EM 385 Skeletal Muscle

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Skeletal Muscle

Transmission electron microscopy (TEM) of skeletal muscle.

Skeletal muscle cells contain myofibrils composed of longitudinal arrays of sarcomeres composed of alternating light and dark bands (i.e., striated).

I Bands (tan) - lighter bands with a dark line at its center
- Parallel arrays of thin (actin) filaments
- Narrows with contraction
Z Lines (purple) - dark lines at the center of I bands
- One end of the thin filaments anchor to Z lines
A Bands (brown) - darker bands with a lighter line at its center
- Parallel arrays of thick (myosin) filaments
- Point in opposite directions from M lines
H Band (yellow) - lighter bands at the center of A bands
M Line (red) - darker lines at the center of H bands
- One end of the thick filaments anchor to M Lines

The openings of the T-tubules can be seen at the junction of the A-and I-bands.

The narrow bands of cytoplasm contain mitochondria (red), sarcoplasmic reticulum (cyan), and glycogen granules (black).

Courtesy of Mary Garry, Department of Medicine, Cardiovascular Division, University of Minnesota Medical School, Minneapolis, MN