EXSC%223:%Week%of%10/17/16%!Notes%from%textbook%Ch%9.2%9.2!A!skeletal!muscle!is!made!up!of!muscle!fibers,!nerves,!blood!vessels,!and!connective!tissues!• Each!skeletal!muscle!is!an!organ!o Tissues!present:!§ Muscle!fibers!§ Blood!vessels!§ Nerve!fibers!§ Connective!tissue!• Nerve!and!blood!supply!o In!general,!1!nerve,!1!artery,!and!1+!veins!serve!each!muscle!§ Exit!or!enter!near!the!central!part!of!the!muscle!and!branch!throughout!o Supplied!with!nerves!because!voluntary!contraction!(unlike!cardiac!and!smooth!muscle)!o Rich!blood!supply!§ Lots!of!energy!needed!for!contraction!§ Needs!continuous!delivery!of!oxygen!and!nutrients!o Veins!remove!the!metabolic!wastes!to!keep!contractions!efficient!• Connective!tissue!sheaths!o Wrap!muscle!fibers!to!protect!them!and!keep!them!intact!o Epimysium!§ Outermost!connective!tissue!§ Dense!irregular!connective!tissue!§ Surrounds!whole!muscle!o Perimysium!§ Connective!tissue!surrounding!fascicles!• Fascicle:!bundle!of!muscle!fibers!§ Dense!irregular!connective!tissue!o Endomysium!§ Wispy!sheath!of!areolar!connective!tissue!§ Surrounds!each!individual!muscle!fiber!o They!are!all!continuous!with!one!another!and!with!the!tendons!(connect!muscle!to!bones)!• Attachments!o Direct/fleshy!attachments!§ Epimysium!(of!the!muscle)!fuses!with!the!periosteum!(of!the!bone)!or!the!perichondrium!(of!cartilage)!o Indirect!attachments!§ Muscle’s!connective!tissue!extend!beyond!the!muscle!(forming!a!tendon)!to!attach!it!to!bone!or!cartilage!§ More!common!because!of!durability!and!small!size!o Tendons!§ Mostly!made!of!tough!collagen!fibers!§ Withstand!abrasion!of!rough!bony!projetions!!Lecture%10/17%notes!A!layer!of!connective!tissue!(CT)!surrounds!and!separates!every!muscle!• Epimysium:!CT!that!surrounds!a!group!of!fascicles!!o Bundles!fascicles!together!o Muscle!is!made!up!of!many!fascicles!o Dense!connective!tissue!o If!a!muscle!attaches!to!a!tendon,!the!epimysium!will!attach!to!it!o If!a!muscle!attaches!to!a!bone,!the!epimysium!will!fuse!with!the!periosteum!• Perimysium:!CT!that!surrounds!a!fascicle!o Runs!length!of!muscle!(like!epimysium)!o Can!attach!to!bone!and!tendons!(like!epimysium)!o Also!bundles!things!together!(like!epimysium)!§ Bundles!muscle!fibers!(cells)!together!o Dense!irregular!connective!tissue!• Endomysium:!Layer!of!connective!tissue!outside!of!sarcolemma!!o Sarcolemma:!membrane!of!a!muscle!fiber!§ Bundles!all!the!organelles!together!§ Functions!like!any!other!cell!plasma!membrane!o Delicate!connective!tissue!o Connects!to!the!perimysium!Connective!tissue!makes!muscle!tough!• More!you!use!a!muscle!=!more!CT!• Slow!cook!BBQ!to!break!down!the!CT!Myofibril!• Organelle!• Location!of!contraction:!sarcomere!o Smallest!functional!unit!of!muscle!o Runs!from!z-disk!(z-line)!to!z-disk!(z-line)!o Made!of!thin!filaments!(actin)!and!thick!filaments!(myosin)!Skeletal!muscle!structure:!striated!muscle!• Highly!organized!positioning!of!actin!and!myosin!and!z-disks!o Results!in!light!bands!(I-band)!and!dark!bands!(A-band)!§ I-band:!isotropic=light!passes!through!§ A-band:!anisotropic=light!doesn’t!pass!through!it!o Thick!filament;!made!of!myosin;!lots!of!protein;!blocks!light!o Thin!filament;!made!of!actin;!less!protein;!lets!light!in!o Myosin!is!not!attached!to!z-disks!by!actin!in!o H!zone!§ Includes!m!line!§ Fixes!thin!filaments!to!center!of!sarcomere!o Actin!is!present!in!A-band!and!I-band!o Myosin!§ Large!protein!§ Dimer!(made!of!two!proteins)!§ Distinct!regions!• Tail!o Part!attached!to!thick!filament!o Associates!with!M-line!o Anchors!myosin!within!thick!filament!• Flexible!hinge!o Allows!myosin!to!exist!in!2!shapes!§ High!energy:!cocked!§ Low!energy:!trigger!pulled!• Heads!o ATP!binding!site!o Actin!binding!site!o Break!down!ATP!into!ADP!+!Pi!o Actin!§ Thin!globular!protein!§ Have!myosin!binding!site!§ Additional!proteins!• Tropomyosin:!covers!actin!molecule!at!binding!site!o Regulatory!protein!• Troponin!complex:!complex!of!3!proteins!o Attaches!actin!and!tropomyosin!molecules!!Textbook%notes%Ch%9.3%9.3!Skeletal!muscle!fibers!contain!calcium-regulated!molecular!motors!• Skeletal!muscle!fiber!o Long,!cylindrical!cell!o Multiple!nuclei!o Sarcolemma=plasma!membrane!o Huge!cell-10x!bigger!than!normal!body!cell!o Sarcoplasm=cytoplasm!of!muscle!cell!o Glycosomes:!granules!of!stored!glycogen!that!provide!glucose!during!muscle!cell!activity!o Myoglobin:!red!pigment!that!stores!oxygen!o !3!specially!developed!organelles:!myofibrils,!sarcoplasmic!reticulum,!T!tubules!• myofibrils!o rodlike!organelles!that!run!parallel!to!the!length!of!the!muscle!fiber!o make!up!80%!of!the!cell’s!volume!o contains!sarcomeres,!which!contain!myofilaments!o striations!§ repeating!series!of!dark!and!light!bands!along!each!myofibril!• dark!A!bands!o H!zone:!lighter!region!in!its!midsection!§ M!line:!dark!line!that!bisects!the!H!zone!• light!I!bands!o Z!disc!(Z!line):!dark!area!that!runs!through!the!I!band!o Sarcomeres!§ Region!of!myofibril!between!two!Z!discs!§ Smallest!contractile!unit!of!a!muscle!fiber!§ Functional!unit!of!skeletal!muscle!§ Contains!an!A!band!in!between!two!I!bands!o Myofilaments!§ Thick!filaments!contain!myosin!• Extend!the!entire!length!of!the!A!band!• Connected!in!the!middle!of!the!sarcomere!at!the!M!line!§ Thin!filaments!contain!actin!• Extends!across!the!I!band!and!partway!into!the!A!band!• Anchored!by!the!Z!discs!o Molecular!composition!of!myofilaments!§ Muscle!contraction!is!dependent!on!the!myofilaments!§ Myosin!• Consists!of!2!heavy!and!4!light!polypeptide!chains!• Has!a!rod-like!tail!attached!by!a!flexible!hinge!to!two!globular!heads!§ Cross!bridge:!when!a!link!is!formed!between!thick!and!thin!filaments!during!contraction!§ Actin!• Contain!active!sites!for!myosin!heads!to!attach!to!during!contraction!• 2!intertwined!actin!filaments!form!backbone!of!thin!filament!• contain!regulatory!proteins!o tropomyosin!§ rod-shaped!protein!that!spirals!about!the!actin!core!§ stiffens!and!stabilizes!actin!§ when!muscle!fiber!is!relaxed:!blocks!myosin-binding!sites!on!the!actin!o troponin!§ globular!3!polypeptide!complex!• TnI:!inhibitory!subunit!that!binds!to!actin!• TnT:!binds!to!tropomyosin!and!helps!position!it!on!actin!• TnC:!binds!calcium!ions!• Sarcoplasmic!reticulum!and!T!tubules!o
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