Macroscopic & Microscopic Structure of Muscular System

Macroscopic &Macroscopic &
Microscopic ofMicroscopic of
Muscular SystemMuscular System
HERMIZAN HALIHANAFIAH

Lesson ObjectiveLesson Objective
By the end of this 2 hours lecture, student will beBy the end of this 2 hours lecture, student will be
able to:able to:
1.1. State the types of muscle tissuesState the types of muscle tissues
2.2. Explain the microscopic structure of skeletal musclesExplain the microscopic structure of skeletal muscles
3.3. Explain the structure and function of the tendonExplain the structure and function of the tendon
4.4. Explain microscopic structure of cardiac musclesExplain microscopic structure of cardiac muscles
5.5. Explain microscopic structure of smooth musclesExplain microscopic structure of smooth muscles
6.6. State the properties of musclesState the properties of muscles
7.7. State the functions of the muscular systemState the functions of the muscular system

IntroductionIntroduction
 Movement of theMovement of the
limbs, the heart andlimbs, the heart and
other parts of theother parts of the
body are made bybody are made by
muscular system.muscular system.

Types of Muscle TissuesTypes of Muscle Tissues
3 types of muscular tissues:3 types of muscular tissues:
1.1. Skeletal muscle tissueSkeletal muscle tissue
2.2. Cardiac muscle tissueCardiac muscle tissue
3.3. Smooth muscle tissueSmooth muscle tissue

Microscopic Structure of SkeletalMicroscopic Structure of Skeletal
Muscles TissueMuscles Tissue
 Multinucleated cellsMultinucleated cells
 Derived from myoblast precursor cells.Derived from myoblast precursor cells.
 Three layers of connective tissue extend formThree layers of connective tissue extend form
fascia to protect and strengthen skeletal muscles.fascia to protect and strengthen skeletal muscles.
 Epimysium, perimysium and endomysium.Epimysium, perimysium and endomysium.

 Epimysium – outermost layer, encircle the entireEpimysium – outermost layer, encircle the entire
muscles.muscles.
 Perimysium – surround 10 – 100 or more fiber,Perimysium – surround 10 – 100 or more fiber,
separate muscle fiber into bundles calledseparate muscle fiber into bundles called
fascicles.fascicles.
 Endomysium – inside the fascicle, separatingEndomysium – inside the fascicle, separating
individual muscle fiber from one another.individual muscle fiber from one another.
Microscopic StructureMicroscopic Structure

 Important component – skeletal muscle fiberImportant component – skeletal muscle fiber
(muscle cells)(muscle cells)
 Diameter – 10 – 100Diameter – 10 – 100 μμm , length about 10 cm –m , length about 10 cm –
30 cm30 cm
 Develop from immature cells,Develop from immature cells, myoblastmyoblast
 Each matured skeletal muscle fiber consist aEach matured skeletal muscle fiber consist a
hundred or more nucleushundred or more nucleus (multinucleated).(multinucleated).

 The multiple nuclei are located just beneath the plasmaThe multiple nuclei are located just beneath the plasma
membrane of muscle cells calledmembrane of muscle cells called sarcolemmasarcolemma..
 Thousand of tiny invagination of sarcolemma calledThousand of tiny invagination of sarcolemma called
transverse (T) tubulestransverse (T) tubules, penetrate in from the surface, penetrate in from the surface
towards the centre of each muscle fiber.towards the centre of each muscle fiber.
 Within the sarcolemma is a cytoplasm of muscle fiberWithin the sarcolemma is a cytoplasm of muscle fiber
calledcalled sarcoplasmsarcoplasm..

 Within the sarcoplasm consist substantial substance ;Within the sarcoplasm consist substantial substance ;
glycogen and red colored protein calledglycogen and red colored protein called myoglobinmyoglobin..
 ConsistConsist many mitochondriamany mitochondria – highly active muscles– highly active muscles
 At high magnification, within the sarcoplasm containAt high magnification, within the sarcoplasm contain
myofibrilsmyofibrils, the, the contractile organellecontractile organelle of skeletalof skeletal
muscles.muscles.
 Myofibrils is about 2Myofibrils is about 2 μμm in diameter and extend them in diameter and extend the
entire length of a muscle fiber.entire length of a muscle fiber.
 Make the entire skeletal muscle fiber appearMake the entire skeletal muscle fiber appear striated.striated.

 A fluid filled system of membranous sacs called theA fluid filled system of membranous sacs called the
sarcoplamic reticulum (SR)sarcoplamic reticulum (SR) encircle each myofibril.encircle each myofibril.
 Dilated end sacs of the SR calledDilated end sacs of the SR called terminal cisternsterminal cisterns..
 AA tranverse tubultranverse tubul andand two terminal cisternstwo terminal cisterns form aform a
triadtriad..
 In theIn the relaxedrelaxed muscle fiber, themuscle fiber, the SR stores Ca2+.SR stores Ca2+.
 MusclesMuscles contractioncontraction occurred due tooccurred due to releasing Ca2+releasing Ca2+
from terminal cisterns of SRfrom terminal cisterns of SR..

 Within myofibrils are smaller structures calledWithin myofibrils are smaller structures called
filaments (myofilaments).filaments (myofilaments).
 2 types of filaments;2 types of filaments; thickthick andand thin filamentsthin filaments
 Thick filamentsThick filaments – 16nm diameter, 1-2– 16nm diameter, 1-2 μμm longm long
 Thin filamentsThin filaments –– 8 nm diameter, 1-28 nm diameter, 1-2 μμm longm long

Myofibril StructureMyofibril Structure
Thick FilamentThin Filament

 Both thick and thin filaments involved in theBoth thick and thin filaments involved in the
contractile process.contractile process.
 Overall there are two thin filaments for every thickOverall there are two thin filaments for every thick
filament in the regions of filament overlap.filament in the regions of filament overlap.
 Filaments in myofibrils arranged in compartment calledFilaments in myofibrils arranged in compartment called
sarcomeres.sarcomeres.
 Sarcomere is the basic functional units ofSarcomere is the basic functional units of
myofibrilsmyofibrils..

 Components of the sarcomereComponents of the sarcomere
1.1. Z discsZ discs
2.2. A bandA band
3.3. I bandI band
4.4. H zoneH zone
5.5. M lineM line

1.1. Z discsZ discs
 narrow, plated shaped regions of dense proteinnarrow, plated shaped regions of dense protein
meterial that separate one sarcomere from themeterial that separate one sarcomere from the
next.next.
2.2. A bandA band
 The dark, middle part of sarcomere, extendThe dark, middle part of sarcomere, extend
the entire length of thick filaments plusthe entire length of thick filaments plus
overlap area between thick and thin filament.overlap area between thick and thin filament.

3.3. I bandI band
 Lighter zone, contain the rest of thin filament but no thickLighter zone, contain the rest of thin filament but no thick
filamentsfilaments
4.4. H zoneH zone
 A narrow region in the center of each A band that containA narrow region in the center of each A band that contain
only thick filament and no thin filament.only thick filament and no thin filament.
5.5. M lineM line
 Region center of the H zone and contain protein that hold theRegion center of the H zone and contain protein that hold the
thick filament together at the center of sarcomerethick filament together at the center of sarcomere

Structure of the MyofibrilsStructure of the Myofibrils
 Muscle proteinMuscle protein
 Build up from three types of protein:Build up from three types of protein:
 Contractile proteinContractile protein – generate– generate forceforce duringduring
contractioncontraction
 Regulatory proteinRegulatory protein – help switch the contraction– help switch the contraction
process on and offprocess on and off
 Structural proteinStructural protein – keep the thick and thin filament– keep the thick and thin filament
in thein the proper alignmentproper alignment,, give elasticitygive elasticity andand
extensibility characteristics to myofibril.extensibility characteristics to myofibril.

Structure of the Myofibrils (continue)Structure of the Myofibrils (continue)
 Contractile protein –Contractile protein – myosin and actinmyosin and actin
 Regulatory protein –Regulatory protein – tropomyosin, troponintropomyosin, troponin
 Structural protein – titin,Structural protein – titin, αα – actinin, myomesin,– actinin, myomesin,
nebulin, and dystrophinnebulin, and dystrophin

 The role of actin proteinThe role of actin protein
Discovered byDiscovered by StraubStraub in 1942in 1942
 Hugh Huxley and Allan HuxleyHugh Huxley and Allan Huxley
1954 has found that the1954 has found that the
protein, myosin, contracting inprotein, myosin, contracting in
the presence of calcium ionsthe presence of calcium ions
 Found that skeletal musclesFound that skeletal muscles
shortens during contraction andshortens during contraction and
because the thick and thinbecause the thick and thin
filaments slide past one another.filaments slide past one another.
 So the model describing thisSo the model describing this
process is known as theprocess is known as the slidingsliding
filament mechanism.filament mechanism.
Contraction & Relaxation of SkeletalContraction & Relaxation of Skeletal
Muscles FiberMuscles Fiber

The Sliding Filament MechanismThe Sliding Filament Mechanism
The structure of the Myosin proteinThe structure of the Myosin protein
 Myosin fx as a motor protein in all types of muscleMyosin fx as a motor protein in all types of muscle
tissuestissues
 Converting the chemical energy in ATP to theConverting the chemical energy in ATP to the
mechanical energy of motion or production of forcemechanical energy of motion or production of force
 In skeletal system, aboutIn skeletal system, about 300 myosin molecules300 myosin molecules formform
aa single thick filamentssingle thick filaments..
 Each myosin molecule is shaped likeEach myosin molecule is shaped like two golf clubstwo golf clubs
twisted together.twisted together.

 The myosin tail (twisted golf club handles)The myosin tail (twisted golf club handles) point towards M linepoint towards M line inin
the center of sarcomere.the center of sarcomere.
 Tails of neighboring myosin lie parallel to one another forming theTails of neighboring myosin lie parallel to one another forming the
shaft of the thick filament.shaft of the thick filament.
 The two projection of each myosin molecules (golf club heads) areThe two projection of each myosin molecules (golf club heads) are
calledcalled myosin heads.myosin heads.
 The heads project outward from the shaft in spiraling fashion andThe heads project outward from the shaft in spiraling fashion and
extendingextending towards thin filaments.towards thin filaments.

The Structure Of the Actin ProteinThe Structure Of the Actin Protein
 Thin filament is anchored byThin filament is anchored by Z discZ disc
 Their main component ofTheir main component of thin filamentsthin filaments is theis the actinactin
proteinprotein
 Individual actin molecules join to form actin filamentIndividual actin molecules join to form actin filament
that is twisted into helix.that is twisted into helix.
 On each actin molecule is aOn each actin molecule is a myosin – binding site,myosin – binding site,
where awhere a myosin head can attach.myosin head can attach.

The Structure of the Tropomyosin and TroponinThe Structure of the Tropomyosin and Troponin
 Part of the thin filamentPart of the thin filament
 Tropomyosin in form of strandsTropomyosin in form of strands covered the myosin-covered the myosin-
binding site on actinbinding site on actin duringduring muscles relaxationmuscles relaxation, prevent, prevent
attachment of myosin heads.attachment of myosin heads.
 Tropomyosin are held in place byTropomyosin are held in place by troponintroponin..
 Troponin also is aTroponin also is a binding site for Cabinding site for Ca2+,2+,
causing musclescausing muscles
contraction.contraction.

The Contraction CycleThe Contraction Cycle
 At the onset of contraction,At the onset of contraction, SR release CaSR release Ca2+2+
intointo
cytosol.cytosol.
 CaCa2+2+
will bind to troponin, causes tropomyosinwill bind to troponin, causes tropomyosin
moves away from myosin-binding sites on actinmoves away from myosin-binding sites on actin..
 Once myosin-binding sites are free, theOnce myosin-binding sites are free, the
contraction cycle begin.contraction cycle begin.

4 steps in Contraction Cycle4 steps in Contraction Cycle
1.1. ATP hydrolysisATP hydrolysis
2.2. Attachment of myosin to actin to formAttachment of myosin to actin to form
crossbridges.crossbridges.
3.3. Power strokePower stroke
4.4. Detachment of myosin from actinDetachment of myosin from actin

ATP hydrolysisATP hydrolysis
 Myosin heads hydrolize ATP into ADP andMyosin heads hydrolize ATP into ADP and
Phosphate group.Phosphate group.
 Myosin head become reoriented and energized.Myosin head become reoriented and energized.
 ADP and phosphate group remain in the myosinADP and phosphate group remain in the myosin
heads.heads.

Crossbridges formationCrossbridges formation
 The myosin heads attaches to the myosin-binding siteThe myosin heads attaches to the myosin-binding site
on actin forming crossbridges.on actin forming crossbridges.
 Phosphate group releases from myosin head.Phosphate group releases from myosin head.

Power StrokePower Stroke
 Energy stored in the myosin heads is used to move theEnergy stored in the myosin heads is used to move the
myosin heads, causing the actin (thin filament) slidemyosin heads, causing the actin (thin filament) slide
past the myosin (thick filament) towards M line.past the myosin (thick filament) towards M line.

Detachment of myosin from actinDetachment of myosin from actin
 At the end of power stroke, the crossbridge firmlyAt the end of power stroke, the crossbridge firmly
remain attached to the actin until it binds anotherremain attached to the actin until it binds another
molecule ATP.molecule ATP.
 As ATP bind to the ATP binding site on the myosinAs ATP bind to the ATP binding site on the myosin
head, the myosin head detaches from actin.head, the myosin head detaches from actin.

Sliding Filament MechanismSliding Filament Mechanism

TendonTendon
 A cord of dense regular connective tissueA cord of dense regular connective tissue
 Composed by parallel bundle of collagen fiberComposed by parallel bundle of collagen fiber
 Attach muscles to the periosteum of the boneAttach muscles to the periosteum of the bone
 For exp ; Achilles tendon connect gastrocnemiusFor exp ; Achilles tendon connect gastrocnemius
muscles to the calcaneal bone.muscles to the calcaneal bone.
 Flat and broad tendon called aponeuresis.Flat and broad tendon called aponeuresis.
 For exp ; epicranial aponeuresis (scalp) and bicipitalFor exp ; epicranial aponeuresis (scalp) and bicipital
aponeuresis (cubital fossa)aponeuresis (cubital fossa)

 Have the arrangement of actin and myosin and theHave the arrangement of actin and myosin and the
same bands, zones and Z discs as skeletal muscles.same bands, zones and Z discs as skeletal muscles.
 Unique characteristic – intercalated discsUnique characteristic – intercalated discs
 Intercalated discs – connect the end of cardiac musclesIntercalated discs – connect the end of cardiac muscles
fiber with one anotherfiber with one another
 Contain desmosomes, and gap junction.Contain desmosomes, and gap junction.
 Contain endo and perimysium but lack with epimysium.Contain endo and perimysium but lack with epimysium.
Cardiac MusclesCardiac Muscles

 Contraction rate 10 – 15 times longer thanContraction rate 10 – 15 times longer than
skeletal muscles.skeletal muscles.
 Due to Ca2+ enter the sarcoplasm from SR andDue to Ca2+ enter the sarcoplasm from SR and
interstitial fluid.interstitial fluid.
 Contraction stimulated by its own autorhythmicContraction stimulated by its own autorhythmic
muscles fiber.muscles fiber.
 Mitochondria – larger and numerousMitochondria – larger and numerous
Cardiac MusclesCardiac Muscles

 Activated involuntary = cardiac musclesActivated involuntary = cardiac muscles
 Two types ; visceral and multiunitTwo types ; visceral and multiunit
 Visceral – wall of small arteries and veins, stomach,Visceral – wall of small arteries and veins, stomach,
intestine, uterus and urinary bladder.intestine, uterus and urinary bladder.
 Multinunit – wall of larger arteries, airways to the lungs,Multinunit – wall of larger arteries, airways to the lungs,
arrector pili muscles etcarrector pili muscles etc
 Spindle shaped and nonstriated fiber – smoothSpindle shaped and nonstriated fiber – smooth
appearanceappearance
Smooth MusclesSmooth Muscles

 Consists single, oval, centrally located nucleus.Consists single, oval, centrally located nucleus.
 Sarcoplasm contains both thick and thinSarcoplasm contains both thick and thin
filaments.filaments.
 Lack transverse tubul and small amount of SRLack transverse tubul and small amount of SR
contain Ca2+.contain Ca2+.
 Ca2+ sources fromCa2+ sources from caveolaecaveolae (small pouch like(small pouch like
invagination form plasma membrane)invagination form plasma membrane)
Smooth MusclesSmooth Muscles

Muscular tissues has four special properties that enable itMuscular tissues has four special properties that enable it
to function and contribute to homeostasis:to function and contribute to homeostasis:
1.1.Electrical excitabilityElectrical excitability
2.2.ContractilityContractility
3.3.ExtensibilityExtensibility
4.4.ElasticityElasticity
Properties of Muscular TissueProperties of Muscular Tissue

Electrical ExcitabilityElectrical Excitability
 Ability to respond to certainAbility to respond to certain
stimuli by producing electricalstimuli by producing electrical
signal (action potential orsignal (action potential or
impulses)impulses)

ContractilityContractility
 Ability of muscular tissueAbility of muscular tissue
to contract forcefullyto contract forcefully
when stimulated by actionwhen stimulated by action
potentials.potentials.
 When muscles contract, itWhen muscles contract, it
will generates tensionwill generates tension
(force).(force).

ExtensibilityExtensibility
 Ability of muscular tissue to stretch without being aAbility of muscular tissue to stretch without being a
damaged.damaged.

ElasticityElasticity
 Ability of muscularAbility of muscular
tissue to return to itstissue to return to its
original length andoriginal length and
shape after contractionshape after contraction
or extension.or extension.

Producing body movementProducing body movement
 Contraction of muscles –Contraction of muscles –
movement of the whole of themovement of the whole of the
body (walking, jumping, running)body (walking, jumping, running)
 Localized movement – grasping aLocalized movement – grasping a
pen, nodding the headpen, nodding the head
Function of Muscular TissueFunction of Muscular Tissue

Stabilizing body positionStabilizing body position
 Contraction of skeletal musclesContraction of skeletal muscles
stabilize joints and help maintainstabilize joints and help maintain
body position ; standing, sittingbody position ; standing, sitting

Storing and moving substancesStoring and moving substances
within the bodywithin the body
 Cardiac muscles contraction –Cardiac muscles contraction –
pumped the blood throughout the bodypumped the blood throughout the body
 Ring shaped smooth muscles –Ring shaped smooth muscles –
sphincter help prevent form back flowsphincter help prevent form back flow
of the foodof the food

Generating heatGenerating heat
 When muscular contractionWhen muscular contraction
occurs, it produces heatoccurs, it produces heat
 This process known asThis process known as
thermogenesisthermogenesis
 Important for maintainImportant for maintain
normal body temperature.normal body temperature.

Macroscopic & Microscopic Structure of Muscular System

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