HISTOLOGY 1.12: MOLECULAR BASIS OF CROSS-STRIATION

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Presentation transcript:

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

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

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

Myofilaments 2. The thick filament Building block: the myosin molecule L-chains H-chains Heads Arrangement of the myosin molecules within the filament (250-350 molecule/filament) Bipolar structure Myosin heads 12- 15 nm

The „sliding filament” mechanism of the contraction

Cytoskeletal proteins within the sarcomer

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

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)

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