Skeletal Muscle Structure
Zoom in from a whole muscle down to the sarcomere and learn how muscle fiber types differ in speed and endurance.
From muscle to myofibril
A whole skeletal muscle is wrapped in connective tissue and divided into bundles called fascicles, each containing many individual muscle fibers, and each fiber packed with hundreds of thread-like myofibrils that run its full length.
The layered structure of skeletal muscle
This illustration traces skeletal muscle structure from the whole muscle down through fascicles, individual muscle fibers, and myofibrils.
Whole muscle
A skeletal muscle is a bundle of fascicles wrapped in a connective tissue sheath called the epimysium.
Fascicle
Each fascicle is a bundle of individual muscle fibers wrapped in a layer called the perimysium.
Muscle fiber
A muscle fiber is a single, long muscle cell containing many nuclei and hundreds of myofibrils.
Myofibril
Myofibrils are thread-like structures made of repeating sarcomeres, the basic contractile unit of muscle.
Muscle fiber types
Skeletal muscle fibers come in different types: slow-twitch fibers resist fatigue and support endurance activity, while fast-twitch fibers contract quickly and powerfully but tire more rapidly.
Structure enables the mechanism
Every level of skeletal muscle's structure, from the whole muscle down to the sarcomere, exists to support the sliding filament mechanism covered in the previous lesson.
Structure completes the story started in lesson one.
From the whole muscle down to the sarcomere, every level of skeletal muscle structure exists to support the sliding filament mechanism that lets muscles generate force.