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Muscular Contraction

Muscular Contraction. Characteristics of Muscles. Muscle fibres are elongated Contraction of muscles is due to the movement of microfilaments All muscles share some terminology: Prefix myo refers to muscle Prefix mys refers to muscle Prefix sarco refers to flesh.

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Muscular Contraction

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  1. Muscular Contraction

  2. Characteristics of Muscles • Muscle fibres are elongated • Contraction of muscles is due to the movement of microfilaments • All muscles share some terminology: • Prefix myo refers to muscle • Prefix mys refers to muscle • Prefix sarco refers to flesh

  3. Skeletal Muscle Characteristics • Most are attached by tendons to bones • Cells are multinucleate • Striated – have visible banding • Voluntary – subject to conscious control • Cells are surrounded and bundled by connective tissue

  4. Connective Tissue Wrappings of Skeletal Muscle • Endomysium = around single muscle fibre • Perimysium = around a fascicle (bundle) of fibres

  5. Connective Tissue Wrappings of Skeletal Muscle • Epimysium = covers the entire skeletal muscle • Fascia = on the outside of the epimysium

  6. Gross Structure of Skeletal Muscle • Skeletal muscles are encased by epimysium: fascia of fibrous connective tissue. • A bundle of cylindrical muscle fibres is surrounded by the perimysium. • Endomysium surrounds each muscle fibre. • Sarcolemmabeneath endomysium is a thin, elastic membrane.

  7. Microscopic Anatomy of Skeletal Muscle • Cells are multinucleate • Nuclei are just beneath the sarcolemma

  8. Microscopic Anatomy of Skeletal Muscle • Sarcolemma – specialized plasma membrane • Sarcoplasmic reticulum – specialized smooth endoplasmic reticulum (network of membranous tubules within the cytoplasm )

  9. Sarcoplasm (cytosol) is the fluid portion in muscle fibres. • Contains contractile proteins, nuclei, mitochondria, sarcoplasmic reticulum.

  10. Microscopic Anatomy of Skeletal Muscle • Myofibril • Bundles of myofilaments • Myofibrils are aligned to give distinct bands • I band = light band • A band = dark band

  11. Muscle Structure • Each myofibril is made up of parallel filaments. • There are 2 kinds of filament called thick & thin filaments. • These 2 filaments are linked at intervals called cross bridges, which stick out from the thick filaments

  12. Microscopic Anatomy of Skeletal Muscle • Sarcomere • Contractile unit of a muscle fibre

  13. Microscopic Anatomy of Skeletal Muscle • Organization of the sarcomere: • Thick filaments = myosin filaments • Composed of the protein myosin • Has ATPase enzymes

  14. Microscopic Anatomy of Skeletal Muscle • Organization of the sarcomere • Thin filaments = actin filaments • Composed of the protein actin

  15. Distinguished area between Z lines. • Thicker filaments confined to A band, a lighter middle region called the H zone. • Thinner filaments arise in middle region of I band, at the Z line. • During contraction, neither thick nor thin filaments change in length. They slide.

  16. Microscopic Anatomy of Skeletal Muscle • Myosin filaments have heads (extensions, or cross bridges) • Myosin and actin overlap

  17. Microscopic Anatomy of Skeletal Muscle • At rest, there is a bare zone that lacks actin filaments • Sarcoplasmic reticulum (SR) – for storage of calcium

  18. Sarcomere H zone A band I band

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