Skeletal Muscle and Muscle contraction
Terms
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- Muscular Tissue
-
organized single direction contraction
MYOCYTE=Muscle Fiber =Myofiber
-acidophilic due to microfilaments - Organization
-
-Epimysium: each muscle covered by dense irregular CT/fascia
-Perimysium: covers ind. muscle fasicles
-Endomysium: each cell surrounded by CT - Light Microscopic structure
-
-elongated cell with peripheral multiple nuclei
-contian many myofibrils
-myofibrils contain many thick and thin myofilaments
-I band=isotropic does not change plane of light so light in color, only thin myofilaments
-A band=anisotopic changes plane of light, dark colored, thick and thin filaments overlap
in btw myofibrils are mitochondria and glycogen
nucleus on periphery due to myofibrils filling up the cell
adv to longer fibers is more force of contraction more rapid single nerve can innervate many fibers (motor unit) - ELectron microscopic
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T-tubule system of skeletal muscle:
invaginations from sarcolemma at level of A-I bands
encircle myofibrils
Conducting system (muscle triad)
-Sarcoplasmic reticulum (sER) network surrounds individual myofibrils
-sarcoplasmic reticulum dilate to form terminal cisterae at A-I band level
-One t-tubule and two terminal cisternae form a triad
-take wave of depolarization from nerve on surface inside cell - cont'd
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conduction system (motor end plate)
-nerve axon-muscle cell contact
Myofibrils
-muscle cells contain myofibrils composed of myfilaments
-thick myosin2
-thin actin tropomyosin and troponin
-binding proteins actinins and tinin at z-line and m-line proteins
-nebulin regulates assembly and length of actin, desmin links adjacent myofilaments, spectrin and dystrophin connect myofilaments to cell surface - Thick and Thin myofilaments
-
Thick
-2 heavy chains
-4 light chains associated with globular heads
-globular head have binding site for actin and Atp
Thin
-double helix of f-actin having myosin binding sites
-tropomyosin located in groove covering binding sites
-troponin binds actin thus preventing myosin from binding
-increased calcium moves troponin and tropomyosin allowing binding - Banding
-
A
thick overlapping with thin
I
thin myofilaments
H
w/o thin
M
thick connected contains creatinine kinase enzyme for atp maintenance
Z
thin of adjacent sarcomeres anchored
alpha-actinin, myosin2 attach to z line by spring like protein, tinin - classification
- see table in notes
- myogenesis
-
hypertrophy
by satellite cell division
individual myocytes do not divide
atrophy
loss of nuclei and myofibrils
regeneration
small repair done by satellite cells by fusion with existion myocytes and forming new myocytes
large repair by replacing with CT scar - satellite cells
-
stem cells sit with them
-spindle shaped
-heterochromatic, single nucleus
-inactive myoblast in adult
-immature muscle cell