His to Muscle

8/14/2019 His to Muscle

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Muscular tissue:Muscular tissue:

General considerationsGeneral considerations

germ layer origin:germ layer origin: MesodermMesoderm parenchymal cell:parenchymal cell: muscle fibermuscle fiber//

myocyte/ muscle cellmyocyte/ muscle cell major function: movementmajor function: movement main component: contractilemain component: contractile

proteinsproteins ActinActin && MyosinMyosin in the formin the formof myofibrils / microfilamentsof myofibrils / microfilaments


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Muscle tissue terminologyMuscle tissue terminology

Sarcoplasm-Sarcoplasm- cytoplasm of muscle cells,cytoplasm of muscle cells,matrix in which myofibrils are suspended;matrix in which myofibrils are suspended;high in K, Mg, PO4; many mitochondriahigh in K, Mg, PO4; many mitochondria

Sarcoplasmic reticulum-Sarcoplasmic reticulum- endoplasmicendoplasmicreticulum of muscle cellsreticulum of muscle cells

Sarcolemma-Sarcolemma- cell membrane of musclecell membrane of muscle

cells, with a thin polysaccharide coat;cells, with a thin polysaccharide coat;fuses with tendon fibers at the ends offuses with tendon fibers at the ends ofmuscle fibersmuscle fibers


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Contractile Proteins : ActinContractile Proteins : Actin

Actin:Actin: 42kD42kD

G actin-G actin- globularglobularsubunits 5.5subunits 5.5 mmdiameterdiameter

F actin-F actin- two chains oftwo chains ofG actin wound togetherG actin wound togetherin a loose spiral within a loose spiral with

3636m periodicitym periodicity


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ACTINACTINregulatory proteins:regulatory proteins:

TropomyosinTropomyosin- 2 intertwined- 2 intertwined helices, 40helices, 40m long,m long,covers 7 G-actin units, bound to troponin at onecovers 7 G-actin units, bound to troponin at oneend, lies in the groove of the F-actin helix,end, lies in the groove of the F-actin helix,covering the Myosin-binding site when intracellularcovering the Myosin-binding site when intracellularCa is lowCa is low

TroponinTroponin- complex of 3 globular subunits:- complex of 3 globular subunits:TnTTnT(tropomyosin-binding site),(tropomyosin-binding site), TnCTnC(calcium binding(calcium binding

site ), &site ), & TnITnI(inhibits Actin-Myosin interaction)(inhibits Actin-Myosin interaction) -Actinin--Actinin- binds to ends of thin filaments (inbinds to ends of thin filaments (in

striated muscles, at the Z lines of the sarcomere)striated muscles, at the Z lines of the sarcomere)


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Actin & Myosin interactionActin & Myosin interaction


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Types of Muscle TissueTypes of Muscle Tissue

Smooth muscle-Smooth muscle- nonstriated fusiform cellsnonstriated fusiform cellsunder autonomic/involuntary control;under autonomic/involuntary control;contraction is slowcontraction is slow

Cardiac muscle-Cardiac muscle- striated elongated branchedstriated elongated branchedtubular cells under autonomic/ involuntarytubular cells under autonomic/ involuntarycontrol; contraction is vigorous & rhythmiccontrol; contraction is vigorous & rhythmic

Skeletal muscle-Skeletal muscle- very long cylindricalvery long cylindricalmultinucleated striated cells in bundles undermultinucleated striated cells in bundles undervoluntary control; quick, forceful contractionsvoluntary control; quick, forceful contractions


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Types of MuscleTypes of Muscle


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Smooth MuscleSmooth Muscle

CellsCells- elongated, fusiform, nonstriated,- elongated, fusiform, nonstriated,each enclosed by a basal lamina & aeach enclosed by a basal lamina & anetwork of reticular fibers (collagen typenetwork of reticular fibers (collagen type

III); 20-500III); 20-500m ; central nucleus; inter-m ; central nucleus; inter-digitate to form closely-packed sheetsdigitate to form closely-packed sheets

OrganellesOrganelles- rudimentary sarcoplasmic- rudimentary sarcoplasmicreticulum; abundant perinuclearreticulum; abundant perinuclear

mitochondria, free ribosomes in clusters,mitochondria, free ribosomes in clusters,modest Golgi apparatusmodest Golgi apparatus


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Smooth muscleSmooth muscle


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Contractile proteins-Contractile proteins- bundles of myofilamentsbundles of myofilamentscriss-cross obliquely, forming a lattice-likecriss-cross obliquely, forming a lattice-likenetwork with much actin overlap;network with much actin overlap;

thin filaments: 5-7nm,thin filaments: 5-7nm, actinactin && tropomyosintropomyosin;;

thick filaments: 12-16nm,thick filaments: 12-16nm, myosinmyosin;;intermediate filaments: 10nm,intermediate filaments: 10nm, vimentinvimentin &&desmindesmin (skeletin)(skeletin)

Dense bodies-Dense bodies- membrane-associated &membrane-associated &cytoplasmic- containcytoplasmic- contain -actinin-actinin; where thin &; where thin &intermediate filaments insertintermediate filaments insert


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Smooth MuscleSmooth Musclevisceralvisceral muscle- a muscle- a functional syncytiumfunctional syncytium onon

account of numerous gap junctions betweenaccount of numerous gap junctions betweencellscells

Nervous control-Nervous control- involuntaryinvoluntary (ANS)-(ANS)-modifying action rather than initiatingmodifying action rather than initiating

Contraction- slow, concerted- borders of theContraction- slow, concerted- borders of thecell become scalloped, nucleus becomes foldedcell become scalloped, nucleus becomes folded

(like a corkscrew); can also occur as in the(like a corkscrew); can also occur as in thesliding filamentsliding filament mechanism, where thin mechanism, where thin(Actin) filaments are stable & thick (Myosin)(Actin) filaments are stable & thick (Myosin)filaments are labilefilaments are labile


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Smooth muscle locationsSmooth muscle locations

walls of hollow viscerawalls of hollow viscera GITGIT

Respiratory tractRespiratory tract Genito-Urinary tractGenito-Urinary tract Blood vessel wallsBlood vessel walls

Arrectores pilorumArrectores pilorum IrisIris Ciliary bodyCiliary body


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Smooth Muscle contractionSmooth Muscle contraction

Influx ofInflux of CalciumCalcium Calcium complexes withCalcium complexes with CalmodulinCalmodulin

Ca-Calmodulin complex activatesCa-Calmodulin complex activatesenzymeenzyme myosin light-chain kinasemyosin light-chain kinase Myosin light-chain kinaseMyosin light-chain kinase

phosphorylates myosin light chainphosphorylates myosin light chain MyosinMyosin interacts withinteracts with ActinActin ContractionContraction

Striated M scles Cardiac &tr ate M sc es ar ac


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Striated Muscles: Cardiac &tr ate Musc es: ar acSkeletalSkeletal

Common features:Common features: cytoplasmic cross-striations (alternatingcytoplasmic cross-striations (alternating

dark A & light I bands) due to thedark A & light I bands) due to the

arrangement of myofilaments;arrangement of myofilaments;

SarcomereSarcomere- smallest repetitive subunit of- smallest repetitive subunit of

the contractile apparatus- consists ofthe contractile apparatus- consists ofan A band flanked by halves of an Ian A band flanked by halves of an Iband; extends from one Z line (midpointband; extends from one Z line (midpoint ofofI band) to anotherI band) to another


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SarcomereSarcomere


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Striated Muscle featuresStriated Muscle features

T tubulesT tubules - invaginations of the- invaginations of thesarcolemma penetrating the fiber,sarcolemma penetrating the fiber,interlacing with myofibrilsinterlacing with myofibrils

Sarcoplasmic reticulum forms aSarcoplasmic reticulum forms aLLongitudinalongitudinal tubulartubular system insystem inclose proximity to myofilamentsclose proximity to myofilaments

in the cytoplasm, with Calcium-in the cytoplasm, with Calcium-rich expanded ends-rich expanded ends- cisternaecisternae


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Diads & TriadsDiads & Triads

Close associations between T & L tubulesClose associations between T & L tubules Diads Diads in cardiac muscles 1 T tubulein cardiac muscles 1 T tubule

& 1 SR cistern& 1 SR cistern

Triads Triads in skeletal muscles 1 T tubulein skeletal muscles 1 T tubule& 2 SR cisternae& 2 SR cisternae


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Cardiac MuscleCardiac Muscle

Cells: in tightly knit bundles; 15Cells: in tightly knit bundles; 15m inm indiameter, 85-100diameter, 85-100m long; striated,m long; striated,elongated, branching, each with aelongated, branching, each with acentral pale nucleus & surrroundedcentral pale nucleus & surrrounded

by a delicate endomysium rich inby a delicate endomysium rich incapillaries;capillaries;

Intercalated disks-Intercalated disks- gap junctions atgap junctions atthe intersections between cells,the intersections between cells,

areas of low resistance to ionic flowareas of low resistance to ionic flow


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Organelles: numerous mitochondria,Organelles: numerous mitochondria,parallel arrangement;parallel arrangement; irregularirregularsarcoplasmic reticulumsarcoplasmic reticulum (longitudinal(longitudinal

tubular system) among the myo-tubular system) among the myo-filaments, ending in expandedfilaments, ending in expanded cisternaecisternae

Sarcolemma invaginates periodically atSarcolemma invaginates periodically at

the level of the Z bands, producingthe level of the Z bands, producingnumerous,numerous, large T tubuleslarge T tubules DiadDiad- one T tubule & one sarcoplasmic- one T tubule & one sarcoplasmic

reticulum cisternareticulum cisterna


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innervation- autonomic nerves- involuntaryinnervation- autonomic nerves- involuntary locations:locations: myocardiummyocardium

origins of great vesselsorigins of great vessels (Aorta,(Aorta,Venae Cava, Pulmonary Artery)Venae Cava, Pulmonary Artery)from the heartfrom the heart

modified cardiac myocytes:modified cardiac myocytes:

Purkinje cellsPurkinje cells nodal cellsnodal cells


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Skeletal MuscleSkeletal Muscle

Cells- long cylindrical multinucleatedCells- long cylindrical multinucleatedfibers with cytoplasmic cross-striations &fibers with cytoplasmic cross-striations &

peripherally oriented nuclei oriented inperipherally oriented nuclei oriented in

bundles (bundles (fasciclesfascicles)) Connective tissue coverings:Connective tissue coverings:

endomysiumendomysium-covers individual fibers;-covers individual fibers;

perimysiumperimysium- covers each fascicle;- covers each fascicle;epimysiumepimysium- covers the entire muscle- covers the entire muscle Satellite cells-Satellite cells- small cells that may play asmall cells that may play a

role in regeneration of injured musclerole in regeneration of injured muscle


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Skeletal muscleSkeletal muscle


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Skeletal muscle fibersSkeletal muscle fibersRedRed (slow twitch) fibers- contain(slow twitch) fibers- contain myoglobinmyoglobin--

in sustained/ postural movementsin sustained/ postural movements

WhiteWhite (fast twitch) fibers- in(fast twitch) fibers- in

muscles for rapid, precise, finemuscles for rapid, precise, finemovementsmovementsIntermediateIntermediate fibers- intermediatefibers- intermediate

features red, but fast twitchfeatures red, but fast twitch


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Sarcoplasmic reticulumSarcoplasmic reticulum is well-developed,is well-developed,longitudinally arranged tubules ending inlongitudinally arranged tubules ending inexpanded ends called cisterns/ terminalexpanded ends called cisterns/ terminalcisterns, which containcisterns, which contain CalsequestrinCalsequestrin &&

high Calcium levelshigh Calcium levels T tubules-T tubules- invaginations of the sarcolemmainvaginations of the sarcolemma

penetrating deep into the interior of thepenetrating deep into the interior of themuscle fiber at the junction of the A & Imuscle fiber at the junction of the A & I

bands, forming a grid perforated bybands, forming a grid perforated bymyofibrilsmyofibrils

TriadTriad- association of one T tubule with two- association of one T tubule with two

terminal cisterns of the SR (2/sarcomere)terminal cisterns of the SR (2/sarcomere)


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Skeletal muscleSkeletal muscle

Innervation: voluntary Innervation: voluntary motor nervesmotor nerves

exceptionsexceptions :: reflex arcsreflex arcs Motor end-plate/myoneural junction/Motor end-plate/myoneural junction/

neuromuscular junctionneuromuscular junction Location- attached to bones-Location- attached to bones-

exceptionsexceptions:: upper1/3, esophagusupper1/3, esophagus;;

tonguetongueExamples : gastrocnemius, gluteus,Examples : gastrocnemius, gluteus,

trapezius, deltoid, soleus, frontalistrapezius, deltoid, soleus, frontalissternocleidomastoid, massetersternocleidomastoid, masseter,,


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Striated muscle contractionStriated muscle contraction

nerve impulse is propagated along thenerve impulse is propagated along thesarcolemma, along the invaginated Tsarcolemma, along the invaginated Ttubules to the diads / triadstubules to the diads / triads

Ca is released from the SR cisternae toCa is released from the SR cisternae tothe sarcoplasmthe sarcoplasm

Ca binds to TnC, configurational changeCa binds to TnC, configurational changeexposes myosin-binding sites on G actinexposes myosin-binding sites on G actin

ATPase cleaves ATPATPase cleaves ATPMyosin binds to ActinMyosin binds to Actin muscle contraction occursmuscle contraction occurs


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Actin & Myosin interactionActin & Myosin interaction


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