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31 Cards in this Set
- Front
- Back
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What are the single-cell contractile units?
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Myoepithelial cells - important in secretory glands where they fucntion to expel secretions from glandular acini
Pericytes - smooth muscle-like cells that surround blood vessels Myofibroblasts - role in wound contraction and secretion of collagen |
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Where are the visceral striated and unstriated muscles found?
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striated:
-tonuge, pharynx, lumbar part of diaphragm, upper part of esophagus nonstriated (smooth): -viscera, vascular system, arrector pili mm of skin, instrinsic mm of eye |
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What are some embryogenic features of skeletal mm?
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precursor of myoblasts
form multinucleated cells called myotubes satellite cells - stem cells found in mature muscle |
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What are the three connective tissue sheaths?
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Endomysium:
-reticular fibers surrounding each muscle fiber Perimysium: -fibrous CT that surround group of muscle fibers called bundle or fascicle Epimysium: -dense irregular CT that surrounded entire mm. Vascular supply and nerve penetrates epimysium |
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What are the different filaments in skeletal mm?
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Myofibrils:
-cylindrical, extend entire length of cell -arranged bundles of thick and thin filaments Myofilaments: -composed of actin and myosin, each remains CONSTANT length regardless of state of contraction Thin filaments: F-Actin -polymer of G actin monomers arranged in double helix; each monomer has active site that binds to myosin Tropomysin - binds head-to-tail; located in grooves of F-actin helix troponin - TnT = tail, binds troponin complex to tropomyosin; TnI = binds to actin and inhibits interaction of actin and myosin; TnC = binding site for calcium Thick filaments: myosin II - two heavy and two light chains; globular head has two specific binding sites for actin and ATP |
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What is are the parts of the structure of skeletal muscle fibers?
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myofibrils held together by intermediate filaments called desmin
A band: -dark (birefringent) -actin and myosin (6 thin around 1 thick) H band - center of A band where there is NO actin M line - center of H band, cross-connection between myosin filaments I band: -light (monorefringent) -actin only -nebulin assists binding to Z disk as well as regulates length of thin filament Z-line: -has alpha-actinin, located at center of I band -anchored to each other by desmin -peripherally located Z disks anchored to sarcolemma by vinculin |
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What are the accessory proteins?
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Nebulin:
-helps alpha actinin anchor thin filaments to Z lines -regulates length of thin filaments Tropomodulin: -attaches to free portion of thin filament, called actin-capping protein because doesn't allow actin molecules to fuse together Desmin: -intermediate filament around Z lines, attaching them to one another and plasma membrane Titin: -anchors thick filaments in Z lines -prevents excessive stretching of sarcomere C protein: -binds to thick filaments near M line Myomesin: -protein at M line that cross-link adjacent thick filaments |
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What is a sarcomere and the SR?
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Sarcomere:
-extends from Z line to Z line -shortens during muscle contraction SR: -surrounds myofilaments and forms meshwork around each myofibril -forms pair of dilated terminal cisternae and encircle myofibrils at junction of each A and I band -regulates muscle contraction by controlling calcium |
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What are Triads?
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contain one T tubule and 2 terminal cisterns
T tubles = invaginations of sarcolemma at junction of A and I band Terminal cisterns = expansions of SR, release calcium to initiate contraction 2 triads in each sarcomere |
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What is the Sliding filament model?
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During contraction, thick and thin filaments do not shorten but increase their overlap
Thin filaments slide past thick filaments and penetrate deep into A band, which remain CONSTANT in length I bands and H bands shorten as Z disks draw closer to each other |
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What happens at the NMJ?
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synaptic vesicles contain ACh
Motor end plate is a part of the sarcolemma that contains ACh receptors and helps for the NMJ Ca in axon terminal causes axonal vesicles to fuse with axonal membrane Binding of ACh to receptor starts AP ACh is quickly destroyed by AChesterase |
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How is a muscle contraction initiated?
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Sarcolemma is depolarized at NMJ
Dihydroxypyridine (DHP) is a voltage sensor receptor on T tubules that alters its conformation as a function of membrane depolarization RYR (Ryanodine) channel is a Ca release channel present on wall of SR for Ca movement Conformational change in DHP removes plug from RYR and allows passive flow of Ca into muscle cell cytoplasm. Ca release trigger binding of actin and myosin, leading to muscle contraction |
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How is actin activated by Ca?
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Troponin I is bound to actin and hinders myosin-actin interaction at rest
Ca binding by troponin C results in conformational change that breaks TnI-actin bond; tropomyosin shifts its position slightly and uncovers myosin-binding sites Relaxation happens when Ca conc. in cytosol is reducts that Tn C loses its bound Ca |
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What is Excitation-contraction coupling?
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ATP hydrolyzed when thin and thick filaments slide over each other (heads of cross bridges pivot)
when cross-bridges break a new molecule of ATP binds to myosin head so that a new cycle can begin ATP consumed in process of Ca uptake |
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What are Type I fibers?
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small fibers
also called Slow Oxidative fibers appear Red many mitochondria and large amounts of myoglobin and cytochrome complexes high levels of mitochondria demonstrated by succinic dehydrogenase and NADH-TR staining slow twitch, fatigue-RESISTANCE motor units Myosin ATPase reaction velocity is slowest EG. limb muscles and long muscles of back -muscles of high-endurance athletes such as marathon runners |
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What are Type IIA fibers?
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intermediate fibers
Fast oxidative glycolytic fibers many mitochondria and high myoglobin content anaerobic glycolysis --> high amounts of glycogen fast-twitch, fatigue RESISTANCE motor units with high peak muscle tension Eg. sprinters, middle-distance swimmers and hockey players |
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What are Type IIB fibers?
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fast glycolytic fibers
Large fibers, appear white less myoglobin and mitochondria low oxidative but high anaerobic Fast twitch, fatigue PRONE motor units and generate high peak muscle tension Myosin ATPase velocity is fastest rapid contractions and fine movements Eg. Extraocular muscles, short distance sprinters, weight lifters, field athletes |
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What are some of the staining classifications of skeletal muscle?
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On basis of color (oxidative enzyme activity NADH-TR reactions in fresh tissue)
-Red (appear dark blue) -White (appear light blue) -Intermediate Speed of contraction and metabolic activity (cytochrome oxidase) -Red (appear lighter) -White (appear darker) -Intermediate |
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What are Caveolae?
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numerous invaginations of the plasma membrane, involved in calcium uptake and release
equivalent to T-tubles in striated muscle, found in smooth muscle |
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What are the intermediate filaments in smooth muscle cells?
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Desmin (skeletin):
-major protein of intermediate filaments in all smooth mm. Vimentin: -additional component of vascular smooth mm. Dense bodies: -one is membrane associated, one is cytoplasmic -both contain alpha actinin thus similar to Z line of striated mm. both thin and intermediate filaments attach to dense bodies and transmit contractile force adjacent to smooth mm. cells and reticular fibers |
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What are the two main types of smooth muscles?
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1. Visceral (single-unit smooth mm.)
-coupled to each other via gap junctions -contract rhythmically as a unit and often exhibit spontaneous action potentials 2. Multi-unit smooth mm. -present in sphincter pupillae of eye, vas deferents, and arrector pili mm. of skin -rare gap junctions, lack of spontaneous depolarizations -forms motor units |
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How do smooth mm. contract?
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NO troponin complex
Calcium binds with Calmodulin this activates myosin light chain kinase and causes its phosphorylation phosphorylated myosin binds with actin dephosphorylation of myosin produces relaxation No T tubules |
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What are the junctions of Cardiac mm?
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three types of junctions:
Fascia adherens (similar to zonula adherens of epithelia) - anchors thin filaments to sarcolemma Desmosomes - bind each fiber to each other Gap Junctions - provide ionic coupling between fibers |
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How is cardiac mm. contraction different from skeletal?
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Sarcomeres, myofibrils, and myofilaments are the same
T tubules are located at Z line instead of junction of A and I band No triads, Diad with 1 terminal cistern and 1 T tubule gap junctions allow calcium to flow from one fiber to another |
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What is Atrial Natriuretic Factor?
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act on kidney to cause sodium and water loss
opposes action of aldosterone and ADH, which conserve sodium and water in kidney |
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What is Duchenne's Muscular Dystrophy?
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Sex-linked recessive
inability to synthesize dystrophin, an actin-binding protein dystrophin stabilizes the sarcolemma, without it excess calcium penetrates the sarcolemma DMD is characterized by replacement of degenerating skeletal mm by fatty and fibrous CT due to necrosis difficulty in running and rising feet from floor creatine phosphokinase level is elevated |
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What is Myasthenia Gravis?
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antibodies block ACh receptors of NMJ
gradual weakening of skeletal muscle clinical signs include thymic hyperplasia due to increase in T and B lymphocyte production |
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What is Tetany?
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calcium ions in extracellular fluids such as plasma is low making the nervous system more excitable and increasing permability to Na ions, allowing easy initiation of action potentials
characterized by tingling of fingers, toes, and lips also hyperreflexia, carpopedal spasm, laryngospasm |
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What is Tetanus?
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also known as lockjaw
caused by toxin (tetanospasmin) made by bacteria Clostridium tetani |
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What is Rigor Mortis?
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postmortem rigidity appearing as hardening of skeletal mm. due to inability of muscle cells to synthesize ATP
Myosin remains bound to Actin Membrane becomes more permeable to Ca+ ions which promote cross bridge attachment of myosin to actin mm. need ACh or ATP to release from contracted state |
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What is Botulism?
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food poisoning caused by ingestion of Clostridium botulinum toxin which inhibits ACh release at NMJ
marked by muscle paralysis, vomiting, nausea |
