Histology, Lecture 5, Muscular Tissue (slides)

8/8/2019 Histology, Lecture 5, Muscular Tissue (slides)

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Muscular TissueMuscular Tissue



Composed of diff erent cells containing the contractileComposed of diff erent cells containing the contractile

f ibersf ibers

Most of muscle cells are mesodermal in originMost of muscle cells are mesodermal in origin

Three ty pes of muscle f ibers can be distinguished Three ty pes of muscle f ibers can be distinguished

according to mor phological and f unctional diff erencesaccording to mor phological and f unctional diff erences



Sk eletal MuscleSk eletal Muscle

Long thin multinucleated f ibersLong thin multinucleated f ibers

1010--100100 µm in diameter and may reachµm in diameter and may reach 7070 cm in lengthcm in length

Peri pheral f lat nucleiPeri pheral f lat nuclei

Red in color due to m yoglobinRed in color due to m yoglobin

They are striated and attached to bone They are striated and attached to bone

Sarcoplasmic reticulum, Sarcoplasmic reticulum,

sarcolemma, sarcoplasmsarcolemma, sarcoplasm H y pertrophyH y pertrophy andand hy per plasiahy per plasia



Organization of Sk eletal MuscleOrganization of Sk eletal Muscle

E pim ysiumE pim ysium Perim ysiumPerim ysium

Endom ysiumEndom ysium

Connective tissue serves in:Connective tissue serves in: Transmits the force generated Transmits the force generated

by individual f ibersby individual f ibers

Blood and lymphatic vesselsBlood and lymphatic vessels

run in the connective tissuerun in the connective tissue



Organization of Sk eletal FiberOrganization of Sk eletal Fiber

In a sarcomere, identif y the follow ingIn a sarcomere, identif y the follow ing A A--band and m yosin f ilamintsband and m yosin f ilamints

II--band and actin f ilamentsband and actin f ilaments

Z line andZ line and actininactinin

M line and creatine k inaseM line and creatine k inase

H bandH band



Sarcoplasmic ReticulumSarcoplasmic Reticulum

De plarization at m yoneural junction leads to relaese of De plarization at m yoneural junction leads to relaese of CaCa+2+2

Transverse (T) tubules: invagination of sarcolemma at Transverse (T) tubules: invagination of sarcolemma at

the level of A the level of A--I bandsI bands

Triade: T Triade: T--tubule w ith dilatedcisternaetubule w ith dilatedcisternae

of sarcoplasmic reticulum at the sidesof sarcoplasmic reticulum at the sides

of Tof T--Tubule Tubule

Rigor MortisRigor Mortis



Contraction of Sk eletal MuscleContraction of Sk eletal Muscle

A A--bandband

II--bandband

Z linesZ lines

HH--bandband MM--lineline

ZZ--lineslines



InnervationInnervation

Myoneural JunctionMyoneural Junction

StructureStructure

Motor UnitMotor Unit

Myasthenia gravisMyasthenia gravis



Ty pes of Sk eletal Fibers Ty pes of Sk eletal Fibers

Ty pe I Ty pe I: Red Oxidative or Slow : Red Oxidative or Slow

Ty pe IIa Ty pe IIa: Red, Fast, Intermediate Oxidative: Red, Fast, Intermediate Oxidative

Ty pe IIb Ty pe IIb: White, Fast, Glycolytic: White, Fast, Glycolytic



Cardiac Muscle FiberCardiac Muscle Fiber

Striated w ith central round nucleus They areStriated w ith central round nucleus They are 1010xx100100µmµm

Short branching f ibersShort branching f ibers

Endom ysium surroundsEndom ysium surrounds

each muscle f ibereach muscle f iber Intercalated discsIntercalated discs

Fascia adherens (Actin)Fascia adherens (Actin)

Macula adheresMacula adheresGa p junctionGa p junction



Characteristics of Cardiac MuscleCharacteristics of Cardiac Muscle

More TMore T--Tubules and form diads at Z Tubules and form diads at Z--LineLine

Sarcoplasmic reticulum is lessSarcoplasmic reticulum is less

profound and irregularly dis persed profound and irregularly dis persed

Contain numerous mitochondriaContain numerous mitochondria((4040% vz% vz 22%)%)

Fatty acids are stored inFatty acids are stored in

li pid dropletsli pid droplets

Li pof uscin pigmentsLi pof uscin pigments Membrane bound granulesMembrane bound granules

containcontain Atrial Natriuretic Factor Atrial Natriuretic Factor

act on k idney leads to act on k idney leads to

Na and HNa and H O lossO loss



Smooth Muscle FiberSmooth Muscle Fiber

Consists of elongated, nonConsists of elongated, non--striated muscle f ibersstriated muscle f ibers It is surrounded by a basal lamina and reticular f ibersIt is surrounded by a basal lamina and reticular f ibers

It has a central o v oid nucleus andIt has a central o v oid nucleus and

other cytoplasmic organellesother cytoplasmic organelles

Ill developed sarcoplasmicIll developed sarcoplasmicreticulum is not organized to reticulum is not organized to

tubulestubules

Contains thin f ilaments madeContains thin f ilaments made

of actin and tropom yosin andof actin and tropom yosin and

thick f ilaments made of m yosinthick f ilaments made of m yosin

Intermediate f ilaments (Intermediate f ilaments (Desmin and VimentinDesmin and Vimentin))

Dens bodiesDens bodies (Membranous and cytoplasmic)(Membranous and cytoplasmic)



Ty pes of Smooth Fibers Ty pes of Smooth Fibers

Visceral: in the w all of viscera .They have ga p Visceral: in the w all of viscera .They have ga p

junctions and poor nerve su pply and contract injunctions and poor nerve su pply and contract in

syncytial f ashion (Bulk contraction)syncytial f ashion (Bulk contraction)

Multiunit: In the iris of the eye. They have richMultiunit: In the iris of the eye. They have rich

innervation (Graded and precise action)innervation (Graded and precise action)



Mechanism of contractionMechanism of contraction

In sk eletal and cardiac muscle f ibers, calcium binds to In sk eletal and cardiac muscle f ibers, calcium binds to troponin leading to change in the geometry of thin andtroponin leading to change in the geometry of thin and

thick f ilaments leading to contraction (sliding theory).thick f ilaments leading to contraction (sliding theory).

In smooth muscle f iber, calcium binds to calmodulinIn smooth muscle f iber, calcium binds to calmodulin

w hich activate m yosin light chian k inase leading to w hich activate m yosin light chian k inase leading to

m yosin phos pholyrationm yosin phos pholyration

Factors leading to increase or decrease cAMP levelsFactors leading to increase or decrease cAMP levels

leads to contraction and relax

ation, res pectivelyleads to contraction and relax

ation, res pectively



Regeneration of Muscle TissueRegeneration of Muscle Tissue

Injured cardiac f ibers af ter childhood are re placedInjured cardiac f ibers af ter childhood are re placedby f ibrous tissueby f ibrous tissue

Injured sk eletal f ibers have limited potential forInjured sk eletal f ibers have limited potential for

regeneration. Satellite cells (Undiff erentiatedregeneration. Satellite cells (Undiff erentiatedm yoblasts) w ithin the basal lamina of sk eletalm yoblasts) w ithin the basal lamina of sk eletalf ibers become activated and prolif erate and f usef ibers become activated and prolif erate and f usetogether to give ne w muscle f iberstogether to give ne w muscle f ibers

Injured smooth f ibers have active regenerativeInjured smooth f ibers have active regenerativeactivityactivity



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Histology, Lecture 5, Muscular Tissue (slides)

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