14.1 POJA-L6227-B Electron micrograph of the sarcomere structure in myofibres (human)
14.1 POJA-L6227-B Electron micrograph of the sarcomere structure in myofibres (human)
Title: Electron micrograph of the sarcomere structure in myofibres (human)
Description:
- Sarcomere unit (red) running from Z- to Z-line (green Z) and all sarcomeres are aligned parallelly and are well organised in register. The sarcomere is the smallest functional unit and measures between 1.5 – 4 micrometers long depending on type of muscle and on the degree of stretch.
- (yellow) I-band (isotropic) is composed of thin actin filaments.
- (yellow) A-band (anisotropic), the thicker myosin filaments form the A-band of the myofibril.
- (blue) H-band with M-line (green M), the dark centre line within the blue H-zone is the green M-line where cross-linking of the myosin filaments occurs.
Background:
The contraction unit comprises the thin filaments, α-actin and associated proteins, and thick filaments (myosin and associated proteins). The Z-line (or disc) represents a dark line within a lighter I-band (isotropic). The sarcomere unit runs from Z-disc tot Z-disc. In the centre of the sarcomere is a dense A-band (anisotropic) made up of thick filaments, with a lighter H-zone. The M-line (or band) bisects the H-zone (or band).The thin filaments are held together in the Z-disc. The M-band is the interconnection site for the thick filaments.
This figure also illustrates the electron microscopical elements of the sarcomere filaments as well as the position of mitochondria between the sarcomere units (human). The triad system (red arrows), i.e., the cross sections through sarcoplasmic reticulum cisterns that are adjacent to the invading T tubules of the sarcolemma serve for the release and restorage of Ca ions upon neurogenic stimulus.
See also:
- 14.1 POJA-L6162 Electron micrograph of a cross sectioned sarcomere of skeletal muscle fibre
- 14.1 POJA-L6144+6287 Cross section through myofilaments in the A-band of a sarcomere
- 14.1 POJA-L6049+6287 Cross section through myofilaments in the M-band of a sarcomere
Keywords /Mesh: locomotor system, skeletal muscle, striated muscle, myofibril, sarcomere, myosin, actin, A-band, I-band, H-band, M-band, Z-line, myofilament, electron microscopy, POJA collection