35% of the human body by weight and is responsible for producing movement, maintaining body posture, controlling body temperature, and stabilizing joints. It also functions as an endocrine organ, secreting a variety of proteins, lipids, amino acids, metabolites, and small RNAs.
The cells of skeletal muscle, known as myocytes or muscle fibers, are much longer than those in other muscle types and have a striped (striated) appearance due to the arrangement of sarcomeres. These fibers are formed during development when myoblasts fuse together, creating long, multinucleated cells. The nuclei, called myonuclei, are positioned along the inner surface of the cell membrane. Each fiber contains numerous mitochondria to supply energy. Within a fiber, myofibrils are composed of repeating sarcomeres, the basic contractile units made of actin and myosin filaments. Muscle contraction is powered by adenosine triphosphate (ATP), which is produced primarily through the oxidation of fats and carbohydrates, though fast-twitch fibers also rely on anaerobic reactions.
A skeletal muscle is organized into bundles called fascicles, each surrounded by connective tissue layers known as fascia. The muscle itself and each individual fiber are also encased in fascia. While myocytes make up the vast majority of a muscle’s volume, a significant number of smaller mononuclear cells are also present, including endothelial cells, macrophages, and neutrophils. In fact, myonuclei may account for only about half of all nuclei in skeletal muscle, with the remainder coming from these resident and infiltrating cells. Research on skeletal muscle focuses not only on the contractile fibers but also on these mononuclear cells and the muscle’s endocrine functions.
- field
- Anatomy, Physiology
- known_for
- Voluntary movement, striated appearance, multinucleated muscle fibers
- percentage_of_body_weight
- ~35% in humans
- nuclei_distribution
- ~50% myonuclei, ~50% mononuclear cell nuclei
Lore & Background
Skeletal muscle cells, also called muscle fibers, are formed from the fusion of developmental myoblasts during myogenesis, resulting in long multinucleated cells. These fibers contain myofibrils composed of actin and myosin filaments arranged in repeating units called sarcomeres, which are the basic contractile units. Muscles are powered by oxidation of fats and carbohydrates, with anaerobic reactions used particularly by fast twitch fibers, producing ATP for myosin head movement. A skeletal muscle contains multiple fascicles—bundles of muscle fibers—each surrounded by connective tissue layers: endomysium, perimysium, and epimysium. Tendons attach muscles to bones at the myotendinous junction. Sensory receptors include muscle spindles (stretch receptors) and Golgi tendon organs (proprioceptors at the myotendinous junction). Muscle architecture varies, with parallel and pennate arrangements affecting force generation and speed.
Reader's Guide
Skeletal muscle is fundamental to vertebrate movement and homeostasis. Its striated appearance, due to sarcomere arrangement, distinguishes it from cardiac and smooth muscle. The multinucleated nature of its fibers, arising from myoblast fusion, allows for large-scale protein synthesis needed for contraction. The presence of both myonuclei and mononuclear cells (including endothelial cells, fibro-adipogenic progenitors, pericytes, and immune cells) highlights a complex cellular environment. Research focuses on muscle fibers, mononuclear cell types, and endocrine functions. The ability of satellite cells to provide additional myonuclei for growth or repair underscores muscle plasticity. Understanding skeletal muscle is crucial for fields from sports science to pathology, as it comprises a significant portion of body mass and influences metabolism, posture, and joint stability.
Did You Know?
- Skeletal muscle fibers are multinucleated, with nuclei called myonuclei located along the inside of the cell membrane.
- Skeletal muscle comprises about 35% of the human body by weight, and in Western populations, men have on average around 61% more skeletal muscle than women.
More in Human Anatomy 1-24
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record