Histology of the skeletal muscle

1. Histology of the skeletal muscle • Jeanne Adiwinata Pawitan • Dept. of Histology FMUI Jeanne A Pawitan

2. Muscle tissue • Striated muscle – characteristic striation – specific arrangement of myofilament (contractile protein in a myofibril) • parallel arrays • interdigitating • skeletal muscle • cardiac muscle • Smooth muscle • Myoepithelial cells –glandular unit in glands • Myofibroblast – wound contraction, tooth eruption Jeanne A Pawitan

3. Unique terms – in muscles • sarcolemma= cell membrane • sarcoplasm= cytoplasm • sarcoplasmic reticulum= smooth surfaced endoplasmic reticulum • sarcosome= mitochondria • muscle fiber= muscle cell Jeanne A Pawitan

4. Skeletal muscle • investments • Epimysium – muscle – irregular dense collagenous connective tissue • Perimysium – fascicles (bundles) - < dense • Endomysium – muscle fiber (cell) - reticular fiber, basal lamina / external lamina • cell • Skeletal muscle fibers – striated – parallel • Satellite cells Jeanne A Pawitan

5. Sel/serat otot rangka • Perkembangan: mioblas – berjajar  uj –uj  menyatu myotube – membentuk miofibril  serat otot rangka • Bentuk: panjang seperti tabung – Ø 10-100μm • Di antara serat: endomisium + kapiler kontinu – paralel otot • Sel/serat otot rangka – tak bercabang -bercorak - berinti banyak (multinucleated) • Inti – berderet - di perifr – tepat di dalam membran sel (sarkolema) • ME: Sarkolema masuk ke dalam T tubule (transverse tubule) Jeanne A Pawitan

6. Sarkoplasma: di dalamnya • Banyak miofibfril Ø-1-2 μm –longitudinal – sepanjang serat otot – tersusun teratur  gambaran lurik pada potongan longitudinal: • Pita A – (anisotropik dengan chy polarisasi  gelap) • Pita I – (isotropik dengan chy polarisasi  terang) • ME: Sarkoplasmik retikulum = retikulum endoplasma halus • Berupa jalinan di sekeliling miofibril • Fungsi: menyimpan Ca intrasel (tu sisterna terminal) • Pada perbatasan pita A-I –melebar  sisterna terminal • membrannya mengandung junctional feet (= voltage gated Ca release channels) – berhubungan dengan T tubule • Sisanya = longitudinal sarcotubule + cabangnya Jeanne A Pawitan

7. T tubule • Invaginasi tubular –transversal – bercabang-anastomosis - saling silang dengan miofibril • Letak: pada satu bidang - perbatasan pita A dan I  ada 2 pada tiap sarkomer • Ke arah ekstra sel terbuka • Berhubungan dengan sarkoplasmik retikulum • Fungsi: fasilitasi konduksi gelombang depol sepanjang sarkolema • T tubule + 2 buah sisterna terminal  triad • fungsi: penyebaran gelombang depol – cepat – dari sarkolema -ke seluruh sel –sp. sisterna terminal Jeanne A Pawitan

8. Miofibril • Pita A (gelap) – pita H – pucat – garis M (M line) • Pita I (terang) – garis Z (Z line, Z disk) –gelap • Sarkomer = daerah miofibril di antara 2 garis Z = unit kontraktil serat otot skelet • Kontraksi: • Pita I memendek • Pita H hilang • Pita A tetap • Garis Z saling mendekat Jeanne A Pawitan

9. Satellite cells • Satellite cells = regenerative cells • Small cell – location: shallow depression – muscle cell’s surface • External lamina – shared with muscle cell → inside external lamina • Nucleus-one - > dense - > coarse Jeanne A Pawitan

10. Myotendinuous junction • Connective tissue–muscle – tendon – continuous • Cells tapered – fluted (deeply folded) • Collagen fibers-tendon – penetrate • Infoldings • Endomysium – continuous – reticular fibers Jeanne A Pawitan

11. Innervation of skeletal muscle • Motor nerve fibers (α motor neurons –axon-myelinated) branching – unmyelinated (Schwann cells +) – terminal dilated - myoneural junction (motor end plate) • Axon terminal • Synaptic cleft • Muscle cell membrane • Sensory nerve fibers • muscle spindles – among muscle cells –stretch Rx • Golgi tendon organ (neurotendinuous spindle)– inhibitory feedback - α motor neurons - relax Jeanne A Pawitan

12. Regeneration of skeletal muscle • Skeletal muscle fiber ≠ mitosis • Satellite cells • Injury: satellite cells mitosis – hyperplasia • Muscle building: satellite cells fused with skeletal muscle fibers  mass increased  hypertrophy Jeanne A Pawitan