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Muscles – Part 2

Microscopic Anatomy of Skeletal Muscle. Muscles – Part 2. Anatomy of Skeletal Muscle. Sarcolemma – The plasma membrane around muscle cells . Anatomy of Skeletal Muscle. Myofibrils – Long ribbon-like contractile organelles found in the cytoplasm of muscle cells

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Muscles – Part 2

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  1. Microscopic Anatomy of Skeletal Muscle Muscles – Part 2

  2. Anatomy of Skeletal Muscle • Sarcolemma – The plasma membrane around muscle cells

  3. Anatomy of Skeletal Muscle • Myofibrils – Long ribbon-like contractile organelles found in the cytoplasm of muscle cells • Composed of bundles of myofilaments • Contain light (I) and dark (A) bands along the length of the perfectly aligned myofibrils. • Gives the muscle cell as a whole its striped or striated appearance.

  4. Light I and Dark A Bands Contain the Following: • The Light I Band has a midline interruption, a darker area called the Z discs. • The Dark A Band has a lighter central area called the H zone.

  5. Sarcomeres • Sarcomeres – Tiny contractile units • Myofibrils are actually chains of sarcomeres. • Sarcomeres are aligned end-to-end like boxcars in a train.

  6. Myofilaments • Myofilaments – Filaments (threadlike protein) composing the myofibrils. • 2 Types: • Thick Filaments (Myosin Filaments) • Thin Filaments (Actin Filaments)

  7. Thick Filaments • Thick Filaments (Myosin Filaments) – Made mostly of bundled molecules of the protein myosin • Also contain ATPase enzymes, which split ATP to generate the power for muscle contraction. • Extends the entire length of the Dark A Band

  8. Cross Bridges on Myosin Filaments • Notice that the midparts of myosin filaments are smooth, but their ends are studded with small projections, or cross bridges. • Cross Bridges (myosin heads) – Projections found on myosin filaments that link the thick and thin filaments together during contraction.

  9. Thin Filaments • Thin Filaments (Actin Filaments) - Composed of the contractile protein called actin • Are anchored to the Z disc • When contraction occurs, the actin-containing filaments slide toward each other.

  10. Thin Filaments • The light I bands only contains thin filaments. • The thin filaments overlap the ends of the thick filaments but do not extend into the H Zone (bare zone).

  11. Sarcoplasmic Reticulum • Sarcoplasmic Reticulum – A specialized smooth endoplasmic reticulum. • The interconnecting tubules and sacs of the SR surround each and every myofibril. • Similar to a sleeve surrounding your arm • Major Role: Store calcium and to release it “on demand” when the muscle fiber is stimulated to contract.

  12. What Happens During Contraction

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