[Flash] Cơ - Muscle - eduMedia

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Summary

This animation presents the structure and the ultrastructure of skeletal muscle in order to help better understand muscle contraction

Learning goals

To learn the anatomical organization of skeletal muscle.
To understand muscle contraction at the scales of both the sarcomere and the whole muscle.
To understand the relationship between sarcomere structure and function.
To bring out the relationship between the shrinking of the I bands and the sliding of the myofilaments.

Learn more

The skeletal muscles make up part of the locomotive system. Attached to the bones of the skeleton by tendons, the skeletal muscles display singular physiological properties: excitability and contractility.
A skeletal muscle is made up of bundles. Each bundle is composed of an assembly of elongated muscle cells called muscle fibers. The muscle, bundles and fibers are surrounded by an envelope of connective tissue.
A muscle is an organ whose functioning is controlled by the nervous system. A muscle requires nutrients and oxygen (O2) delivered by the blood in order to function. A muscle is therefore well supplied with both nerve connections and vascular tissue.
A muscle fiber results from the fusion of many undifferentiated cells called myoblasts. The muscle fiber is thus a multinucleated cell. Viewed under an optical microscope, a muscle fiber displays a transverse striation. This striation results from the alternation of dark and light bands. The light bands are called I Bands, and the dark bands are referred to as A Bands.
A muscle fiber contains, in its cytoplasm (called “sarcoplasm”) structures known as myofibrils. These are thin filaments of the protein actin and thick filaments of the protein myosin. The myofibrils correspond to a succession of sarcomeres, where each sarcomere is united with the adjacent sarcomere at a Z band.
When muscle tissue contracts, one observes a shrinking of the light bands, while the dark bands remain globally the same size. The sarcomeres shorten during the muscle’s contraction, creating a shortening of the muscle fibers , then a shortening of the entire muscle. This phenomenon permits, for example, the connection of segments of members (upper arm/forearm/hand).

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