Skeletal muscle fibers
Multiple bundle of cells (fascia) joint together called muscle fiber.
Skeletal muscle is voluntary muscle.
Skeletal muscle tissue is attach to skeletal/bone and allow movement.
Skeletal tissue are;
1. Striated muscle or striped muscle
Fibers containing alternating light and dark band.
2. Voluntary
Made to contract or relax by conscious control.
Skeletal muscle tissue Structure and Function
Skeletal muscle composed of hundred or thousand of individual specialized cells called muscle fibers.
Skeletal muscle fibers are skeletal muscle cells.
Muscle fibers contain small fibers called myofibrils, which give cell striated appearance.
Skeletal muscle fiber surrounded by plasma membrane, called sarcolemma, which contains sarcoplasm of muscle cells.
Numerous sarcosomes (mitochondria) packed between myofibrils.
Sarcoplasmic reticulum is very abundant in skeletal muscle cell and closely associated with myofibrils.
Nuclei
Skeletal muscle fibre arises during embryonic development from fusion of 100 or more small mesodermal cells, called myblasts.
Each mature skeletal muscle fiber had 100 or more nuclei.
One fusion occured, muscle fibre loss ability to mitosis.
So number of skeletal muscle fibre is set before born and last life time.
Cell structure and function
1. Sarcolemma
2. Sarcoplasm
3. Nuclei
4. Myofibrils
5. Sarcosome
6. Transverse tubules (T- tubules)
7. Sarcoplasmic reticulum
8. Bands
Myofibrils
Thread like structure
Myofibrils made up of thick and thin filament.
Myofibrils are;
1. Thick myofibrils
Composed of large protein called myosin.
Thick filament diameter 16nm.
Total length of each myosin filament 1600nm.
2. Thin myofibrils
Composed of smaller protein Actin.
Length thin filament 1000nm.
Diameter thin filament 8nm.
Each myofibrils composed 1500 myosin (thick) filament and 300 actin (thin) filaments.
Transverse Tubule (T- tubule)
T-tubule folded back surface of sarcolemma.
Project into muscle fiber and wrap around sarcomere in region where myocin and actin filaments overlap.
Lumen of each T-tubule is filled with extracellular fluid (ECF).
T tubule cross sarcoplasmic reticulum.
T- tubule is to conduct impulse from surface of sarcolemma down into cell.
Sarcoplasmic reticulum
Sarcoplasmic reticulum suspended in sarcoplasm around each myofibrils and running parallel to it.
Sarcoplasmic reticulum contain calcium ion (Ca+).
Sarcoplasmic reticulum membrane actively transport Ca+ ion from sarcoplasm into lumen.
Where Ca+ ion stored in very high concentration.
Main function of SR is to store calcium ions (Ca+).
Band
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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