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19 Cards in this Set
- Front
- Back
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How is skeletal muscle organized?
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Whole muscle
fasicle (bundle of muscle fibers) muscle fiber myofibril myofilament |
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Describe muscle fibers
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-large and multinucleate
-composed of bundles of myofibrils -1000s to 100,000s muscle fibers make up muscle |
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What are t-tubules?
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-a continuation of the sarcolemma that make contact with the terminal cisternae of the SR
-they carry the action potential into the muscle fiber |
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What is the site of calcium storage in a muscle fiber?
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-the sarcoplasmic reticulum (SR)
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What is the process of calcium release from the SR?
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-the membrane depolarization opens the L-type calcium channel
-mechanical coupling between the L-type Calcium channel and the Ca2+-release channel causes the Ca+2 release channel to open - Ca+2 exits the SR via the Ca+2 release channel and activates troponin C -->muscle contraction -the depolarization of the t-tubules causes a conformational change in the DHP receptor that MECHANICALLY opens the RYR on the SR causing calcium to be released from the SR |
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What is Store-operated Ca+2 entry? (SOCE)
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- new concept-transarcolemmal calcium entry
-required to sustain SR Ca+2 stores during repeated contractions -low SR Ca+2 triggers influx of calcium across the sarcolemma -capable of replenishing depleted SR Ca+2 stores -There is a Ca+2 sensor in the SR (stim1) -Ca+2 release activated Ca+2 (CRAC) channel in the t-tubule membrane (responds to Ca+2 levels) |
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What is store-independent Ca+2 entry? (excitation-coupled Ca+2 entry (ECCE))
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-it is activated by repetitive or prolonged depolarization
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What are skeletal muscle myofibrils?
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- they are the building blocks of muscle fibers and are made up of myofilaments
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What are the two types of myofibrils?
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-Thick (myosin) Filaments
-Thin (actin) filaments |
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Describe the thick (myosin) filaments
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-single filament composed of many myosin molecules
-each myosin molecule is composed of two proteins twisted together that forms a tail with two-heads (cross-bridge) -has ATPase activity |
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What are some problems that can occur with the myosin?
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-mutations; hereditary myosin myopathies= muscle weakness
- susceptible to glycation which can alter myosin function |
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What is the thin (actin) filaments composed of?
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-complex of three proteins
1. Actin= globular (G) actin molecules form filamentous (F) actin which is a 2-stranded helical structure 2. Tropomyosin = inhibits the binding of myosin and actin 3. Troponin= Ca+2 sensitive molecular switch |
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What are the three subunits of troponin?
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-TnC= calcium sensor; calcium binding produces a conformational change in Tl
-TnT= links troponin complex to tropomyosin; controls the position of tropomyosin on the thin filament -Tnl= binds to actin and inhibits myosin ATPase |
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What percentage of muscle protein do actin and myosin together account for?
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-50-60%
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How are myofilaments arranged?
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-into contractile units called SARCOMERES
-smallest functional unit that produces force -overlapping of the thick and thin filaments -arrangement stabilized by several additional proteins |
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Describe a sarcomere
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- run from z-disk to z-disk
- I-band= split in middle by z-disk; contain thin filaments, intermediate filamentous proteins -A-band = contains the entire thick filament and some of the overlap of thin filament - M-line= splits the middle of A Band where some of the tails overlap |
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What are the additional proteins that help to stabilize the sarcomere?
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-titan= stabilizes the myosin (thick) filaments in the longitudinal axis; largest known protein; contributes to the strength through stretch
-nebulin= acts as protein ruler that regulates the length of the actin filaments; in the longitudinal axis -Dystrophin= in the transverse axis; links the myofibullar array to the cell membrane |
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What is the proportion of thin filaments to thick filaments?
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6 thin filaments for each thick; to allow for maximum overlap
-hexagonal array |
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What is Muscle Dystrophy?
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- abnormalities in the genes that code for DYSTROPHEN
-syndromes characterized by muscle wasting and muscle weakness |
