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Animal TissuesAnimal TissuesTopic 1.4
Epithelial CellNerve Cell
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OBJECTIVESOBJECTIVES
To describe the structure, distributionTo describe the structure, distribution
& functions of Epithelium cells.& functions of Epithelium cells.
To describe the structure, distributionTo describe the structure, distribution
& functions of nerve cells.& functions of nerve cells.
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INTRODUCTIONINTRODUCTION BiologistBiologist classifyclassify animalanimal tissuestissues asas ::
i.i. EpithelialEpithelial tissuetissue
ii.ii. ConnectiveConnective tissuetissue
iii.iii. MuscleMuscle tissuetissueiv.iv. NervousNervous tissuetissue
ClassificationClassification ofof tissuestissues dependsdepends onon theirtheirstructurestructure andand originorigin
EachEach kindkind ofof tissuetissue (and(and subtissue)subtissue) isiscomposedcomposed ofof cellscells withwith characteristicscharacteristicssizes,sizes, shapesshapes andand arrangementsarrangements andand eacheachtypetype ofof tissuetissue isis specializedspecialized toto performperform aa
specificspecific functionfunction oror groupgroup ofof functionsfunctions
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The Characteristics ofThe Characteristics of
Epithelial TissuesEpithelial Tissues EpithelialEpithelial tissuetissue coverscovers thethe wholewhole surfacesurface ofof
thethe bodybody ItIt isis mademade upup ofof cellscells closelyclosely packedpacked andand
rangerange inin oneone oror moremore layerslayers ThisThis tissuetissue isis specializedspecialized toto formform thethe coveringcovering
oror lininglining ofof allall internalinternal andand externalexternal bodybodysurfacessurfaces
EpithelialEpithelial cellscells areare packedpacked tightlytightly together,together,withwith almostalmost nono intercellularintercellular spacesspaces andand onlyonly aasmallsmall amountamount ofof intercellularintercellular substancesubstance
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Characteristics (cont)Characteristics (cont)
EpithelialEpithelial tissue,tissue, regardlessregardless thethe type,type, isisusuallyusually separatedseparated fromfrom thethe underlyingunderlying tissuetissuebyby aa thinthin sheetsheet ofof connectiveconnective tissuetissue::
basementbasement membranemembrane²² TheThe basementbasement membranemembrane providesprovides structuralstructural
supportsupport forfor thethe epitheliumepithelium andand alsoalso bindsbinds totoneighbouringneighbouring structuresstructures
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Epithelial cells are attached toEpithelial cells are attached to
one anotherone another SpecialSpecial devicesdevices (intercellular(intercellular junctions) junctions)
provideprovide structuralstructural integrityintegrity ofof thetheepitheliumepithelium
ThereThere areare severalseveral typestypes ofof cellcell junctions junctions..i.i. AdheringAdhering junctions junctions (or(or desmosomes)desmosomes)
ii.ii. TightTight junctions junctions
iii.iii. GapGap junctions junctions
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AdheringAdhering junctions junctions²² ProvideProvide mechanicalmechanical attachmentattachment
TightTight junctions junctions²² BlockBlock diffusiondiffusion
²² HelpsHelps assureassure adequateadequate separationseparation betweenbetweendifferentdifferent fluidfluid compartmentscompartments
GapGap junctions junctions²² ProvideProvide directdirect intercytoplasmicintercytoplasmic communicationcommunication
betweenbetween joined joined cellscells
²² ThatThat is,is, ionsions oror smallsmall moleculesmolecules cancan passpass throughthroughgapgap junctions junctions directlydirectly fromfrom thethe cytoplasmcytoplasm ofof oneonecellcell intointo thethe cytoplasmcytoplasm ofof anan adjacentadjacent cell,cell, withoutwithoutpassingpassing intointo intercellularintercellular spacespace
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Types of epithelial tissueTypes of epithelial tissue
CanCan bebe divideddivided intointo twotwo groupsgroupsdependingdepending onon thethe numbernumber ofof layerslayers ofof
whichwhich itit composescomposesi.i. EpithelialEpithelial tissuetissue whichwhich isis onlyonly oneone cellcellthickthick isis knownknown asas simplesimple epitheliumepithelium
ii.ii. IfIf itit isis twotwo oror moremore cellscells thickthick suchsuch asasthethe skin,skin, itit isis knownknown asas stratifiedstratifiedepitheliumepithelium
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Types of Epithelial TissuesTypes of Epithelial Tissues
Simple
Epithelial
Tissues
Stratified
Epithelial
Tissues
Pseudostratified
Epithelial
Tissues
Epithelial
Tissues
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Functions of Epithelial TissuesFunctions of Epithelial Tissues
ProtectionProtection²² EpithelialEpithelial cellscells fromfrom thethe skinskin protectprotect underlyingunderlying
tissuetissue fromfrom mechanicalmechanical injury,injury, harmfulharmful chemicals,chemicals,
invadinginvading bacteriabacteria andand fromfrom excessiveexcessive lossloss ofof waterwater SensationSensation
²² SensorySensory stimulistimuli penetratepenetrate specializedspecialized epithelialepithelialcellscells
²² SpecializedSpecialized epithelialepithelial tissuetissue containingcontaining sensorysensorynervenerve endingsendings isis foundfound inin thethe skin,skin, eyes,eyes, ears,ears, nosenoseandand onon thethe tonguetongue
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Papillae
50 µm
Taste bud
Epithelial cells Taste receptor cellTaste pore
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SecretionSecretion²² InIn glands,glands, epithelialepithelial tissuetissue isis specializedspecialized toto
secretesecrete specificspecific chemicalchemical substancessubstances suchsuchasas enzymes,enzymes, hormoneshormones andand lubricatinglubricating fluidsfluids
AbsorptionAbsorption²² CertainCertain epithelialepithelial cellscells lininglining thethe smallsmall
intestineintestine absorbabsorb nutrientsnutrients fromfrom thethedigestiondigestion ofof foodfood
ExcretionExcretion
²² EpithelialEpithelial tissuestissues inin kidneykidney excreteexcrete wastewasteproductsproducts fromfrom thethe bodybody andand reabsorbreabsorbneededneeded materialsmaterials fromfrom thethe urineurine
²² SweatSweat isis alsoalso excretedexcreted fromfrom thethe bodybody bybyepithelialepithelial cellscells inin thethe sweatsweat glandsglands
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Diffusion² Simple epithelium promotes the diffusion of gases,
liquids and² Because they form a thin lining, they are ideal for
the diffusion of gases (eg: walls of capillaries andlungs)
Cleaning² Ciliated epithelium assists in removing dustparticles and foreign bodies which have enteredthe air passages
Reduces friction² The smooth, tightly interlocking, epithelial cellsthat line the entire circulatory system reducefriction between the blood and the walls of theblood vessels
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Simple Epithelial TissuesSimple Epithelial Tissues--can be subdivided according to the shapecan be subdivided according to the shape
of its cellsof its cells
Simple squamousSimple squamousepithelial tissues.epithelial tissues.
Simple cuboidalSimple cuboidalepithelial tissues.epithelial tissues.
Simple columnarSimple columnar
epithelial tissues.epithelial tissues.
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Simple Squamous EpitheliumSimple Squamous Epithelium
SquamousSquamous cellscells consistsconsists ofof aa single,single, veryvery thinthinlayerlayer flattenedflattened cellscells
ViewView fromfrom thethe surface,surface, theythey areare polygonalpolygonal--shapeshape
SquamousSquamous cellscells havehave horizontalhorizontal flattened,flattened,ellipticalelliptical nucleinuclei becausebecause ofof thethe thinthin flattenedflattenedformform ofof thethe cellcell
Simplesquamousepithelialtissue offrog skin
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LocationsLocations::²² CapillaryCapillary walls,walls, alveolialveoli ofof thethe lungs,lungs, coveringcovering
visceralvisceral organs,organs, lininglining bodybody cavities,cavities,glomerulusglomerulus ofof thethe kidneykidney
FunctionsFunctions::
²² DiffusionDiffusion andand filtrationfiltration
Simple squamous tissue in lung
alveoli
Simple squamous tissue in linethe walls of blood vessels
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Simple Cuboidal EpitheliumSimple Cuboidal Epithelium
CuboidalCuboidal cellscells areare roughlyroughlysquaresquare oror cuboidalcuboidal inin shapeshape
EachEach cellcell hashas aa sphericalspherical
nucleusnucleus inin thethe centrecentre CommonlyCommonly encounteredencountered inin
glandularglandular ductsducts CuboidalCuboidal epithelialepithelial cellscells maymay
bebe activeactive oror passive,passive,dependingdepending onon locationlocation andandcellularcellular specializationspecialization
Simplecuboidal
epithelium
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LocationsLocations ::²² LiningLining kidneykidney tubules,tubules, salivarysalivary ducts,ducts,
pancreaticpancreatic ductsducts
FunctionsFunctions ::²² Secretion,Secretion, excretionexcretion andand absorptionabsorption
Cuboidal cells that line kidney·stubule
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Simple Columnar TissueSimple Columnar Tissue
TheThe cellscells areare elongatedelongated andand columncolumn--
shapedshaped
TheThe nucleinuclei areare elongatedelongated andand areare usuallyusuallylocatedlocated nearnear thethe basebase ofof thethe cellscells
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i. Simple columnar epitheliumi. Simple columnar epithelium
with microvilliwith microvilli A cross section through smallintestine.
Since columnar cells arequite thick, they do not
readily allow passivediffusion. These cells use active
transport to move nutrientsthrough them from theintestine to the blood
They have numerousmicrovilli on their apicalsurface area to allow forgreater absorption
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LocationLocation
²² lining of the stomach and intestineslining of the stomach and intestines FunctionFunction
²² absorptionabsorption
Intestinalmicrovili
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ii. Ciliated Columnar Epitheliumii. Ciliated Columnar Epithelium
TheseThese areare simplesimple columnarcolumnar epithelialepithelial cells,cells, butbutinin addition,addition, theythey possesposses finefine hairhair--likelikeoutgrowths,outgrowths, ciliacilia onon theirtheir freefree surfacessurfaces
TheseThese ciliacilia areare capablecapable ofof rapid,rapid, rhythmic,rhythmic,wavelikewavelike beatingsbeatings inin aa certaincertain directiondirection
ThisThis movementmovement ofof thethe ciliacilia causescauses thethe mucus,mucus,whichwhich isis secretedsecreted byby thethe gobletgoblet cells,cells, toto traptrap
inhaledinhaled dirt,dirt, bacteriabacteria andand otherother foreignforeignparticlesparticles andand deliverdeliver themthem toto thethe digestivedigestivesystemsystem
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EpithelialEpithelial tissuestissues lininglining thethe cavitiescavities andandpassagewayspassageways ofof thethe bodybody hashas somesome specializedspecializedmucusmucus--secretingsecreting cellscells calledcalled thethe gobletgoblet cellscells
TheThe mucusmucus lubricateslubricates thesethese surfaces,surfaces, offersoffersprotectionprotection andand facilitatesfacilitates movementmovement ofofmaterialsmaterials
MucusMucus containscontains aa substancesubstance calledcalled mucin,mucin,whichwhich chemicallychemically destroysdestroys invadersinvaders
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GOBLET CELLSGOBLET CELLS
TheThe namename gobletgoblet cellcell derivesderivesfromfrom thethe characteristiccharacteristicshapeshape ofof thesethese cellscells
TheirTheir nucleusnucleus isis atat thethe basebaseofof thethe cell,cell, alongalong withwithorganellesorganelles suchsuch asasmitochondria,mitochondria, endoplasmicendoplasmicreticulumreticulum andand GolgiGolgi..
TheThe remainderremainder ofof thethe cellcell isisfilledfilled withwith membranemembrane--boundboundsecretorysecretory granulesgranules filledfilledwithwith mucusmucus..
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LocationLocation²² Usually found in the air passages like noseUsually found in the air passages like nose
²² Also found in the uterus and Fallopian tubesAlso found in the uterus and Fallopian tubesof femalesof females
FunctionFunction²² In the female reproductive system, theIn the female reproductive system, the
movement of cilia propel the ovum to themovement of cilia propel the ovum to theuterusuterus
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TheTheOviductOviduct
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STRATIFIED EPITHELIAL
TISSUES
� Where body lining have to withstand wear andtear, the epithelia are composed of severallayers of cells and are called compound orstratified epithelium
1. Stratified squamous epithelium2. Stratified cuboidal epithelium3. Stratified columnar epithelium4. Transitional epithelium
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Stratified Squamous EpitheliumStratified Squamous Epithelium
ConsistsConsists ofof flattenedflattened cellscells onon thethe surfacesurfaceoverlyingoverlying multiplemultiple layerslayers ofof cellscells thatthat usuallyusuallyareare moremore cuboidalcuboidal oror columnarcolumnar towardtoward thethebasebase ofof thethe epitheliumepithelium
� The lower cells (basal cells) aremitotically active and replace thecells of the epithelium which are
lost by wear and tear.� Division of lower cells causesolder one to be pushed upwardtowards the surface, becoming
flattened as they moved.
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StratifiedStratified squamoussquamous epitheliumepithelium isis usuallyusuallyprotectiveprotective
TheThe multiplemultiple layerslayers areare tootoo thickthick forfor efficientefficienttransporttransport ofof materialsmaterials OuterOuter layerslayers maymay bebe keratinizedkeratinized (dead(dead andand
hardened)hardened) onon drydry surfacessurfaces suchsuch asas skinskin
KeratinizationKeratinization providesprovides extraextra protectionprotectionagainstagainst abrasionabrasion andand dessicationdessication
The epidermis and dermis ofa frog
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Alternatively,Alternatively, outerouter layerlayer maymay bebe nonnon--
keratinizedkeratinized onon wet,wet, mucousmucous surfaces,surfaces, suchsuch asasthethe corneacornea ofof thethe eyeeye oror thethe lininglining ofof thetheupperupper gastrointestinalgastrointestinal tracttract (eg(eg :: cheekcheek andandesophagus)esophagus)
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Stratified Columnar EpitheliumStratified Columnar Epithelium
StratifiedStratified ColumnarColumnarepitheliumepithelium isis rarerare..
OneOne placeplace you you cancan
findfind itit isis inin thethelargestlargest ductsducts ofofsalivarysalivary glandsglands
TheThe basalbasal layerlayer ofof
cellscells areare cuboidalcuboidalcellscells andand thethe layerlayernearestnearest thethe apicalapicalsurfacesurface includesincludescolumnarcolumnar cellscells
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Notice how the bottomNotice how the bottomlayer (Red Line), lookslayer (Red Line), lookscuboidal in nature butcuboidal in nature butthe because the topthe because the toplayer is columnar, and itlayer is columnar, and itis the top layer whichis the top layer whichdetermines thedetermines theclassificationclassification, this is, this is
called stratifiedcalled stratifiedcolumnar.columnar.
Green lineGreen line -- Top layerTop layer
Red LineRed Line -- Bottom layerBottom layer
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Stratified Cuboidal EpitheliumStratified Cuboidal Epithelium
SweatSweat glandgland ductsductsareare examplesexamples ofofstratifiedstratified cuboidalcuboidal
epithelium,epithelium, usuallyusuallyhoweverhowever therethere areareonlyonly twotwo layerslayers ofofcellscells
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This is an image of aThis is an image of aduct from a sweatduct from a sweatgland.gland.
These ducts areThese ducts arelined withlined with StratifiedStratifiedCuboidal EpitheliumCuboidal Epitheliumindicated by theindicated by the
yellow arrows. yellow arrows.
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Pseudostratified & TransitionalPseudostratified & TransitionalEpitheliaEpithelia
TheseThese twotwo typestypes ofof epitheliaepithelia arearedifficultdifficult toto classifyclassify usingusing thethe shapeshape ofof
thethe cellscells inin thethe surfacesurface layerlayer andand thethenumbernumber ofof thethe cellcell layerslayers asas criteriacriteria
Pseudostratified
epithelium
Transitional
epithelium
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Transitional EpitheliumTransitional Epithelium
TransitionalTransitional epitheliumepithelium isis foundfoundexclusivelyexclusively inin thethe excretoryexcretory urinaryurinarypassagespassages (pelvis,(pelvis, ureter,ureter, urinaryurinary bladderbladderandand partpart ofof thethe urethra)urethra)
TheThe namename ´transitionalµ´transitionalµ derivesderives fromfromthisthis tissue·stissue·s abilityability toto changechange itsits shapeshape
fromfrom cuboidalcuboidal toto squamoussquamous whenwhenstretchedstretched
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TransitionalTransitional epitheliumepithelium isis designeddesigned toto distenddistendandand returnreturn toto itsits normalnormal size,size, asas itit doesdoes inin thethelininglining ofof thethe urinaryurinary bladderbladder..
ThisThis designdesign providesprovides distensibilitydistensibility andand keepskeepsurineurine fromfrom diffusingdiffusing backback intointo thethe internalinternal
cavitycavity..
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The white line is defining theThe white line is defining thelength of the epithelium.length of the epithelium.
Notice how the cells lookNotice how the cells lookdifferent at the top than thedifferent at the top than thebottom.bottom.
The arrangement makesThe arrangement makessense functionally because bysense functionally because bythe top most layer beingthe top most layer beingplump (orange arrow), allowsplump (orange arrow), allowsthem to be compressed whenthem to be compressed whenthe bladder is full.the bladder is full.
HINT: If the top cells areHINT: If the top cells are
plump, the bladder or lumenplump, the bladder or lumenis empty. If they are flat, itis empty. If they are flat, itis full.is full.
White lineWhite line-- defines height ofdefines height ofepitheliumepithelium
Orange ArrowOrange Arrow -- "plump" cell"plump" cell
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Now this is the same type ofNow this is the same type ofepithelium, but look howepithelium, but look howdifferent it looks now.different it looks now.
You almost want to call thisYou almost want to call thisstratified squamous.stratified squamous.
But because of the fact that
But because of the fact thatthis bladder or lumen is fullthis bladder or lumen is full
the plump cells are nowthe plump cells are nowflattened (orange arrow).flattened (orange arrow).
This flattening allows forThis flattening allows fordistention of the bladder todistention of the bladder tohold your urine so you don'thold your urine so you don't
have to go to the bathroomhave to go to the bathroomevery five minutes.every five minutes. White lineWhite line -- Height ofHeight of
epitheliumepithelium Orange arrowOrange arrow -- FlattenedFlattened
"plump" cells"plump" cells
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Pseudostratified columnarPseudostratified columnarepitheliumepithelium
EpitheliumEpithelium consistsconsists onlyonly oneonelayerlayer ofof cellscells withwith allall thethe cellscellsattachattach atat thethe oneone endend toto thethebasementbasement membranemembrane
NotNot allall cellscells havehave aa freefree surfacesurface
NucleiNuclei ofof cellscells areare foundfound atat thethe
differentdifferent levelslevels givinggiving aastratifiedstratified appearanceappearance
ApicalApical surfacesurface maymay havehave ciliacilia
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Glandular EpitheliumGlandular Epithelium
GlandularGlandular epitheliumepithelium formsforms glandsglands
GlandsGlands secretesecrete thingsthings andand areare classifiedclassified
asas endocrineendocrine oror exocrineexocrine..²² EndocrineEndocrine glandsglands secretesecrete thingsthings intointo thethebloodstream,bloodstream, likelike hormoneshormones..
²² ExocrineExocrine glandsglands secretesecrete thingsthings thatthat gogo
outsideoutside ofof thethe body,body, likelike mucusmucus andand sweatsweat
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Exocrine GlandsExocrine Glands
InIn exocrineexocrine glands,glands, thethe connectionconnection betweenbetweenthethe glandgland andand thethe epithelialepithelial membranemembrane isismaintainedmaintained asas aa ductduct
TheThe ductduct channelschannels thethe productproduct ofof thethe glandgland totothethe surfacesurface ofof thethe epithelialepithelial membranemembrane andandthusthus toto thethe externalexternal environmentenvironment
EgEg:: MammaryMammary glands,glands, sweatsweat glands,glands, sebaceoussebaceous
(oil(oil glands)glands)
Fig. 60.26
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Endocrine GlandsEndocrine Glands
EndocrineEndocrine glandsglands areare ductlessductless glandsglands TheirTheir connectionsconnections withwith thethe epitheliumepithelium fromfrom
whichwhich theythey werewere derivedderived areare lostlost duringduring
developmentdevelopment Therefore,Therefore, theirtheir secretions,secretions, calledcalled hormones,hormones,
areare notnot channelchannel ontoonto anan epithelialepithelial membranemembrane Instead,Instead, hormoneshormones enterenter bloodblood capillariescapillaries andand
thusthus staystay withinwithin thethe bodybody EgEg :: AdrenalAdrenal glands,glands, pituitarypituitary glandsglands etcetc
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ConclusionsConclusions
FunctionsFunctions correlatescorrelates withwith structurestructure inin thethetissuestissues ofof animalsanimals
EpithelialEpithelial tissuetissue coverscovers thethe outsideoutside ofof thethe
bodybody andand lineslines internalinternal organsorgans andand cavitiescavities SomeSome epithelialepithelial areare specializedspecialized forfor absorptionabsorption
andand secretionsecretion
TheThe mucusmucus secretedsecreted byby thethe mucusmucus membranesmembraneslininglining thethe digestivedigestive andand respiratoryrespiratory tractstractslubricateslubricates andand moistensmoistens thesethese surfacessurfaces
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NERVE TISSUENERVE TISSUE
?
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NERVOUS TISSUENERVOUS TISSUE
NEURONS- Receiving andtransmitting
signals
GLIA
LCE
LLS
- Support andnourish the
neurons
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NEURONES
SENSORY NEURONES(AFFERENT NEURONES)
INTERNEURONES
MOT OR NEURONES(EFFERENT NEURONES)
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SENSORY NEURONESSENSORY NEURONES
TransmitTransmit nervenerveimpulsesimpulses fromfromreseptors/reseptors/ sensorysensoryorgansorgans toto thethecentralcentral nervousnervoussystemssystems (CNS)(CNS)..
TypicalTypical locationlocation::Eyes,Eyes, earsears;; surfacesurfaceofof skinskin..
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INTERNEURONESINTERNEURONES
TheseThese areare foundfoundwithinwithin thethe brainbrain &&spinalspinal cordcord..
ConnectConnect oneone neuroneneuronetoto anotheranother neuroneneurone &&frequentlyfrequently connectsconnectsaa sensorysensory neuroneneurone totoaa motormotor neuroneneurone..
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MOTOR NEURONESMOTOR NEURONES
TransmitTransmit nervenerveimpulsesimpulses fromfrom thethecentralcentral nervousnervoussystemsystem toto thethe motormotororgansorgans oror effectors,effectors,usuallyusually musclemuscle ororglandsglands..
TypicalTypical locationlocation::BrainBrain && spinalspinal cordcord
Fig. 54.2
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STRUCT URE OF ASTRUCT URE OF A
NEURONENEURONE
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The structural and functional unit ofthe nervous system is the neuron ornerve cell
Nerve impulses are conducted along a neuron.
² Dentrite p cell body p axon hillock paxon
² Some axons are insulated by a myelin
sheath.
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CELL BOD YCELL BOD Y
ConsistConsist ofof aa nucleusnucleus && cytoplasmcytoplasm..
TheThe cytoplasmcytoplasm containscontains manymany organelles,organelles, suchsuch asasmitochondriamitochondria && Nissl·sNissl·s granulesgranules..
Nissl·sNissl·s granulesgranules consistconsist ofof ERER && polyribosomespolyribosomes.. TheThe cellcell bodybody hashas aa numbernumber ofof dendronsdendrons && finerfiner
branchesbranches calledcalled dendritesdendrites..
DendritesDendrites conductconduct impulsesimpulses towardstowards thethe cellcellbodybody..
TheThe cellcell bodybody integratesintegrates incomingincoming signalssignals
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AXONAXON
AlthoughAlthough microscopicmicroscopic inin diameter,diameter, anan axonaxonmaymay bebe 11 mm oror moremore inin lengthlength andand maymay divide,divide,formingforming branchesbranches calledcalled axonaxon collateralscollaterals
TheThe axonaxon conductsconducts nervenerve impulsesimpulses awayaway fromfromthethe cellcell bodybody toto anotheranother neuronneuron oror toto aa musclemuscleoror glandgland
AtAt itsits endend thethe axonaxon divides,divides, formingforming manymanyterminalterminal branchesbranches thatthat endend inin synapticsynapticterminalsterminals
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TheThe synapticsynaptic terminalterminal releasereleaseneurotransmitter,neurotransmitter, chemicalschemicals thatthat transmittransmitsignalssignals fromfrom oneone neuronneuron toto anotheranother oror fromfrom
neuronneuron toto effectoreffector TheThe junction junction betweenbetween aa synapticsynaptic terminalterminal andand
anotheranother neuronneuron isis calledcalled aa synapsesynapse (a(a smallsmallspacespace existexist betweenbetween thethe membranesmembranes ofof thesethese
twotwo cells)cells)
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MYELIN SHEATHMYELIN SHEATH
In vertebrates, the axons of many neuronsoutside the CNS are surrounded by a seriesof Schwann cells that form an insulatingcovering, the myelin sheath
Gaps in the myelin sheath, called nodes ofRanvier, occur between successive Schwanncells
ManyMany nonnon--vertebratevertebrate animalanimal suchsuch asas annelids,annelids,arthropodsarthropods && molluscsmolluscs havehave nonnon--myelinatedmyelinatedgiantgiant axonsaxons toto speedspeed upup thethe raterate ofofconductionconduction ofof nervenerve impulsesimpulses..
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AA nervenerve consistsconsists ofof hundredshundreds oror eveneventhousandsthousands ofof axonsaxons wrappedwrapped togethertogether ininconnectiveconnective tissuetissue
nerve·s outerwrapping bloodvessels
nervefascicle
axon
myelin sheath
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GLIAL CELLSGLIAL CELLS GlialGlial cellscells (supporting(supporting cells)cells) collectivelycollectively
makemake upup thethe neuroglianeuroglia (literally,(literally, nervenerve glue)glue) GlialGlial cellscells outnumberoutnumber neuronsneurons tenfoldtenfold toto
fiftyfoldfiftyfold TheThe functionfunction isis toto provideprovide structuralstructural
supportsupport andand supplysupply metabolitesmetabolites toto thetheneuronsneurons
ThreeThree typestypes ofof glialglial cellscells inin thethe CNSCNS ::
i.i. MicrogliaMicrogliaii.ii. AstrocytesAstrocytesiii.iii. OligodendrocytesOligodendrocytes
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Neurons
Dendrite
Nucleiof
glialcells
Axon
100 µm
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ConclusionsConclusions
Neurons,Neurons, thethe functionalfunctional unitsunits ofof nervousnervoustissue,tissue, areare composedcomposed ofof aa cellcell bodybody withwithextendingextending dendritesdendrites andand axonsaxons thatthat
transmittransmit electricalelectrical signalssignals calledcalledimpulsesimpulses