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Departmentofe u aran ys o og ca c ences

MuscleTissue

Presentedby:Dr.M.Alimohammadima :ma a n erc ange.u c.ca

Phone:(604)822 7545

LectureOutline1. Terminologyofmusculartissue.

2. Classificationofmusculartissue.

3. Majorhistologicalfeaturesofskeletalandsmoothmuscletissues.

4. Contractionmechanism(slidingfilamenttheory)

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MuscularTissue

OriginatesfromMesodermandis

v e ntotwo

majorgroups: Striated foundas:

1. Skeletalmuscle(voluntarily)

2. Cardiacmuscle

Smooth;

oun n ewa o hollowviscera,blood

vessels,anddermisoftheskin. F.4.1

Muscle Cell Fiber

Sarcolema Cellmembrane

Sarcoplasm Cytoplasm

SarcoplasmicReticulum E.R

Sarcosome Mitochondria

yo amen cro amen

Myoglobin Pigment

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SkeletalMuscle&Myofibrils

Iscomposedoflongcylindrical,multinucleatedcells.

Musclefibersareindividually surroundedbyalayerofCT

anotherlayerofCT(perimysium).FinallythewholemuscleiswrappedbyathirdlayerofCT(epimysium).

Withineachmusclefibertherearebundles(myofibril)ofmyofilaments

Each m ofibril is surrounded b an interconnected networkofER(sarcoplasmic reticulum).

Alsoamongthesemyofibrils,numerousmitochondia .

Themyofibrilsshowlight(I)anddark(A)bands(striations).

F.4.3

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F.4.4

Myofilaments Therearetwotypesof

myofilaments:1. Thick(myosin);1.6 m

ongan nm ndiameter,madeupofmyosinmoleculeswith

(meromyosins).2. Thin(actin);1 mlong

,madeupofactin (f),troponin,andtro om osin.

Bothfilamentsareattached(actin,directlyandmyosin,indirectly)toZdisks.

F.4.8

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Thatpartofthemyofibril

w c soccup e y o

typesofmyofilaments

re resenttheAband,

whilethosepartswhich

containjustthethinor

filamentsareknownasI

andHbandsres ectivel .

Duringmusclecontraction,thewidthofI,andHbands

shorteningofsarcomeres.

F.4.8

SarcotubularSystem Thetwoendsof

reticularnetwork

myofibrils,enlargetoformterminalc s ernae.

Thetwoadjacent

cisternaeareseparatedbyatransversetubule

F.4.7

thesarcolemma),andalltogetherreferredtoasTriad.

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SlidingFilamentTheory

Isexplainedasthefollowingsequences:1. Animpulseistransmittedintotheinteriorofthefibervia

transversetu u e.

2. Calciumionsleavetheterminalcisternaandenterthecytosole.3. Conformationalchangesintroponininthepresenceof

calciumions,causesthetropomyosintosinkdown,exposingtheactivesiteofactin.

. y ro ysiso to an ap osp ategroupatt epresenceofMgions.

5. Formationofastrongbondbetweenactinandmyosinw e emyos nmo ecu e en s.

6. AnotherATPmoleculebindstothemyosin,leadingtoits

detachmentfromactin.

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SkeletalMuscleFiberTypes

1. Red(typeI),aerobic,slowtwitchwithhighendurance.Containnumerousmitochondria,andmyoglobin (postural

.

2. White(typeIIB),anaerobic fast

twitch,andcapableof

producinghigh

force.Contain

fewmitochondria

3. Intermediate

(typeIIA).

F.4.12

SmoothMuscle Fusiform(spindleshaped)mononucleatedcellswithno

striation.

.acidophilicandthenucleusiscentrallylocated.

EachcellisindividuallysurroundedbyathinlayerofCT.

Themostimportant

functionofsmoothmuscletissueis

peristaltic

movementso

tractandalso

constriction of

bloodvessels.F.4.25

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SmoothMuscleContraction

scon rac on ss ower,moreenergyefficient,moresustainable,andshowslessfatiguecomparedtos e eta musc et ssue.

Therearethreedifferenttypesofmyofilaments:

Thick(myosin),Thin(actin),and

Intermediate(desmin/vimentin). F.4.26 ese amen sare

attachedtoeachother

insidethec to lasmand

alsotothecellmembrane

bymeansofDenseBodies(Zbandequivalent).