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40 Cards in this Set
- Front
- Back
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What are the features of cardiac muscle cells?
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-smaller cells
-single nucleus -frequently branched |
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What are the features of smooth muscle cells?
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-no striations
-single nucleus -taper at ends |
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What is the structure of skeletal muscle cells?
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-numerous, elongated, parallel fibers (each a single cell)
-multinucleated |
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What 3 connective tissue types are associated with skeletal muscle?
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-Epimysium
-Perimysium -Endomysium Muscles are protected and compartmentalized by these layers. |
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Why is there connective tissue associated with skeletal muscle?
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-Holds fibers together
-transmits tensions to tendons -carries BV and nerves to individual fibers |
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Where is epimysium located?
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Around the anatomical muscle
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Where is perimysium located?
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Around each fascicle
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Where is endomysium located?
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Around each fiber
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What is the external lamina and what is its function?
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=basal lamina + reticular fibers
-equivalent structure/function to epithelial basal lamina -attaches fiber to main CT -acts as scaffold for regeneration |
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Why is muscle highly vascularized?
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B/c of its high O2 and nutrition requirements
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What are the striations visible in myofiber due to?
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Alignment of striated myofibrils
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What is the repeat unit in the myofibril?
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The sarcomere
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How is the sarcomere measured?
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From dense line to dense line!
We have many sarcomeres in our muscles |
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What is the A-band of the sarcomere composed of?
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Mainly myosin
=thick filaments |
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What is the I-band and overlap zone of the sarcomere composed of?
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Mainly actin
=thin filaments |
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What is titin?
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-thick filament from M line to Z line
-template for myofibril development -elastic in I-band -> resting elasticity |
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What is the function of nebulin?
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-extends length of thin filament
-defines length of thin filament |
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What are the features of the Z line?
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-alpha-actinin links thin filaments together
-z discs reverse polarity |
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What is the main feature of the M line?
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links thick filaments together?
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What is the thin filament composed of?
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=actin+regulatory proteins
-tropomyosin and troponin =regulatory proteins -helically organized |
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What are thick filaments composed of?
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-bipolar helical polymers of myosin II
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How is force transmitted to the exterior of a fiber?
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-desmin intermediate filaments encircle myofibrils-link myofibrils together to contract as a unit.
-costameres link peripheral myofibrils to the sarcolemma and hence to the ECM and thus laterally transmit force to the connective tissue-may be important in coordinating shortening of active and inactive fibers |
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Where are the mitochondria located in muscle cells?
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In rings surrounding each I band.
-In slow fibers there are add'l mitochondria in longitudinal arrays b/w myofibrils |
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How is contraction activated in the muscle?
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By Ca2+ release into the sarcoplasm
-membranes play a key role in activating contraction |
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What are T tubules?
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Invaginations of the plasma membrane (sarcolemma)
-carry activation signals |
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What is the sarcoplasmic reticulum?
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=endoplasmic reticulum
-longitudinal tubules -lateral=terminal cisternae |
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What is a triad in a skeletal muscle?
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T tubule + 2 lateral cisternae
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What turns off contraction in the muscle cell?
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Ca2+ pump (ATPase)
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What is E-C coupling?
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=Excitation-contraction coupling
-sarcoplasmic reticulum and tubules are involved -T-tubule brings action potential to the interior |
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How does E-C coupling work?
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-Activated:AP-depolarizes sarcolemma, carried down T-tubule, reaches center of fiber
-structure of dihydropyridine (DHP) receptor in T-tubule membrane changes, opens RYANODINE receptor=ca channel in SR membrane -Ca flows from SR into sarcoplasm -muscle is activated |
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What are the features of relaxed E-C coupling?
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-Ca2+ stored in SR
-Ca2+ release channel closed |
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How does contraction occur?
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=sliding of filaments (slide but DONT shorten)
-thick-thin filament overlap increases -A band constant -I band and H zone shorten |
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How does shortening of the sarcomere occur?
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Thick and thin filaments are of opposite polarity in opposite halves of the sarcomere, so Z lines pull towards each other -> shortening
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How does rigor mortis occur?
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ATP runs out for the crossbridge cycle
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Describe the crossbridge cycle.
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Myosin heads on thick filaments are molecular motors.-hydrolyze ATP, coupled to pulling on actin
-process is cyclic -Myosin alone is a slow enzyme (relaxation)-ATP turnover is slow -ATP turnover activated by binding to actin -coupled to powerstroke->contraction |
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What is contraction regulated by?
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Troponin/tropomyosin
-At low sarcoplasmic [Ca], topomyosin sterically blocks myosin binding sites on actin -on activation, troponin binds Ca causing tropomyosin to move, exposing myosin binding site and initiating crossbridge cycling |
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What is the intercalated disk?
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=mechanical and electrical connection b/w cardiac cells
-transverse and longitudinal components -consists of 3 cell junctions |
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What are the 3 cell junctions present in an intercalated disk?
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-2 mechanical-hold cells together to form a coherent unit. .a Fascia adherens b. desmosomes
-1 electrical=Gap junction-connects cells electrically helping tissue to be excited and contract as a unit |
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What is troponin a key marker of?
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-heart attacks
-heart muscle is damaged as a result of heart attacks-troponin leaks into bloodstream. Increased blood levels indicate myocardial injury -cardiac isoform of troponin is unique -levels stay elevated for at least a weak allowing detection of a heart attack that occurred days earlier |
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What are muscular dystrophies due to?
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-most commonly a mutation in dystrophin
-connects actin cytoskeleton to plasma membrane, then to ECM via a transmembrane glycoprotein complex |
