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MUSCLE IS A BASIC TISSUEMUSCLE IS A BASIC TISSUE DEFINITION: Muscle isDEFINITION: Muscle is a tissuea tissue

specialized for contraction andspecialized for contraction andtransmission of im ulsestransmission of im ulses

Extreme example of specializationExtreme example of specialization

functionsfunctions

Almost always associated withAlmost always associated with

nervous ssuenervous ssue

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THINGS COMMON TOTHINGS COMMON TOALLALL

Contraction is due to ACTIN andContraction is due to ACTIN and

MYOSIN microfilamentsMYOSIN microfilaments Contraction is an all or none responseContraction is an all or none response

Force of contraction is transmittedForce of contraction is transmitted

through a network of collagenous fibersthrough a network of collagenous fibers

Origin is from embryonic mesodermOrigin is from embryonic mesoderm

capabilitiescapabilities

Loss of ability to divideLoss of ability to divide

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SMOOTH MUSCLESMOOTH MUSCLE Hormonal, nervous,Hormonal, nervous,

and physical stimuliand physical stimuli

Involuntary orInvoluntary or

visceralvisceral

smooth musclesmooth muscle ResponsiveResponsive

designation notdesignation notalways accuratealways accurate

contract oncontract on nnintestineintestine

Nervous stimulationNervous stimulation

Occurs widely in mostOccurs widely in most

organs and in fibrousorgans and in fibrousvia sympathetic andvia sympathetic andparasympatheticparasympatheticroutesroutes

Can be single cells,Can be single cells,

ContractionsContractionsusually strong,usually strong,

large sheetslarge sheets

Also in skin & e eAlso in skin & e esus a ne , an s owsus a ne , an s ow

among other placesamong other places

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SMOOTH MUSCLE CELLSSMOOTH MUSCLE CELLS Spindle shapedSpindle shaped

Lie adjacent to each other in sheetsLie adjacent to each other in sheets

Single central nucleusSingle central nucleus

Nuclei are bluntNuclei are blunt--ended or cigar shapedended or cigar shaped

s ows m cro amen s p nocy o c vacuo ess ows m cro amen s p nocy o c vacuo es

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ASSOCIATION OFASSOCIATION OF

SMOOTH MUSCLESMOOTH MUSCLECELLSCELLS

Adjacent cellsAdjacent cellshavehavegapgap

communicatecommunicate

vesiclesvesicles

resentresent

Ingestion ofIngestion of

hormones,hormones,

neuro ransmneuro ransm

tters, etc.tters, etc.

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HISTOLOGYHISTOLOGY

MUSCLEMUSCLE

Cross sectionsCross sectionshavehavecharacteristiccharacteristicappearanceappearance

sections easilysections easilymistaken for CTmistaken for CT

onus causesonus causesnuclei tonuclei towrinkle orwrinkle orcorkscrew incorkscrew in

LSLS

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STRIATED MUSCLESTRIATED MUSCLE Two types: SKELETAL and CARDIACTwo types: SKELETAL and CARDIAC

More similar than they are differentMore similar than they are different Skeletal muscle the archetype for bothSkeletal muscle the archetype for both

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Muscle vsMuscle vs

Anatomic muscles canAnatomic muscles can

be consideredbe considered or ansor ans

All have namesAll have names PrincipalPrincipal tissuetissue inin

them is musclethem is muscle

CT is also presentCT is also present , .,, .,also presentalso present

Terminolo of levelsTerminolo of levelsof organization isof organization ishierarchicalhierarchical

reflects differentreflects differentlevels of activitylevels of activity

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ORGANIZATION INORGANIZATION IN

SKELETALSKELETAL

MUSCLESMUSCLES

un es emarca eun es emarca e

FASCICLESFASCICLES

Fascicles com osed ofFascicles com osed of

MYOFIBERSMYOFIBERS

Myofibers are cellsMyofibers are cells Myofibers containMyofibers contain

MYOFIBRILSMYOFIBRILS

filamentous subunitsfilamentous subunits

Myofibrils are made ofMyofibrils are made of

Actin and MyosinActin and Myosin

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SKELETAL MUSCLESKELETAL MUSCLE

Voluntary i.e.,Voluntary i.e., usuallyusuallyunder conscious controlunder conscious control

,,

necessarynecessary interactioninteractionwith nervous tissuewith nervous tissue

stimulistimuli

Most abundant formMost abundant form unct onunct on toto prov e orprov e or

movementmovement

Affected by hormones,Affected by hormones,

nutrition, disease, etc.nutrition, disease, etc. Cross striations areCross striations are

Very large cellsVery large cells

Blood vessels betweenBlood vessels between

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MYOFIBERMYOFIBER

EACH myofiber is aEACH myofiber is aSINGLE CELLSINGLE CELL

Ma have 1000s of nucleiMa have 1000s of nuclei

100100--150 microns diameter150 microns diameter

A single Myofibers may beA single Myofibers may beseveral FEET longseveral FEET long

g y spec a zeg y spec a ze

Cannot divideCannot divide

Packed with contractilePacked with contractile

and in REGISTER with eachand in REGISTER with eachotherother

Cytoplasm almostCytoplasm almost

materialmaterial Sarcomeres laid end toSarcomeres laid end to

end like railroad carsend like railroad cars

Each myofibril isEach myofibril isanchored at the ends ofanchored at the ends ofthe myofiberthe myofiber

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SARCOMERE TOSARCOMERE TO

MYOFILAMENTSMYOFILAMENTS

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FROM Z TO SHINING Z: THE SARCOMEREFROM Z TO SHINING Z: THE SARCOMERE

Each myofiber has millions of them in seriesEach myofiber has millions of them in series

Sarcomeres contract about 0.4 microns eachSarcomeres contract about 0.4 microns each

Sarcomeres made of actin & myosin microfilamentsSarcomeres made of actin & myosin microfilaments

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ORIGIN OF THEORIGIN OF THE

BANDINGBANDING

PATTERNPATTERN

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T-tubules carry the

outside inside

Close to SER but

physically separated

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CARDIAC MUSCLECARDIAC MUSCLE A form of striated muscle

Found only in the heart Structurally similar to skeletal

e s are sma er

Specialized communication structures

Histolo somewhat different Responsive to different stimuli

Contraction is an inherent property

o rect neura st mu at on nee e No NMJ!

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HISTOLOGY OF CARDIACHISTOLOGY OF CARDIAC

Anastomosing fibersAnastomosing fibers

Cells are much smaller than skeletalCells are much smaller than skeletal MonoMono--nucleatednucleated

Many capillaries visibleMany capillaries visible

CM cannot incur an oxygen debt!CM cannot incur an oxygen debt!

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CARDIACCARDIAC

IndividualIndividual

Nucleus inNucleus incentercenter

faintfaint

UniqueUnique

--CALATEDCALATEDDISKDISK

DiagnosticDiagnosticfeature offeature ofCM!CM!

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In CrossIn CrossSection:Section:

CENTER ofCENTER of

Cells all aboutCells all aboute same s zee same s ze

ProportionallyProportionally

more nucleimore nucleiper unit areaper unit area

than Smooththan Smooth

musclemuscle

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THREE CROSS SECTIONSTHREE CROSS SECTIONS

LEFT TO RIGHT: Cardiac, Skeletal, SmoothLEFT TO RIGHT: Cardiac, Skeletal, Smooth

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CARDIACCARDIAC

MYOCYTESMYOCYTES

same origin assame origin asSkeletal cellsSkeletal cells

Length 70Length 70--100100

micronsmicrons --micronsmicrons

CM FibersCM Fibers

composed ofcomposed ofcells attachedcells attached

-- --

TOP: SEM of myocyte; BOTTOM: Isolated cells

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INTERCALATED DISKSINTERCALATED DISKS SpecialSpecial

structure forstructure for

--

CATION &CATION &ADHESIONADHESION

33--D interlockingD interlocking

of adjacent cellsof adjacent cells

atat endsends

ID includesID includes

adheringadhering

unc ons gapunc ons gapjunctionsjunctions

CommunicationCommunication

& adhesion site& adhesion site

for CMfor CM

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NEURAL RELATIONSHIPS INNEURAL RELATIONSHIPS IN

Vary with type

SKELETAL muscle most elaborate

SMOOTH muscle simple but direct

CARDIAC muscle controlled b non-

neural network & internally

Control is monitored closely by CNS

Structures exist for this purpose

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M T R END PLATEM T R END PLATE

Skeletal muscleSkeletal muscle

Lacking inLacking in

smooth andsmooth and

cardiac musclecardiac muscle

Transmission ofTransmission of

si nal fromsi nal from

nervous system tonervous system to

muscle is chemicalmuscle is chemical

SpecializedSpecialized

structure in PM ofstructure in PM of

myofibermyofiberONE ANDONE AND ONLYONLY

ONEONE NM ONNM ON

ANY GIVENANY GIVEN

MYOFIBERMYOFIBER

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Muscle Fiber

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MOTORMOTOR

UNITUNIT

ONE axon controlsONE axon controls

several myofibersseveral myofibers

The axon and itsThe axon and its

single MOTOR UNITsingle MOTOR UNIT

Switching motor unitsSwitching motor units

on and off regulates &on and off regulates &sustains forcesustains force

control mechanismcontrol mechanism

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NEURALNEURAL

IN SMOOTHIN SMOOTH

NO elaborateNO elaborate

NMJNMJ

Nerve fibersNerve fibersend on cellsend on cells

NeurotransNeurotrans--

mitter uptakemitter uptakeby pinocytosisby pinocytosis

an or an or

diffusiondiffusion

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MUSCLEMUSCLE

SPINDLESPINDLE

A control device forA control device for

skeletal muscleskeletal muscle Works like aWorks like a

thermostatthermostat

Sensory & neuralSensory & neuralfibersfibers

muscle fibersmuscle fibers

Set point can beSet point can bemodified asmodified asnee enee e

More numerousMore numerouswhere fine control iswhere fine control is

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SPINDLE LIES AMONG FIBERSSPINDLE LIES AMONG FIBERS

Detects tension changes & reportsDetects tension changes & reports

Brain reBrain re--sets as neededsets as needed

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COLLAGEN NETWORKCOLLAGEN NETWORK

All muscle cells are invested by CTAll muscle cells are invested by CT

CT forms a basketwork around cells and connectsCT forms a basketwork around cells and connects

to higher levelsto higher levels

Force is transmitted through CTForce is transmitted through CT

No CT, no work!No CT, no work!

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REGENERATION ANDREGENERATION AND

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REGENERATION ANDREGENERATION AND

Muscle cells cant divideMuscle cells cant divide

Injury usually causes some loss of material, partInjury usually causes some loss of material, part

Scarring fills in the space with collagenScarring fills in the space with collagen

Colla en is nonColla en is non--contractilecontractile A scanty reserve of myoblasts exists inA scanty reserve of myoblasts exists in

skeletal muscleskeletal muscle

Not in smooth or cardiacNot in smooth or cardiac MAY be some LIMITED regeneration fromMAY be some LIMITED regeneration from

these but not much!these but not much!

Never in cardiac muscleNever in cardiac muscle

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ATROPHYATROPHY

Loss of muscleLoss of musclemassmass

NUMBER ofNUMBER ofchangechange

Decrease inDecrease invo ume, oss ovo ume, oss ocontractilecontractileelementselements

Often reversibleOften reversible

CAUSES OFCAUSES OF

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CAUSES OFCAUSES OF

ATROPHYATROPHY

DisuseDisuseMalnutritionMalnutrition

Nerve dama eNerve dama e

DiseaseDisease

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HYPERTROPHYHYPERTROPHY

With constant useWith constant use

undergoesundergoesHYPERTOPHYHYPERTOPHYOF USEOF USE

Number of cellsNumber of cellsoes not c angeoes not c ange

Amount ofAmount of

in EACH myofiberin EACH myofiberincreasesincreases

AN EXAMPLE OFHYPERTROPHY OF USE

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