This document discusses the histology of skeletal muscle. It describes the structure of skeletal muscle fibers, which are long, cylindrical, multinucleated cells. Skeletal muscle fibers contain repeating contractile units called sarcomeres bounded by Z-lines. The document outlines the intracellular structures that facilitate muscle contraction including sarcoplasmic reticulum, T-tubules, and myofibrils containing A-bands and I-bands. Satellite cells, innervation by motor neurons, and the regeneration process of skeletal muscle are also summarized.

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

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

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

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

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)

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

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

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

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

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

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

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