EXAM 3 REVIEW SHEET: MUSCULAR SYSTEM1. Endomysium: delicate CT membrane that surrounds each muscle fiber2. Perimysium: coarse CT membrane that surrounds each fascicle3. Epimysium: tough CT membrane that surrounds group of fascicles 4. Fascicle: bundle of endomysium-covered muscle fibers wrapped in perimysium 5. Tendon: cord of dense fibrous tissue attaching muscle to bone6. Sarcolemma: plasma membrane of muscle fiber7. Sarcoplasm: cytoplasm of muscle iber8. Sarcoplasmic reticulum (SR): specialized smooth ER; stores/releases calciuminto sarcoplsam9. Myoglobin: red pigment that bings and stores oxygen10. Sarcomere: structural unit of skeletal muscle; smallest contractile unit in skeletal muscle a. Distance between 2 successive Z linesb. Contains A band, M line, thin filaments, Z lines, H zone, I bands11. A band: thick filament12. Z line: anchors thin filaments13. H zone: middle region of A band not overlapping with thin filaments 14. I band: regions of thin filaments not overlapping with A band 15. Triad: transverse tubule between 2 terminal cisternaea. Releases calcium ions into sarcoplasm when sarcolemma depolarizes 16. Motor unit: motor neuron and all the skeletal muscle fibers it innervates via axonal termnals 17. NEUROMUSCULAR JUNCTION: junction between axonal terminal of motor neuron and skeletal muscle fiber, separated by neuromuscular clefta. Only 1 neuromuscular junction per muscle fiberb. Motor end plate: highly folded region of sarcolemma of muscle fiber atneuromuscular junctioni. Has highest number of acetylcholine receptors18. PROTEINS IN THIN FILAMENT: a. Actin: contains binding sites for myosin headsb. Tropomyosin: rod-shaped regulatory protein that spirals around actinand blocks myosin binding sites on actin in relaxed skeletal musclec. Troponin: 3 polypeptide complexi. TnC: binds calcium ionsii. TnT: binds to tropomyosiniii. TnI: inhibitory subunit that binds to actin19. ACTIVATION OF MYOSIN HEADS: a. ATPase splits ATP into ADP + Pi (inorganic phosphate), still attached to myosin globular heads activated 20. SKELETAL MUSLCE CONTRACTION: (E-C Coupling)a. Motor neuron activatedb. Axon of motor neuron generates/transmits action potential to axon terminalsc. ACh released from vesicles in axon terminals into neuromuscular cleftd. ACh binds to receptors on motor end plate depolarization generation of action potential at motor end platee. Action potential spreads across sarcolemma and into T-tubules of triadsf. Calcium ions released from terminal cisternae of triads into sarcoplasmg. Calcium ions bind to TnC conformational change + removal of tropomyosin from blocking myosin-binding sites on actin h. Myosin heads activated – attached by ADP + Pii. Activated myosin heads = cross bridges; bind to myosin-binding sites on actinj. ADP + Pi dissociate from cross bridges POWERSTROKEi. Attached cross bridges change orientation from right angle to bent position sliding of thin filaments skeletal muscle contraction21. ROLE OF ATP IN MUSCLE CONTRACTION: a. ATP hydrolyzed by ATPase to produce ADP and Pi activates myosinheadsb. ATP required for crossbridge detachmentc. ATP required for sequestration (confiscation) of calcium ions back into SR for storage (active transport)22. Rigor mortis: lack of new ATP skeletal muscle contracturea. Occurs when person dies + ATP synthesis stops actin and myosin are cross linked and skeletal muscles remain contracted23. Muscle fatigue: physiological inability of stimulated skeletal muscle to contract b/c of ATP deficita. ATP production < ATP demand24. SLIDING FILAMENT MECHANISM: sliding of thin filaments past A bands results in muscle contraction a. Structures that shorten when skeletal muscles contract:i. H zoneii. I bandsiii. Sarcomere lengthiv. Skeletal muscle b. Structures that remain the same when skeletal muscles contract:i. A bandsii. Thin filaments 25. FACTORS THAT AFFECT STRENGTH OF SKELETAL CONTRACTION: a. Size of motor units activatedi. Larger motor units = more forceb. Number of motor units activatedi. Force increases as # of motor units activated increasesii. Smaller motor units activated first c. Frequency of skeletal muscle activationi. Force increases as rate of stimulation by motor neurons increasesd. Length of sarcomeres prior to contractioni. Sarcomeres at optimum length = maximum force1. Optimum length: slight overlap b/w A bands and thin filaments with H zoneii. Shortened sarcomeres = decreased force1. Shortened: complete overlap b/w A bands and thin filaments but there is NO H zone2. Zero force generated b/c no H zone to slide intoiii. Stretched sarcomeres = decreased force 1. Stretched: no overlap b/w A bands and thin ilaments 26. 3 TYPES OF SKELETAL MUSCLE FIBERS: a. Slow Oxidative Fibers: slow hydrolyzation of ATP; aerobic respirationi. Highest content of myoglobin (binds/releases oxygen)ii. AKA “RED FIBERS” b/c high content of red myoglobiniii. Predominant in muscles involved in endurance activities (postural muscles)iv. Suited for far endurance events – running marathonb. Fast Oxidative Fibers: fast hydrolyzaton of ATP; aerobic respirationc. Fast Glycolytic Fibers: fast hydrolyzation of ATP; anaerobic respiration using more glycogeni. Lowest myoglobin = appear white = “WHITE FIBERS”ii. Used in activities that are short lived but intenseiii. More in chest and back muscles27. Isotonic contractions: muscle shortens at relatively constant forcea. Force generated by skeletal muscle exceeds weightb. Ex. Lifting weights28. Isometric contractions: force generated by muscle is increasing at constant muscle lengtha. Weight exceeds force generated by muscleb. Ex. Holding box in front of you29. SKELETAL VS. SMOOTH MUSCLE CONTRACTION: a. Smooth muscle requires entry of extracellular calcium into sarcoplasmb. Skeletal muscle does not require entry of extracellular Ca2+30. STRUCTURES PRESENT IN SKELETAL MUSCLE FIBERST THAT ARE ABSENT FROM SMOOTH MUSCLE CELLS:a. Smooth muscle cells lack striations; thin and thick filaments arranged diagonallyb. Smooth muscle lacks sarcomeresc. Thin filaments in smooth muscle lack troponin; calcium binds to CALMODULINd. Smooth muscle cells lacks Z linese. Smooth muscle cells contain DENSE BODIES to anchor thin filamentsf. Smooth muscle cells contain INTERMEDIATE FILAMENTS that resist tensioni. Not in skeletal muscle fibersg. Sarcolemma of smooth muscle cells lacks T-tubules;
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