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PSL201 Test 2 Notes 2 - PSL201 Test 2 Notes MUSCLES...

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PSL201 Test 2 NotesMUSCLESStructure of skeletal muscles-Muscle= group of fascicles-Muscle fibres w/in fascicle extend length of muscle from tendon to tendonoTubes with thick (myosin) and thin (actin) filamentsoSurround by mitochondria (ie between the tubes inside the sarcolemmaoMyofibrils each individual tube within the fibreoSarcoplasmic Reticulum (SR)- sac-like membranous network that surrounds the fibreStores calciumoT tubules run perpendicular along the SR-Outside muscle fibreoSarcolemma- plasma membrane on top of SR and T TubulesoNucleioAxon of motor neurons (efferent neurons of somatic nervous system)Release ACh and excitatory-Communication at neuromuscular junctionoAction potential at terminal buttonoVoltage gated calcium channels openoCalcium triggers release of AChoACh diffuses across cleft and binds to nicotinic receptors ion motor end plateoACh triggers opening of channels for small cations sodium and potassiumoNet movement in of positive charge= depolarizationoCauses action potential in muscle cell, spreads through muscle causing contractionoThe ACh that doesn’t get used gets broken down by acetyl cholinesterase into choline and then goes back into theterminal buttonMechanism of force generated in muscle-SarcomereoFound within myofibriloFrom Z line to Z line (Z lines= actin)oM line down the middle surrounded by H zone, then A bandoI band surrounds Z line-Crossbridge cycle componentsoMyosin head undergoes conformational changes, swinging back and forth, like the oar of a boatHigh energy form- high affinity for actinLow energy form- low affinity for actinRelies on ATP hydrolysisoThick myofilamentMyosin molecules twirled around each other, bound at headsEach head has an actin binding site at the top of it and an ATPase binding site on the sideWhere the heads meet along the long twisty thing is called crossbridgesThere is also a bare zone where there are no headsoThin MyofilamentG actin (g for globular proteins) contains a myosin binding siteString together to form F actinTwo strings intertwine to from double helical actinTropomyosin twists around covering all the myosin binding sitesTroponin complexOne binds to actin, one binds to tropomyosin, one has a calcium binding site to move thetropomyosinoCalciumCalcium binds to troponin complex which triggers the movement of tropomyosin which exposes the bindingsite on the actin, crossbridges between myosin and actin, contraction occurs-Crossbridge cycleoPower stroke, myosin head moves propelling thin filament towards centre of muscle (oar propelling boat), thin and thickfilaments detach (oar breaks contact with water), myosin head returns to initial position (oar moved to new position,cycles starts again)
oBinding of myosin to actinADP and P bind to ATPase site on myosin head, head binds to actin monomeroPower StrokeBinding of myosin triggers the release of P and ADP from ATPase site

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Term
Fall
Professor
WOJTOWICZ

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