Epithelium Nerve 3

8/6/2019 Epithelium Nerve 3

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Animal TissuesAnimal TissuesTopic 1.4

Epithelial CellNerve Cell



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.



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



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



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



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



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



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



Types of Epithelial TissuesTypes of Epithelial Tissues

Simple

Epithelial

Tissues

Stratified

Epithelial

Tissues

Pseudostratified

Epithelial

Tissues

Epithelial

Tissues



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



Papillae

50 µm

Taste bud

Epithelial cells Taste receptor cellTaste pore



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



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



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.



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



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



Fig. 52.7



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



LocationsLocations ::²² LiningLining kidneykidney tubules,tubules, salivarysalivary ducts,ducts,

pancreaticpancreatic ductsducts

FunctionsFunctions ::²² Secretion,Secretion, excretionexcretion andand absorptionabsorption

Cuboidal cells that line kidney·stubule



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



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



LocationLocation

²² lining of the stomach and intestineslining of the stomach and intestines FunctionFunction

²² absorptionabsorption

Intestinalmicrovili



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



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



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..



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



TheTheOviductOviduct



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



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.



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



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)



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



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



Stratified Cuboidal EpitheliumStratified Cuboidal Epithelium

SweatSweat glandgland ductsductsareare examplesexamples ofofstratifiedstratified cuboidalcuboidal

epithelium,epithelium, usuallyusuallyhoweverhowever therethere areareonlyonly twotwo layerslayers ofofcellscells



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.



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



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



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..



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



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



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



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



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



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



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



NERVE TISSUENERVE TISSUE

?



NERVOUS TISSUENERVOUS TISSUE

NEURONS- Receiving andtransmitting

signals

GLIA

LCE

LLS

- Support andnourish the

neurons



NEURONES

SENSORY NEURONES(AFFERENT NEURONES)

INTERNEURONES

MOT OR NEURONES(EFFERENT NEURONES)



SENSORY NEURONESSENSORY NEURONES

TransmitTransmit nervenerveimpulsesimpulses fromfromreseptors/reseptors/ sensorysensoryorgansorgans toto thethecentralcentral nervousnervoussystemssystems (CNS)(CNS)..

TypicalTypical locationlocation::Eyes,Eyes, earsears;; surfacesurfaceofof skinskin..



INTERNEURONESINTERNEURONES

TheseThese areare foundfoundwithinwithin thethe brainbrain &&spinalspinal cordcord..

ConnectConnect oneone neuroneneuronetoto anotheranother neuroneneurone &&frequentlyfrequently connectsconnectsaa sensorysensory neuroneneurone totoaa motormotor neuroneneurone..



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



STRUCT URE OF ASTRUCT URE OF A

NEURONENEURONE



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.



Fig. 54.4



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



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



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)



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..



AA nervenerve consistsconsists ofof hundredshundreds oror eveneventhousandsthousands ofof axonsaxons wrappedwrapped togethertogether ininconnectiveconnective tissuetissue

nerve·s outerwrapping bloodvessels

nervefascicle

axon

myelin sheath



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



Neurons

Dendrite

Nucleiof

glialcells

Axon

100 µm



ConclusionsConclusions

Neurons,Neurons, thethe functionalfunctional unitsunits ofof nervousnervoustissue,tissue, areare composedcomposed ofof aa cellcell bodybody withwithextendingextending dendritesdendrites andand axonsaxons thatthat

transmittransmit electricalelectrical signalssignals calledcalledimpulsesimpulses



THAT·S ALLTHAT·S ALLFOR TODAYFOR TODAY

Epithelium Nerve 3

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