HISTOLOGY 1.12: MOLECULAR BASIS OF CROSS-STRIATION HISTOLOGY 1.12: MOLECULAR BASIS OF CROSS-STRIATION AND MUSCLE CONTRACTIONAND MUSCLE CONTRACTION

LM micrographs of striated muscleLM micrographs of striated muscle

Low power EM micrographLow power EM micrograph

High power EM micrographHigh power EM micrograph

Structure of the myofibrils

Myofilaments:

Thick (myosin)

Thin (actin)

Sarcomer: 2,2-2,5 m

Myofilaments 1. The thin filament

F-actin (made up by

several G-actins)

Further proteins involved:

6-9 nm

Arrangement of the myosin molecules within the filament (250-350 molecule/filament)

Bipolar structure

Myofilaments 2. The thick filament

Building block: the myosin molecule

12- 15 nm

Heads

L-chains H-chains

Myosin heads

The „sliding filament” mechanism of the contraction

Cytoskeletal proteins within the sarcomer

The sarcoplasmic reticulum and the transverse tubular system (T-system)

triads

Triad: T-tubule + two adjacent terminal cisterns of the sarcoplasmic reticulum

Sarcoplasmic reticulumLongitudinal tubules

Terminal cisterns