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Muscle Tissue: Structure and Function

Learn about the components, histological features, and ultrastructure of skeletal, cardiac, and smooth muscle tissues. Understand the mechanism of muscle contraction and review key concepts.

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Muscle Tissue: Structure and Function

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  1. Muscle Tissue Xing Wenying 邢文英

  2. Introduction • Components: • Muscle cells(muscle fibers) • Elongated, thread-like, containing myofilaments and being contractile • cell membrane → sarcolemma; cytoplasm → sarcoplasm; SER → sarcoplasmic reticulum • CT: contain blood vessels, lymphatics and nerves.

  3. function structure striated striated unstriated • classification : According to the structure and function

  4. Skeletal muscle

  5. Histological features of skeletal muscle fibers • Long cylindrical, 1-40mm long, 10-100um in diameter • Multinucleate, ovoid nuclei, just under the sarcolemma • Cross-striations: alternating dark and light bands

  6. Histological features of skeletal muscle fibers • Dark bands--A bands： Hband, M line Light bands--I bands： Zline

  7. sarcomere: • The sarcomere is the basic contractile unit of striated muscle. It is the segment of a myofibril between two adjacent Z line. • 1 sacromere = 1/2 I band+1 A band+1/2 I band

  8. Myofibrils: Sarcoplasm is filled with long cylindrical filamentous bundles called myofibrils.

  9. Myofibril Sarcoplasmic reticulum Mitochondrium Transverse tubule Ultrastructure of skeletal muscle fibers

  10. myofibrils and myofilaments • Myofibrils are composed of bundles of myofilaments. • Thick filaments and thin filaments.

  11. Thick filaments • 1.5μm long and 10nm in diameter • Occupy A band • Made up of myosin molecules: • --rods: overlap • --heads: cross bridges, • have ATPase activity.

  12. Thin filaments • 1um long, 5nm in diameter • situated in both ending sides of each sarcomere; • Run between and • parallel to thick filaments; • One end attached to the • Z line, the other is free at • H band • composed ofactin, • tropomyosin, troponin

  13. Thin filaments A.Actin: binding site for myosin.

  14. Thin filaments B.Tropomyosin

  15. Thin filaments C. Troponin: is a complex of three sub-units. Tn T(troponin T) Tn C(troponin C) Tn I(troponin I)

  16. Arrangement • I band -- only thin filaments • A band -- both thick and thin filaments • H band -- only thick filaments • Z line -- anchor for thin filaments • M line – fixation of thick filaments

  17. Transverse tubule (T tubule) • Definition: A transverse distributed tubular system formed by Sarcolemma invaginating into sarcoplasm, encircling each myofibrils. • Location: A-I junctional part • Function: Rapidly conduct impulses for contraction to every myofibrils

  18. Sarcolemma with opening to T-tubule T tubule • Transverse tubule (T tubule)

  19. Sarcoplasmic reticulum (SR) • Definition: • A longitudinal distributed tubular • system formed by SER, • encircling each myofibril • between 2 adjacent T tubules. • Terminal cisternae: • Ends of L tubule dilate and fuse • toformflattened sac.

  20. Sarcoplasmic reticulum (SR) • Triad: 1 T tubule + 2 terminal cisternae • Function: • store and release calcium ions • regulating concentration of Ca 2+ • within sarcoplasm

  21. Other organelles and inclusion Mitochondria Glycogen lipid droplet providing the energy necessary for the reactions involved in contraction.

  22. Mechanism of contraction • -- sliding filament hypothesis • The thin filaments slide past the thick filaments and insert further into the A band. • I band and sarcomere become shorter, H band shortens or disappears, whereas A band remains the same length. • Ca2+ and ATP play an important role.

  23. Cardiac muscle • Mainly distributedin the wall of heart; • Has more connective tissue and capillaries; • Some specialized as Purkinje fibers.

  24. Short cylindrical, 80-150um long,10-20um in diameter, with branches, associated with each other; • 1 or 2, ovoid, centrally-located pale-staining nuclei; • Exhibit cross striations, but less distinct; • Microstructure of cardiac muscle

  25. Intercalated disk: unique characteristic

  26. Ultrastructure of cardiac muscle • Myofibril have different diameter, the boundary of myofibril is not very clear. • T tubules are larger, located at Z-line level.

  27. Ultrastructure of cardiac muscle • Sarcoplasmic reticulum is not well-developed, forms less and smaller terminal cisternae, so Diads are common consisting of 1 T tubule and 1 terminal cisternae on one side.

  28. Ultrastructure of cardiac muscle • Intercalated discs • Specialized cell junctions at Z lines.

  29. Ultrastructure of cardiac muscle • rich in mitochondria, glycogen,pigment.

  30. Smooth muscle Seen in blood vessels and hollow viscera, arranged in layers.

  31. Structure ofSmooth Muscle fiber

  32. Mechanism of contraction -- sliding filament hypothesis Summary • The structure of skeletal muscle. • The structure of cardiac muscle. • The structure of smooth muscle.

  33. Summary • The structure of cardiac muscle.

  34. Summary • The structure of smooth muscle.

  35. Homework • Review the characteristics of skeletal muscle and cardiac muscle. • Prepare for nerve tissue.

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