SI Summer Session Chapter 9 A&P, Microscopic anatomy - skeletal Muscle
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JustBrumley on May 22, 2012
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Microscopic anatomy - skeletal Muscle
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19 terms
Terms | Definitions |
|---|---|
 Skeletal Muscle Fiber | Cylindrical cell 10 to 100 m in diameter, up to 30 cm long - Muscle cell, muscle fiber Multiple peripheral nuclei Many mitochondria - increased energy demand Glycosomes for glycogen storag Myoglobin for O2 storage - similar to hemoglobin |
| Myofibrils | Densely packed, rod-like elements ~80% of cell volume Organelles squeezed between Exhibit striations: perfectly aligned repeating series of dark A bands and light I bands |
| Sarcomere | Smallest contractile unit (functional unit) of a muscle fiber The region of a myofibril between two successive Z discs Composed of thick and thin myofilaments made of contractile proteins |
| Thick filaments of the Sacomere | Run the entire length of an A band Composed of the protein myosin |
| Thin filaments of the Sacomere | Run the length of the I band and partway into the A band Twisted double strand of fibrous protein F actin |
| Z disc of the Sacomere | Coin-shaped sheet of proteins that anchors the thin filaments and connects myofibrils to one another |
| H zone of the Sacomere | Lighter mid-region where filaments do not overlap |
| M line of the Sacomere | Line of protein myomesin that holds adjacent thick filaments together |
| Myosin tails of the Thick Filament | 2 interwoven, heavy polypeptide chains |
| Myosin heads of the thick filament | 2 smaller, light polypeptide chains that act as crossbridges during contraction Binding sites for actin ofthin filaments Binding sites for ATP ATPase enzymes |
| Elastic filament (Titin) (Protein of the Sarcomere) | Extends throughout thick filament Anchors thick filament to Z disc and M line |
| Dystrophin (Protein of the Sarcomere) | Connects thin filaments to sarcolemma Mutated in muscular dystrophy (MD) |
| F (fibrous) actin | Consists of G (globular) actin subunits In Thin filament of the sacromere |
| G actin | Bears active sitesfor myosin head attachment during contraction In Thin filament of the sacromere |
| Tropomyosin | Stabilizesactin and blocks myosin binding In Thin filament of the sacromere |
| Sarcoplasmic Reticulum (SR) | Network of smooth endoplasmic reticulum surrounding each myofibril Pairs of terminal cisternae form perpendicular cross channels Functions in the regulation of intracellular Ca2+ levels |
| T Tubules | Continuous with the sarcolemma Penetrate the cell's interior at each A band-I band junction Associate with the paired terminal cisternae to form triads that encircle each sarcomere conduct impulses deep into muscle fiber |
| T tubule proteins | voltage sensors |
| SR foot proteins | gated channels that regulate Ca2+ release from the SR cisternae |
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