1. HISTOLOGY 1.12: MOLECULAR BASIS OF CROSS-STRIATION
AND MUSCLE CONTRACTION
LM micrographs of striated muscle
Low power EM micrograph
High power EM micrograph

2. Structure of the myofibrils
Sarcomer: 2,2-2,5 mm
Myofilaments:
Thick (myosin)
Thin (actin)

3. Myofilaments 1. The thin filament
6-9 nm
F-actin (made up by
several G-actins)
Further proteins involved:

4. Myofilaments 2. The thick filament
Building block: the myosin molecule
L-chains
H-chains
Heads
Arrangement of the myosin molecules within the filament ( molecule/filament)
Bipolar structure
Myosin heads nm

5. The „sliding filament” mechanism of the contraction

6. Cytoskeletal proteins within the sarcomer

7. Triad: T-tubule + two adjacent terminal cisterns of the sarcoplasmic
The sarcoplasmic reticulum and the transverse tubular system (T-system)
Sarcoplasmic reticulum
Longitudinal tubules
Terminal cisterns
triads
Triad: T-tubule + two adjacent
terminal cisterns of the sarcoplasmic
reticulum

8. Summary of the requirements for the
skeletal muscle contraction:
Within the muscle:
1./ Thin and thick filaments (actin and myosin)
2./ Sarcoplasmic reticulum and triad (for the calcium)
3./ Energy source (ATP) and enzyme releasing
the energy (myosin head)
Outside the muscle:
4./ Nerve impulse arriving via the motor endplate
(releasing ACh)

9. Organization of smooth muscle cells
into fiber bundles and their innervation
Contraction of smooth muscle cells