20.5: Skeletal Muscle Anatomy

Skeletal muscle is the most abundant type of muscle in the body. Tendons are the connective tissue that attaches skeletal muscle to bones. Skeletal muscles pull on tendons, which in turn pull on bones to carry out voluntary movements.

Skeletal muscles are surrounded by a layer of connective tissue called epimysium, which helps protect the muscle. Beneath the epimysium, an additional layer of connective tissue, called perimysium, surrounds and groups together subunits of skeletal muscle called fasciculi.

Each fascicle is a bundle of skeletal muscle cells, or myocytes, which are often called skeletal muscle fibers due to their size and cylindrical appearance. Between the muscle fibers is an additional layer of connective tissue called endomysium.

The muscle fiber membrane is called the sarcolemma. Each muscle fiber is made up of multiple rod-like chains called myofibrils, which extend across the length of the muscle fiber and contract. Myofibrils contain subunits called sarcomeres, which are made up of actin and myosin in thin and thick filaments, respectively.

Actin contains myosin-binding sites that allow thin and thick filaments to connect, forming cross bridges. For a muscle to contract, accessory proteins that cover myosin-binding sites on thin filaments must be displaced to enable the formation of cross bridges. During muscle contraction, cross bridges are repeatedly broken and formed at binding sites further along the actin.

Skeletal muscles, striated tissues under the voluntary control of the somatic nervous system, are attached to bones through collagenous fibers called tendons. They are enclosed in a connective tissue called epimysium, which distinguishes the muscle from surrounding structures.

Within each skeletal muscle, like the biceps brachii, are numerous cell bundles, called fascicles, that are also surrounded by connective fascia, perimysium. Each fascicle contains multiple muscle cells, which are individually-enclosed in a plasma membrane known as the sarcolemma. A single muscle cell can be further broken down into myofibrils, filaments composed of actin and mysosin, the functional unit referred to as the sarcomere.

Skeletal Muscle – Voluntary muscle tissue attached to bones, responsible for body movement. Tendon – Tough connective tissue that connects skeletal muscle to bone for force transmission. Sarcomere – Basic contractile unit of muscle fiber composed of actin and myosin filaments. Myofibril – Long, rod-like structure in muscle fibers made of repeating sarcomere units. Epimysium – Outer connective tissue layer that surrounds and protects entire skeletal muscles.

Define skeletal muscle – Explain what skeletal muscle is and its primary function in producing voluntary movement. (e.g., movement) Contrast actin vs myosin – Identify the structural and functional differences between the two key contractile proteins. (e.g., proteins) Explore connective layers – Describe the organization and role of epimysium, perimysium, and endomysium in muscle tissue. (e.g., tissue) Explain Mechanism or Process – Detail how actin-myosin cross bridges form, cycle, and break during muscle contraction and relaxation. Apply in Context – Connect skeletal muscle structure to how it enables movement of bones in voluntary motor actions. (e.g., flexion)

Questions This Skeletal Muscle Video Will Help You Answer: What are the structural layers surrounding skeletal muscle? How do actin and myosin contribute to muscle contraction? What are myofibrils and sarcomeres composed of?

Students – Understand how skeletal muscle structure supports movement and contraction. Educators – Provideds a clear framework in teaching muscle anatomy with clear vocabulary. Researchers – Supports foundational knowledge for studies in muscle physiology and disorders. Science Enthusiasts – Explains the fascinating structure and function of muscles in motion.