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Muscular Tissue General description 1) components: ---cell: muscle fiber--myofiber • elongated thread-liked • sarcolemma • sarcoplasm • SER : sarcoplasmic reticulum ---extracellular G.S: CT with BV, LV and N 2) classification According to the structure and function • skeletal muscle: striated voluntary m. • cardiac muscle: striated involuntary m. • smooth muscle: unstriated involuntary m. skeletal muscle cardiac muscle smooth muscle Skeletal muscle Often called Striated or Voluntary Muscle – Has striations that are visible under light microscopy – Under voluntary control – Attached to skeleton ( skeletal) • Characteristics of Skeletal Muscles – Muscle cells are elongated fibers with many peripheral nuclei – Each muscle fiber contains many myofibrils – Each myofibril contains many microfilaments Connective tissue coverings (responsible for force transduction): Epimysium: surround collection of fascicles Perimysium: surround fascicle Endomysium: surround individual fibers epimysium Perimysium Entire muscle Fasciculus of muscle fibres Endomysium A muscle fibre 1) microstructure of skeletal muscle fiber ① long cylindrical 10-100um in diameter,1-40mm long ② multinucleate, nuclei are ovoid, distributed under sarcolemma ③ filled with longitudinal parallel-arranged myofibrils Longitudinal section Transverse section muscle fiber myofibril Thin Filaments Thick Filaments 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 A band I band H-band Z-line M-line --A band (except H band): Thin Filaments Thick Filaments • H band: only Thick Filaments --I band: only Thin Filaments sacromere sacromere:1/2 I band, A band ,1/2 I band the smallest structural and functional unit of myofibril 2) Ultrastructure of myofiber myofibril: ---thick myofilament: • composed of myosin: ---thin myofilament: • Compose of • A. actin • B. tropomyosin • C. troponin: Transverse tubule (T tubule): ---definition: sarcolemma and basement membrane invaginate into sarcoplasm to form a transverse distributed tubular system ---location: A-I junctional part ---function: transfer the information into cytoplasm ③ Sarcoplasmic reticulum: ---definition: A longitudinal distributed tubular system formed by smooth endoplasmic reticulum Sarcoplasmic reticulum ---structure: H-A band: longitudinal enclose myofibril-- longitudinal tubule A-I junction: enlarge to form flattened sac —terminal cisternae •triad: one T-tubule + two terminal cisternae triad ---function: there are calcium pump proteins (ATPase) on membrane, so it can store and release calcium ions Cardiac muscle 1) Microstructure of cardiac muscle • ① short column in shaped, 100um long,15um in diameter, with branches, the branches associated with each other to form a network • ② 1-2 ovoid nuclei, centrally-located • ③ striated, but no very clear • ④ intercalated disc: junctional part • LM: dark striation across the cardiac fibers Cardiac muscle Cardiac muscle: show intercalated disc 2) Ultrastructure of cardiac muscle similar to skeletal muscle, composed of thick, thin filament and have sarcomere ① myofibril have different diameter, the boundary of myofibril is not very clear ② transverse tubule are thicker, located at Z-line level (skeletal muscle : A-I junctional part) diad cardiac muscle ③ sarcoplasmic reticulum is not well-developed, form less terminal cisternae ④diad: one T-tubule + one terminal cisternae (skeletal muscle : triad) triad skeletal muscle ④ intercalated discs transverse portion : connection -intermediate junction -desmosome longitudinal portion: communication -gap junction transverse portion longitudinal portion Smooth muscle 1) microstructure of smooth muscle ① elongated, spindle-shaped cells, 8um in diameter, 200( 20-500)um long ② rob-liked or ovoid nucleus ③ no striation, no myofibril 2) ultrastructure of smooth muscle ① caveola on sarcolemme invaginate into cytoplasm ② dense patch: under sarcolemma dense body: in sarcoplasm ③ intermediate filament: caveola dense body dense pach smooth muscle under SEM Compare with three muscle tissues • 1. The location of T tubules of cardiac muscle differ from those of skeletal muscle, the former lie at the • A. A-I junctions B.I bands • C. A bands D.M lines √• E. Z lines • 2. Sarcoplasmic reticulum of muscle fiber is composed of • A. lysosome B. mitochondria • C. microsome D. RER √• E. SER 3.The cell junction which transmit rapidly an electrical impulse between adjacent smooth muscle cells is • A. tight junction B. intermediate junction D. desmosome √• C. gap junction • E. semidesmosome • Questions: • Describe the characteristics of muscle tissue. • Compare the similar with the difference for three kinds of muscle cells according to their fine structure and ultrastructure.
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