Skeletal Muscle Structure
Components and Attachments
Introduction
A skeletal muscle is an organ made mostly of muscle fibers (cells), blood vessels, nerves, and three layers of connective tissue. Muscle fibers contract and generate force, while adjacent blood vessels and nerves sustain and regulate their activity. Collagen fibers within the connective tissue layers bind muscle components, maintain muscle shape, and transfer tension during contraction.
Connective Tissue Layers
The epimysium is a thick layer of connective tissue that surrounds an entire muscle, consisting primarily of irregularly arranged collagen fibers. During muscle contraction, it transfers tension, maintains the muscle’s shape, and decreases friction with other structures.
The perimysium extends inward from the epimysium, and its collagen fibers wrap groups of muscle fibers into bundles called fascicles. The muscle fibers in each fascicle contract together and pull in the same direction. The perimysium also helps transfer this force through the muscle and provides routes for blood vessels and nerves to reach the muscle fibers.
The endomysium is the innermost connective tissue layer. This loose network of collagen and reticular fibers extends into each fascicle from the perimysium, surrounding individual muscle fibers and filling the spaces between them.
Support Structures
Arteries, veins, and nerves pass through the connective tissue layers to support the muscle fibers. The nerves carry motor and sensory signals between the central nervous system and the muscle. Motor signals cause muscle cells to contract, while sensory signals allow the brain and spinal cord to monitor and adjust movements. Arteries deliver oxygen and nutrients to muscle fibers through capillaries, and veins remove carbon dioxide (CO₂) and other metabolic waste products.
Structure of a Skeletal Muscle
Muscle Attachments
Most skeletal muscles attach to bones via tendons. These cord-like bands of dense collagenous connective tissue become continuous with the muscle’s epimysium, perimysium, and endomysium and fuse with the periosteum of a bone. Contraction of the muscle fibers transfers tension through these connective tissues to the tendon and periosteum, producing bone movement.
Some skeletal muscles attach to broad, flat sheets of connective tissue called aponeuroses. Like tendons, aponeuroses are composed of collagen and connect muscles to bone, fascia (connective tissue sheets), other muscles, or skin. Aponeuroses distribute muscular forces across broad areas and contribute to bodily support and stability. Prominent aponeurotic structures occur in the anterior abdominal wall and lower back. The thoracolumbar fascia is a multilayered fascial complex with aponeurotic components. It provides attachment for muscles including the latissimus dorsi and helps transmit forces through the lower back.
Assessment
Skeletal Muscle Identification and Function Quiz
Select the question mark that points to the structure described below.
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References and Attributions
Cleveland Clinic – “Skeletal Muscle.”
Frontiers in Pathology – “The Structure and Role of Intramuscular Connective Tissue in Muscle Function.”
NIH: National Library of Medicine – “Anatomy, Fascia Layers.”
NIH: National Library of Medicine – “Anatomy of Skeletal Muscle and Its Vascular Supply.”
NIH: National Library of Medicine – “Anatomy, Tendons.”
NIH: National Library of Medicine – “Connecting muscles to tendons: tendons and musculoskeletal development in flies and vertebrates.”
NIH: National Library of Medicine – “The development of the myotendinous junction. A review.”
NIH: National Library of Medicine – “The Structure and Role of Intramuscular Connective Tissue in Muscle Function.”
NIH: National Library of Medicine – “The Myotendinous Junction—A Vulnerable Companion in Sports. A Narrative Review.”
Science Direct – “Muscle Fascicle.”
Science Direct – “Perimysium.”