1 Muscular Tissue Jun Zhou ( 周俊 ) School of Medicine, Zhejiang University

2 Overview 1) components: -- cell: muscle fiber-myofiber  elongated thread-liked  Sarcolemma （肌膜）  Sarcoplasm （肌质）  Sarcoplasmic reticulum （肌质网） : SER --extracellular G.S: CT with BV, LV and N

3 2) classification According to the structure and function  skeletal muscle ( 骨骼肌 ): striated, voluntary  cardiac muscle ( 心肌 ): striated, involuntary  smooth muscle ( 平滑肌 ): unstriated, involuntary

4 Skeletal muscle

5  Epimysium （肌外膜） : DCT  Perimysium （肌束膜）  Endomysium （肌内膜）

6 LM: long cylindrical um in diameter, 1-40mm long multinucleate, nuclei are ovoid, distributed under sarcolemma filled with longitudinal parallel- arranged myofibrils

7 Skeletal Muscle  Cells are long multinucleate “ cylinders ”

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9 Identify: Endomysium, Perimysium, myofiber and fascicle Endomysium Perimysium Myofiber Fascicle

10 Endomysium: connective tissue, nutrient capillaries, nerve endings and around each myofiber a basal or external lamina

11 Myofiber

12 Myofibril:  1-2um in diameter  cross striation:  light band -I band  dark band- A band --A band: M-line, H-band --I band: Z-line

13 Definitions Isotropic ( 各向同性 )Anisotropic ( 各向异性 )

14 A band : Anisotropic ( 各向异性 ) I band: Isotropic ( 各向同性 )

15 H Band is light and in the center of the A Band

16 Sacromere （肌节） : 1/2 I +A + 1/2 I the smallest structural and functional unit of myofibril

17 1.Transverse tubule (T tubule): 横小管  definition: sarcolemma invaginate into sarcoplasm to form a transverse distributed tubular system  location: A-I junctional part  function: transfer the information into cytoplasm EM:

18 2.Sarcoplasmic reticulum: 肌质网  smooth endoplasmic reticulum  longitudinal tubule ( L tubule )  terminal cisternae ( 终池 )  Triad ( 三联体 ): one T-tubule +two terminal cisternae  calcium pump proteins  store and release calcium ions

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20 3.Myofibril ( 肌原纤维 )  thick myofilament  thin myofilament

21 Skeletal Muscle  Organizational Hierarchy Muscle is composed of fascicles Fascicle (smallest) is composed of myofibers Myofiber is composed of myofibrils Myofibril is composed of myofilaments

22 Thick myofilament  1.5 um long, 15 nm in diameter  composed of myosin ( 肌球蛋白 ) -rob: in bundles -rob: in bundles -head: cross bridge- binding site (ATPase activity) -head: cross bridge- binding site (ATPase activity)

23 Thin myofilament  1 um long,  5 nm in diameter A. Actin ( 肌动蛋白 )- binding site B. Tropomyosin ( 原肌球蛋白 ) C. Troponin ( 肌原 / 钙蛋白 ) -Tn T: bind to tropomyosin -Tn C: binds to calcium ions -Tn I: inhibit actin-myosin interaction

24 Is cross banding evident at the level of the myofibril?Define a sarcomere. A sarcomere is that portion of the contractile apparatus between and attaching to two Z lines. Myofibril

25 Myofibril The sarcomere is the smallest contractile unit. It consists of a precisely organized array of myofilaments. Thick myofilaments consist of myosin. Myosin is ONLY found in the A Band

26 Myofibril Thin myofilaments consist of Actin, tropomyosin and troponin. Thin myofilaments are found in BOTH the A Band and I Band

27 Myofibril M Line, in the center of the H Band, consists of proteins that hold myosin filaments together.

28 Myofibril Z Line.

29 Micrograph Provided by Ernest Whitter Electron Micrograph of Human Skeletal Muscle Dark granules are glycogen Myofibril

30 Micrograph Provided by Ernest Whitter Electron Micrograph of Human Skeletal Muscle Sarcomere

31 Micrograph Provided by Ernest Whitter Electron Micrograph of Human Skeletal Muscle A Band

32 Micrograph Provided by Ernest Whitter Electron Micrograph of Human Skeletal Muscle I Band Z Line M Line in H Band

33 Sliding filament hypothesis ( 肌丝滑动学说 )

34 Cardiac muscle

35 LM  short column in shaped, 100um long,15um in diameter, with branches  1-2 ovoid nuclei, centrally-located  striated, but no very clear  intercalated disc

36 EM T tubule at Z-line level less terminal cisternae diad ( 二联体 ): one T-tubule + one terminal cisternae Numerous mitochondria

37 intercalated discs

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39 Smooth muscle

40 LM elongated, spindle-shaped cells, 8um in diameter, 200( )um long rob-liked or ovoid nucleus no striation, no myofibril

41 Smooth Muscle Longitudinal Section Cross Section

42 EM caveola: sarcolemme invaginate into cytoplasm dense patch ( 密斑 ): under sarcolemma dense body ( 密体 ): in sarcoplasm intermediate filament: /composed of desmin ( 结蛋白 ) /10nm in diameter /connect between dense body

43 thick filament: myosin, 15 nm thin filament: actin, 5 nm-fixed on dense patch or body  contractile unit ( 肌丝收缩单位 ): several thick filament and thin filament aggregate

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