Skeletal muscle tissue show a pattern of alternating light and dark band.
Band are caused by actin (thin) and myosin (thick) filament.
1. Dark A Band
Overlapping of thick myosin strands and thin actin strands produce Dark A Band.
2. Light I Bands
Thin actin strands appear alone as light I band.
3. Z line or Z disc
Cutting across each I section is dark Z line. Attachment of actin myofilaments. It separates one sarcomere from next.
4. H-Zone
Within center of A Band is some what light narrow H zone which consists only of myosin strands (thick filaments).
5. M line
M line connect adjacent myosin strands and help to hold myosin myofilaments.
M line attach to center of myosin myofilaments.
6. Sarcomere
Actin and myosin filaments are organized in highly ordered units called sarcomeres, which join end to end to form the myofibrils.
Fundamental unit of muscle contraction is sarcomere.
(One Z line to next Z line)
Alternating dark A and light I band give muscle fiber striated appearance.
Striated pattern;
Actin; light band (I band)
Myosin; dark band (A band)
Muscle proteins of skeletal muscles
Specialized protein in muscles cells are building blocks of the structure to moving of muscle.
Major skeletal muscles protein
1. Actin
2. Myosin
3. Titin
Myofibrils are built from 3 kind of proteins.
1. Contractile proteins
Which generate force during contraction.
Actin and myosin
2. Regulatory proteins
Which help switch contraction process on and off.
Troponin and tropomyosin
3. Structural proteins
Which keep thick and thin filament in proper alignment, provide elasticity and extensibility to myofibrils.
Titin, myomesin, nebulin, dystrophin
Actin filament made up;
Actin
Troponin
Tropomyosin molecule
Myosin filament made up;
Myosin molecule
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