Nerve fibers capillaries are found in the endomysium

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nerve fibers & capillaries are found in the endomysium between individual cells (see illustration Seeley 8E, p. 281)
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Fusion of Myoblasts into Muscle Fibers Every mature muscle cell developed from 100 myoblasts that fuse together in the fetus. (multinucleated) Mature muscle cells can not divide Muscle growth is a result of cellular enlargement & not cell division Satellite cells retain the ability to regenerate new cells.
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Muscle Fiber or Myofibers Muscle cells are long, cylindrical & multinucleated Sarcolemma - muscle cell membrane Sarcoplasm filled with tiny threads called myofibrils & myoglobin (red-colored, oxygen-binding protein)
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Transverse Tubules T (transverse) tubules are invaginations of the sarcolemma into the center of the cell filled with extracellular fluid carry muscle action potentials down into cell Mitochondria lie in rows throughout the cell near the muscle proteins that use ATP during contraction
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Myofibrils & Myofilaments Muscle fibers are filled with thread like structures called myofibrils separated by SR (sarcoplasmic reticulum) Myofilaments (thick & thin filaments) are the contractile proteins of muscle
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Sarcoplasmic Reticulum (SR ) System of tubular sacs similar to smooth ER in nonmuscle cells Stores Ca 2+ in a relaxed muscle Release of Ca 2+ triggers muscle contraction
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Filaments and the Sarcomere Thick and thin filaments overlap each other in a pattern that creates striations (light I bands and dark A bands) The I band region contains only thin filaments. They are arranged in compartments called sarcomeres, separated by Z discs. In the overlap region, six thin filaments surround each thick filament
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Striations Dark A bands (regions) alternating with lighter I bands (regions) anisotrophic (A) and isotropic (I) stand for the way these regions affect polarized light A band is thick filament region lighter, central H band area contains no thin filaments I band is thin filament region bisected by Z disc protein anchoring thick & thin from one Z disc to the next is a sarcomere (a functional unit) I A I
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Thick & Thin Myofilaments Supporting proteins (M line, titin and Z disc help anchor the thick and thin filaments in place)
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Overlap of Thick & Thin Myofilaments within a Myofibril Dark(A) & light(I) bands visible with an electron microscope
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The Proteins of Muscle Tissue Myofibrils are built of 3 kinds of protein contractile proteins myosin and actin regulatory proteins which turn contraction on & off troponin and tropomyosin structural proteins which provide proper alignment, elasticity and extensibility titin, myomesin, nebulin and dystrophin
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Structure of the Sarcomere
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The Proteins of Muscle - Myosin Thick filaments are composed of myosin each molecule resembles two golf clubs twisted together myosin heads (cross bridges) extend toward the thin filaments Held in place by the M line proteins.
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The Proteins of Muscle - Actin
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