How it works
Label the structures of a skeletal muscle fiber and the muscle around it, zooming in four steps: the whole muscle, a cut across it, one fascicle, and one fiber drawn out. It covers the homework: label the structures found within a skeletal muscle.
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Three wraps
The epimysium wraps the whole muscle. Inside, the perimysium wraps each fascicle, a bundle of fibers. The endomysium wraps each single muscle fiber. All three run into the tendon that joins the muscle to bone.
Inside a fiber
A muscle fiber is one long cell with many nuclei under its membrane, the sarcolemma. It is packed with myofibrils, and each myofibril is a chain of sarcomeres, the units that shorten when the muscle contracts.
- Epi is upon, peri is around, endo is within: the three wraps go from the whole muscle inward.
Questions and answers
What is the difference between the epimysium, perimysium and endomysium?
They are the three connective tissue layers. The epimysium surrounds the whole muscle, the perimysium surrounds each fascicle, and the endomysium surrounds each muscle fiber.
What is a fascicle?
A bundle of muscle fibers inside a muscle, wrapped in perimysium. A muscle is made of many fascicles.
What is the difference between a muscle fiber and a myofibril?
A muscle fiber is a whole muscle cell. Myofibrils are the long rods of contractile proteins packed inside it, each made of repeating sarcomeres.