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CHAPTER 4 - MUSCLE TISSUE
Histology Guide
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MICROGRAPH

NAME
EM 390 Sarcomere
TISSUE
Skeletal Muscle
(Drosophila melanogaster)
IMAGE SIZE
9,643 x 6,940 pixels
201 MB
FILE SIZES
17,284 KB (grayscale)
27,690 KB (color)
MAGNIFICATION
Unknown
PIXEL SIZE
0.305
SOURCE
Hans Ris
HVEM Facility
University of Wisconsin
Madison, WI

Don W. Fawcett
Department of Anatomy
Harvard Medical School
Boston, MA

Micrograph is licensed under CC BY-NC-SA 3.0.

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EM 390 Sarcomere

Sarcomere

Transmission electron microscopy (TEM) of the flight muscle of the Drosophila melanogaster.

The bands in flight muscle refer to the sarcomeres, the basic contractile units of muscle fibers. The sliding of actin filaments over myosin filaments shortens the sarcomere, generating the force required for muscle contraction.

  • A Bands - contain the entire length of the myosin (thick) filaments (green) and overlaps with the actin (thin) filaments (blue)
    • Myosin filaments are composed of myosin molecules with a long tail and a globular head
    • Myosin heads (purple) form cross-bridges with actin filaments
      • ATP hydrolysis allows myosin heads to pull actin filaments inward
  • H Bands - light regions in the center of A bands
    • Only myosin filaments are present
    • Narrows during muscle contraction
  • I Bands - contain only actin (thin) filaments (blue)
    • Bisected by the Z line
    • Narrower in insect muscle than in vertebrate muscles
    • Narrows during muscle contraction
  • Z Lines (yellow) - dark regions in the center of I bands
    • Anchors the actin filaments
    • Marks the boundary between adjacent sarcomeres

Tropomyosin and troponin are regulatory proteins associated with actin filaments that control the access of myosin heads to the binding sites on actin filaments.

Courtesy of Hans Ris, HVEM Facility, University of Wisconsin, Madison, WI, and Don W. Fawcett, Department of Anatomy, Harvard Medical School, Boston, MA

© 2005-2026. T. Clark Brelje and Robert L. Sorenson