Organes visuels

Introductionauxorganesvisuels

Thevisualorgansarethereceptorsforhumansandanimalstoperceiveexternalthingsthroughtheactionoflight.Lightactsonthevisualorganstoexcitethesensorycells, andtheinformationisprocessedbythevisualnervoussystemtoproducevision.Throughvision, humansandanimalsperceivethesize, la luminosité, la couleur, movementandstaticofexternalobjects, andobtainvariousinformationthatisimportanttothesurvivalofthebody.Atleast80% ofexternalinformationisobtainedthroughvision.Visionisthemostimportantthingforhumansandanimals.feel.Thevisualsystemofvertebratesusuallyincludestheretina, relatednervepathwaysandnervecenters, aswellasvariousaccessorysystemsnecessaryforitsfunctions.

Systèmes auxiliaires

Ces systèmes auxiliaires comprennent principalement : les muscles extra-oculaires, qui peuvent faire bouger le globe oculaire dans toutes les directions ; le système réfractif de l'œil (cornée, cristallin, etc.), qui garantit les objets externes.

Composition d'organes

Composition

Theperipheralsensoryorganthatcausesvisionistheeye.Thevisualorganconsistsoftheretinacontainingphotoreceptorcellsandtherefractivesystemasanaccessorystructure.composition.Thesuitablestimulusforthehumaneyeiselectromagneticwaveswithawavelengthof380-780nm; inthisvisiblespectrum, thehumanbraincandistinguishthedifferentbrightnessandcoloroftheretinaimagebyreceivingincominginformationfromtheretina, sothatthelightinthefieldofviewcanbeseenclearlyTheoutline, la forme, la couleur, la taille, distanceandsurfacedetailsofthereflectivematerialoftheobject.Variousobjectsinnature, caractères, graphicsandotherimagesarereflectedinthehumanbrainthroughthevisualsystem.About95% ofalltheinformationobtainedbythehumanbraincomesfromthevisualsystem, sotheeyeisundoubtedlyoneofthemostimportantsensoryorgansinthehumanbody.

Structure fonctionnelle

Inadditiontotheextraocularmusclesthatcontroleyemovement, thesclera, choroidandotherstructuresthatplayaroleinmaintenanceandnutrition, theeyeisdirectlyrelatedtotheproductionofvisualafferentinformationThefunctionalstructureistherefractivesystemlocatedonthemidlineoftheeyeballandtheretinalocatedatthebackoftheeyeball.Fromthecornea, theaqueoushumor, thelens, thevitreousbodytothefrontsurfaceoftheretina, therearesometransparentandnon-vascularizedtissues.Theyconstitutetherefractivesystemintheeye, whichrefractsthelightfromoutsidetheeye, andfinallytheimageisimagedontheretina.Theretinahasacomplexstructuresimilartonervetissue, whichcontainsrodsandconesthatarehighlysensitivetolightstimuli, whichcanconvertthevisualinformationcontainedinexternallightstimuliintoelectricalsignals, andperformpreliminaryprocessingintheretina.Itistransmittedtothebrainintheformofactionpotentialsofopticnervefibers.Therefore, todescribethefunctionoftheeye, wemustfirststudytheunlearnedcharacteristicsoftheintraocularrefractivesystem, andfigure commentilspeuventimagerdesobjetsàdifférentesdistancessurlarétineetleslimitesdeformerdesimagesd'objetsclaires;deuxièmement,ilestnécessairedeclarifiercommentlarétine effectue l'imagerierétinienne.Transformationetcodage.

Système périphérique

Theeyeandretinaaresphericalinshape, surroundedbysclera.Thescleraisinfrontofthetransparentcornea.Behindthecorneaisthelens, whichisequivalenttothelensofacameraandisthemainrefractivesystemoftheeye.Theanteriorandposteriorchambersbetweenthelensandthecorneacontainaqueoushumor.Theentireeyeballbehindthelensisfilledwithagel-likevitreousbody, whichcanprovidenutrientstovarioustissuesoftheeyeandhelpmaintaintheshapeoftheeyeball.Ontheinnersurfaceoftheeyeball, thereisalayerofretinawithathicknessofonly0.3mm, whichistheperipheralpartoftheopticnervoussystem.Betweentheretinaandthescleraisthechoroidfullofbloodvessels, whichnourishestheretina.

Thecorneaandlensformtherefractivesystemoftheeye, whichmakesexternalobjectsformaninvertedimageontheretina.Thecurvatureofthecorneaisfixed, butthecurvatureofthelenscanbeadjustedbytheciliarymuscleviathesuspensoryligament.Whentheobservationdistancechanges, thefocallengthoftheentirerefractivesystemischangedthroughthechangeofthelenscurvature, soastoensurethattheexternalobjectsareclearlyimagedontheretina.Thisfunctioniscalledvisualadjustment.Whenthevisualaccommodationisabnormal, theobjectcannotbeclearlyimagedontheretina, andnearsightednessorhyperopiacanoccur.Atthistime, asuitablelensisneededtocorrectit.Betweenthecorneaandthelens, thepupilformedbytheirisactsasadiaphragm.Thepupilshrinkswhenilluminatedandexpandsinthedarktoadjusttheamountoflightenteringtheeye, whichalsohelpstoimprovetheimagingqualityoftherefractivesystem.Pupilandvisualadjustmentarecontrolledbytheautonomicnervoussystem.

Le mouvement du globe oculaire est réalisé par les six muscles extra-oculaires.

Il contient une couche de tissu nerveux contenant des centaines de millions de cellules nerveuses. Selon les caractéristiques de la forme et de l'emplacement de ces cellules, il peut être divisé en six catégories, à savoir les photorécepteurs, les cellules horizontales, les cellules bipolaires et les cellules macrines.

Classésparforme

Photoreceptorscanbedividedintotwocategoriesaccordingtotheirshapes, namelyrodcellsandconecells.Thephotoreceptorsintheretinaofnocturnalanimals (suchasmice) aredominatedbyrodcells, whilethedaytimeanimals (. Suchaschickens, écureuils, etc) aredominatedbyconecells.Butmostvertebrates (includinghumans) haveboth.Inthehumanretina, thereareabout6to8millioncones, andthetotalnumberofrodsreachesmorethan100million.Theyappeartobedistributedintheretinaintheformofmosaics; theirdistributionisuneven.Inthefoveaareaof themaculaoftheretina, therearealmostonlycones.Thisareahashighspatialresolution (visualacuity, alsocalledvision) .Il a également une bonne vision des couleurs, qui est la plus importante pour la vision. Dans la zone en dehors de la fovéa, il existe les deux types de cellules.

Theneuralnetworkoftheretinaanditsinformationprocessing.Hundredsofmillionsofnervecellsintheretinaarearrangedin3layers, formingacomplexnetworkofinformationprocessingthroughsynapses, namelyphotoreceptorsandbipolarcells, andsynapsesbetweenhorizontalcells.Theouterreticularlayercomposedofbipolarcells, amacrinecells, andtheinnerreticularlayercomposedofsynapsesbetweenganglioncells.Afterthephotoreceptorsareexcited, theirsignalsaremainlytransmittedtotheganglioncellsthroughthebipolarcells, andthentothenervecenterthroughtheaxons (opticalnervefibers) ofthelatter.Butintheouterreticularlayerandtheinnerreticularlayer, thesignalismodulatedbyhorizontalcellsandamacrinecells.Thetransmissionofthissignalismainlyachievedthroughchemicalsynapses, buttherearealsoelectricalsynapses (gapjunctions) betweenphotoreceptorsandhorizontalcells, linkingtheinteractionswitheachother.

Thetransmissionpathwaysoftherodcellsignalandtheconecellsignalintheretinaarerelativelyindependent, untiltheganglioncellsconverge.Intheouterreticularlayer, horizontalcellsreceivesignalsfromphotoreceptorsinawiderangeandinteractwithbipolarcellsatsynapses.Inaddition, thehorizontalcellsalsomodulatethesignalintheformoffeedbacktothephotoreceptors.Thesignalsfromthebipolarcellsintheinnerreticularlayeraretransmittedtotheganglioncells, andtheamacrinecellsconnecttheneighboringbipolarcells.Theconfluenceofrodandconesignalsmayalsooccurinamacrinecells.Thesignalofthephotoreceptorismainlytransmittedtotheinterneuronsbychangingtheamountofthetransmitterreleasedbythechemicalsynapse.

TraitementdesinformationsducentrevisuelLesinformationstraitéesparleréseauneuralrétiniensonttransmisesaucentreparlesaxonesdescellulesganglionnaires-fibresnerveuxoptiques.

En raison de l'intersectiondunerfoptique,lecorpsgéniculélatéralgaucheetlecortexsontreliésauxdeuxmoitiésgauchedelarétine,doncilssontrelatifsàlamoitiédroiteduchampvisuel;lecorpsgéniculélatéraldroitetlecortexdroitLa situationestopposée.

L'information visuelle subit un traitement supplémentaire à tous les niveaux de la voie centrale visuelle.

Système de réfraction

Le systèmefractif de l'œil et son ajustement

Lorsque la lumière entre dans le corps réfractif sphérique unique composé d'un autre milieu thermique à partir de l'air, elle entre dans le matériau.

F2iscalledtherearmainfocallengthorthesecondfocallength (thefocallengthontheairsideisthefrontmainfocallengthorthefirstfocallength), whichreferstothedistancefromtherefractionsurfacetotherearmainfocalpoint, andcanrepresenttherefractivepowerofthisrefraction.Anothermethodcanbeusedtoexpresstherefractivepowerofarefractingbody, thatis, themainfocallengthisexpressedinm (mètres), andthenthereciprocalofthisvalueistaken.Thelatteriscalledthediopteroftherefractingbody, Themainfocallengthofacertainlensis10cm, whichisequivalentto0.1m, andtherefractivepowerofthelensis10powers (10D) .Itisusuallystipulatedthatthepowerofaconvexlensisapositivevalue, andthepowerofaconcavelensisanegativevalue.

Lalongueurinfocaleprincipaleestleparamètreoptiqueleplusimportantducorpsfringant,à partir duquellapositiondel'imageréfractéeforméeparunobjetàn'importe quellepositionpeutêtrecalculée.Prenantuneobjectifcommeexemple,siladistancedel'objetαestconnue,ladistanceimagebpeutêtrecalculéeparlaformulesuivante :

1/a+1/b=1/F2(2)

Itcanbeseenfromequation (2) thatwhentheobjectdistanceatendstoinfinity, 1 / aapproacheszero, SO1 / biscloseto1 / F2, thatis, theimagedistancebisalmostequaltoF2; thisisInotherwords, whenanobjectisinfinitelyfarawayfromaconvexlens, itsimagingpositionwillbeatthebackmainfocusposition.Itisalsonotdifficulttoseethatforobjectswhoseobjectdistanceislessthaninfinity, theirimagedistancebisalwaysgreaterthanF2, thatis, theywillbeimagedfartherthanthemainfocus.Theabovetwoconclusionsareveryimportantforunderstandingtherefractiveimagingabilityoftheeye.

Enoutre, accordingtotheprincipleofoptics, thepositionofthemainfocusisthepositionwheretheparallellightraysarecondensedintoapointafterbeingrefracted.Thisconclusionisconsistentwiththefirstconclusionmentionedabove.Thesurfaceofeachobjectcanbeconsideredtobecomposedofcountlessluminouspointsorreflectivepoints, andthelightemittedbyeachpointisdivergent, onlywhenthedistancebetweenthesepointsandthecorrespondingrefractingsurfacetendstobeinfinite, Thelightraysreachingtherefractingsurfacefromthesepointscanbeclosetoparallel, soaftertheyarerefracted, theyconvergeintoapointonthesurfacewherethemainfocusislocated, andtheentiresubstancereachesonesurfacetoformanobjectimage.Ofcourse, theconceptofinfinitepassageitselfdeterminesthatitisanimpossibleposition.Infact, forthehumaneyeandgeneralopticalsystems, thelightfromeachlightpointofanobjectbeyond6mcanberegardedasnearlyparallel.Therefore, itispossibletoformanobjectimageonthesurfacewherethemainfocusislocated.

Caractéristiques optiques du système réfractif de l'œil

Whenusingtheaboveopticalprinciplestoanalyzetherefractivecharacteristicsoftheeye, thefirstdifficultyencounteredisthattheeyeballisnotathinlensorasinglesphericalrefractiveindex.Itisarefractionsystemcomposedofaseriesofrefractionbodieswithdifferentradiiandrefractiveindices.Obviously, thebackmainfocallengthofthehumaneye'srefractivesystemcannotbesimplycalculatedbyequation (1), butitsmostimportantrefractionoccursinthecornea, andmorecomplicatedcalculationsbasedongeometricalprinciplescanstilltracethelightpassingthroughtheeyeThepathofmultiplerefractingsurfaces, andthepositionofthebackmainfocusdeterminedbythesecombinedlensgroupsisobtained.Thecalculationresultsshowthatwhenthenormaladulteyeisinaquietstatewithoutadjustment, thepositionoftherearmainfocusofitsrefractivesystemisexactlythepositionofitsopticwindmembrane.Thisanatomicalrelationshipisveryimportantforunderstandingtherefractiveimagingcapabilitiesofnormaleyes.Itshowsthatallobjectslocated6minfrontoftheeyetoinfinity, accordingtoformula (2) orbecausetheligh temittedorreflectedbythemisalmostparallelwhenreachingtherefractivesystemoftheeye, theycanbeformedontheretinaBasicallyclearimages, justlikethefilmplacedinthemainfocusofthecamera, youcantakeaclearperspective.Ofcourse, thehumaneyedoesnotunconditionallyseeanydistantobjects.Forexample, thehumaneyecanseethemoon (orotherfartherstars) andthelargershadowsonitssurface, butitcannotseethesmallerobjectsonthemoon.Orfeatures.Thereasonforthelatterlimitationisthatifthelightfromanobjectistooweak, ortheyarescatteredorabsorbedwhentheytravelthroughthespacevirgin, thenwhentheyreachtheretina, theyhavebeenweakenedtotheextentthattheyarenotenoughtoexcitethephotoreceptorcells, soitisimpossible.Beperceived; Enoutre, ifobjectsaretoosmallortheirdistancefromtheeyeistoolarge, thesizeoftheirformationontheretinawillbesmallerthanthelimitoftheretina'sresolvingpower, andthereforecannotbesensed.

Ajustement des yeux

Iftherefractivepoweroftheeyeinaquietstateisjusttoimageobjectsbeyond6montheretina, thenthelightfromobjectscloserto6mwillbeofdifferentdegreesTheyareradial, andtheirimagingpositionafterrefractionwillbebehindthemainfocus, thatis, thepositionoftheretina; becausethelightisnotfocusedwhenitreachestheretina, theobjectimageisblurred, whichcanonlycauseablurredvisualimage.However, thenormaleyeisalsoveryclearwhenlookingatthenearobject.Thisisbecausetheeyehasadjusted (logement) whenlookingatthenearobject, sothatthelightenteringtheeyeundergoesstrongrefraction, andasaresult, theimagecanalsobeimagedontheretina.Theadjustmentofthehumaneye, thatis, thechangeinrefractivepower, ismainlydependentonthechangeintheshapeofthelens; thisisaneuroreflexactivity, andtheprocessisasfollows: Whenablurredvisualimageappearsinthevisualcortex, theresultingdownwardimpulseThecortex-midbraintractinthepyramidaltractreachesthemediannucleusofthemidbrain, puis atteint le noyau associé qui envoie les fibres préganglionnaires parasympathiques de l'oculomoteur erve, andfinallyreachestheintraocularciliarymusclethroughtheciliaryganglion, makingitcirculateMusclecontractioncausesthesuspensoryligamentconnectedtothelenscapsuletorelax; thiscausesthelenstoprotrudeforwardandbackwardduetoitsownelasticity (theanteriorprotrusionismoreobvious), whichincreasesthetotalrefractivepoweroftheeyewhenitisquieter.Themoreradiantlightisfocusedinadvanceandcanalsobeimagedontheretina.Indicatesthechangeintheshapeofthelensbeforeandafteradjustment.Obviously, theclosertheobjectistotheeyeball, thegreaterthedegreeofdivergenceofthelightreachingtheeye, whichrequiresthelenstobecomemoreconvex.Whenadjustingthereflex, inadditiontothechangeofthelens, thereisalsotheshrinkageofthepupilandtheconvergenceofthenasalmidlineofthevisualaxisofthetwoeyes.Themeaningoftheformeristoreducetheamountoflightenteringtheeye (whentheobjectmovescloser, strongerlightwillarrive.Eyeball) andreducethesphericalaberrationandchromaticaberrationoftherefractivesystem; themeaningoftheconvergenceofthetwoeyesisthattheimageofthe objetpeuttoujourstombersurlapositionappropriéedelarétinedesdeuxyeuxlorsqu'on regardeunobjet proche.

Réponse à la lumière

L'élève se réfère à l'ouverture au milieu de son iris, qui est le portail de la lumière pour entrer dans l'œil ; il se rétrécit en lumière vive,

Theorganofvision (rightSideeyeballhorizontallybrokenpatternpicture) Scatteredinthedarkplace.Theirisiscomposedofmultipleunitsofsmoothmuscle; aroundthepupilisthecircularmusclelayer, whichisinnervatedbytheparasympatheticnervefibersintheoculomotornerve, whichshrinksthepupilwhencontracted, soitisalsocalledpupillarysphincter; Itisinnervatedbytheascendingsympatheticnervefibersintheneckanddilatesthepupilswhencontracted, soitisalsocalledmydriaticmuscle.Thesizeofthepupilcancontroltheamountoflightenteringtheeye.Thediameterofordinarypeople'spupilscanvarybetween1.5-8.0mm.Assumingthatthepupildiametercanbeincreasedby5timeswhenapersonentersadarkroomfromabrightplace, thepupil'slight-receivingareashouldbeincreasedby25times; visiblepupilchangeshavetheeffectofkeepingtheamountoflightenteringtheeyerelativelyconstantunderdifferentlightingconditions.However, theintensityofthestrongsunlightinthedarkroomisactuallyreducedbyabout1milliontimes, sothechangeofpupilsizealoneisfarfromenoughtokeeptheamountoflightenteringtheeyecons tant.Infact, thehumaneyereliesondifferentphotoreceptorcellsintheretinatoreceivelightstimulationunderdifferentbrightnessconditions.Therodcellsthatworkindarklightaremoresensitivetolightthantheconesthatworkinbrightlight.Thecellsaremuchlarger, sowhenyoulookatsomethinginthedark, youonlyneedtoincreasetheamountoflightenteringtheeye.Itcanbeseenthatitismeaningfultoadjusttheamountoflightenteringtheeyebychangingthepupilsize.Theresponseofpupilsizetochangesinlightintensityisakindofneuralreflex, calledpupilreflextolight.Thereceptorthatcausesthisreflexistheretina, andtheafferentfibersareintheopticnerve, butthispartofthefibersdoesnotreachthelateralgeniculatebodyafterenteringthecenter, andchangesneuronsintheanteriorregionofthemidbrain, andthentotheipsilateralandoppositesides.Onthesideoftheoculomotornucleus, theefferentfibersaremainlytheparasympatheticfibersintheoculomotornerve, andtheeffectorsarealsomainlythepupillarymuscles.

Thecharacteristicofthepupil'sresponsetolightisthebilateralnatureoftheeffect, thatis, ifthelightisononeeye, inadditiontothedilatedpupilsoftheilluminatedeye, thepupilsalsodiminishwhentheyarenotexposedtolight.Iamthereflectionoflightformutualinductance.Inclinicalpractice, abnormalitiessuchasdisappearanceofpupilresponsetolight, disparitybetweenleftandrightpupil, disappearanceofmutualinductivepupilreaction, etc.aresometimesseeninclinicalpractice.Itisoftentheresultofdamagetoacertainpartofthereflectionarcrelatedtothesereflections.Therefore, theabnormalpupilresponsecanbeborrowed.Helpinthelocalizationanddiagnosisofneuropathy.Aqueoushumorandintraocularpressurereferstothefluidthatfillstheanteriorandposteriorchambersoftheeye.Itscompositionissimilartothatofplasma, buttheproteincontentismuchlowerthanthatofplasma, whilethecontentofHCO3-exceedsthatofplasma, par conséquent, thetotalosmoticpressureofaqueoushumorItisalsohigherthanplasma.Aqueoushumorisgeneratedinthechoroidalplexusoftheciliarybody. Après qu'il soit généré, il entre theanteriorchamberfromtheposteriorchamberthroughthepupil, thenentersthescleralvenoussinusfromtheanteriorchamberangleatthejunctionofthescleraandthecornea, andfinallyentersthevenoussystem.Aqueoushumorisconstantlybeinggeneratedandreturningtotheincomevein, makingitflowcontinuouslybetweentheposteriorchamberandtheanteriorchamber.Accordingtothemeasurement, theproductionrateofaqueoushumorisabout2mm3perminuteinnormaltime.Becauseofthedynamicbalancebetweenitsproductionandrecovery, theamountofaqueoushumorintheeyeiskeptconstant, andthevolumeoftheanteriorandposteriorchambersoftheeyeisalsoconstant.Relativelyconstant, sothehydrostaticpressure (thatis, intraocularpressure) alsoremainsrelativelystable.ThenormalvalueofintraocularpressureinChineseadultsis2.27-3.2kPa (17-24mmHg), withanaverageof2.67kPa (17-24mmHg) La stabilité relative de la pression intraoculaire est importante pour maintenir la puissance d'ouverture et de réfraction normale du globe oculaire, en particulier de la cornée. ression, causetheeyeballtodeform, andthecorneacannotmaintainthenormalcurvature.Thetotalrefractivepowerofthehumaneyehasacertainrelationshipwiththeintraocularrefractivebody, butthemostimportantrefractionoccursattheinterfacebetweentheairandthecornea.Thisaccountsforabout80% ofthetotalrefractivepower.Therefore, changesinthecurvatureandshapeofthecorneawillsignificantlyaffecttherefractivepoweroftheeyeandseverelyaffectvision.Aqueoushumoralsoplaysanourishingroleintheavasculartissuesittouches, suchasthecorneaandlens.Aqueouscirculatorydisorderscancauseexcessiveintraocularpressure, whichisclinicallycalledglaucoma, whichcancausemetabolicdisordersofthecornea, lentille, andiris.Inseverecases, itcancausecornealopacityandlossofvision.Themechanismofaqueoushumorformationiscurrentlynotfullyunderstood.

Itisgenerallybelievedthat, exceptforthecapillariesinthechoroidalplexusoftheciliarybody, passivefiltration (similartotheformationoftissuefluidatthearterialendofgeneralcapillaries) allowsthewaterandsaltsintheplasmatopenetratethebloodvesselwallInadditiontotheformationofaqueoushumor, thereareactiveprocessesinvolved, otherwiseitwillbedifficulttoexplainwhyaqueoushumorhashigherconcentrationsofHCO3-andothersaltionsthanthoseinplasma.Itisprovedbyhistochemicalmethodthatciliaryepithelialcellscontainmorecarbonicanhydrase.ThefunctionofthisenzymeistorapidlygenerateCO2andH2OproducedintheprocessofcellmetabolismanddissociateHCO3-, whichpassesthroughthemembrane.Theactivetransportprocessaboveenterstheaqueoushumor, resultinginahighconcentrationintheaqueoushumor.ThenegativepotentialandhighosmoticpressurecausedbythishighconcentrationcanfurtherpromotetheNaandwatermoleculesintheplasmatoentertheaqueoushumor.Clinically, carbonicanhydraseinhibitors (suchasacetazolamide) canbeusedtoreducetheproductionofaqueoushumorandlowerin pression traoculaire.

Système photosensible

Lightfromexternalobjects, throughtherefractivesystemintheeye, formsanimageontheretina, whichisapreconditionforthephotoreceptorcellsintheretinatobestimulated.Theretinalimagealsohasaninternalimageinthephysicalcategory, whichcanbeeasilyexplainedbytheprincipleofgeometricoptics.Itisnotinprincipledifferentfromtheobjectimageformedbyexternalobjectsonthenegativethroughthelensgroupofthecamera, mais thefinal "image" formedbythevisualsysteminsubjectiveconsciousnessisasubjectiveimpressionbelongingtothecategoryofconsciousnessorpsychology, whichisfinallyformedincentralstructuressuchasthecerebralcortexbyneuralinformationfromtheretina.Asthereceptorphysiology, thefocusisonhowtheretinaconvertsphysicalimagesintonervesignalsontheopticnervefibers, andhowthesequenceandcombinationofthesesignalsincludetheimageoftheretina, thatis, theinformationcontentprovidedbyexternalobjects.Itshouldbepointedoutthatalthoughtheprogressofvisualresearchisrelativelyfast, itisonlypreliminary.

Caractéristiques structurelles

Thethicknessoftheretinaisonly0.1-0.5mm, butthestructureisverycomplicated.Themainpartofitcomesfromtheforebrainvesiclesinontogenesis, soitbelongstoaneurologicalstructureinwhichcellsareconnectedtoeachotherthroughsynapses.Classicalhistologydividestheretinaintotenlayers, butaccordingtothemaincelllevel, itissimplifiedtofourlayers.Fromthesideclosetothechoroid, theoutermostlayeroftheretinaisthepigmentcelllayer; thesourceofthislayerisnotneuraltissueThebloodsupplyalsocomesfromthechoroidside, whichisdifferentfromtheotherlayersoftheretinathatreceivebloodsupplyfromtheinnersurfaceoftheretina; clinicallyseenretinaldetachmentoccursbetweenthislayerandotherlayers.Thepigmentcelllayerisnotunimportantforthecauseofvision.ItiscontainedinmelaninparticlesandvitaminA, andithasnourishmentandprotectionforthephotoreceptorcellsadjacenttoit.Theprotectiveeffectisthatinadditiontothepigmentlayerthatcanshieldthescatteredlightfromthesideofthesclera, thepigmentcellscanextendpseudopod-likeprotrusionswhentheretinaisilluminatedbystron glight, andcoattheoutersegmentoftherodcells, makingthemisolatedfromeachotherandlessaffectedbyothersources.Thelightstimulation; onlyunderdarklightconditions, theoutersegmentoftherodisexposed; thisactivityofthepigmentepitheliumiscontrolledbydopaminereceptorsonthemembrane.Theinnersideofthislayeristhephotoreceptorcelllayer.Inhumansandmostmammaliananimals, photoreceptorcellsaredividedintorodsandcones.Theybothcontainspecialphotosensitivepigmentsandaretruephotoreceptorcells.Rodsandconescanbedividedintofourpartsinmorphology, whicharecalledoutersegment, innersegment, cellbody, andendfootfromtheoutsidetotheinside; theoutersegmentisthepartwherethephotosensitivepigmentisconcentrated, whichplaysanimportantroleinthelight-sensitivetransduction.effect.Thedifferenceintheformationofrodsandconesisalsomainlyintheoutersegment.Theyaredifferentinappearanceandcontaindifferentphotosensitivepigments.Theoutersegmentoftherodisalongrod, andtheoutersegmentoftheconeisacone.Bothphotoreceptorcellsaresynapticallyconnectedtothebipol arcellsinthebipolarcelllayerthroughtheendfoot, andthebipolarcellsgenerallycommunicatewiththeganglioncellsintheganglioncelllayer.Inadditiontothislongitudinalcell à cellconnectionintheretina, thereisalsoahorizontalconnection, suchashorizontalcellsbetweenthephotoreceptorcelllayerandthebipolarcelllayer, andamacrinecellsbetweenthelargebipolarcelllayerandtheganglioncelllayer;. Theprotrusionsofthesecellsstretchhorizontallybetweenthetwolayersofcells, whichcantransmitinformationinthehorizontaldirection, makingitpossiblefortheretinatoinfluenceeachotherindifferentareas; theseamacrinecellscanalsodirectlytransmitsignalstotheganglioncells.Inrecentyears, ithasbeendiscoveredthatthereisakindofinterreticularcellintheretina.Itscellbodyislocatedbetweenthebipolarcelllayerandtheganglioncelllayer, buttheprotrusionsextendtothephotoreceptorcelllayerandthebipolarcelllayer.Ifthephotoreceptorcellpassesthroughthebipolarcelltotheganglioncell, itisregardedastheinitialstageofvisualinformation.Inadditiontotheusualchemicalsynaps esintheretina, therearealsoalargenumberofelectricalsynapses.Itcanbeseenthattheretinaisalsothesameasthenervetissue.Therearecomplexconnectionsbetweencellsatalllevels.Aftervisualinformationisinitiallyconvertedintoelectricalsignalsatthephotoreceptorcelllayer, itwillundergosomeprocessinginthecomplexneuralnetworkoftheretina.Andchange, whentheactionpotentialsequenceoftheopticnervefiberistransmittedtothecenterasthefinaloutputsignaloftheretina, theyarealreadypreliminaryprocessedandprocessedinformation.

BlindspotThenerveaxonsemittedfromtheganglioncelllayerfirstaggregateintoabundleonthesurfaceoftheretina, andthenitpenetratestheretinaandprotrudesoutoftheeyeballatthebackoftheeye.Thisformstheopticnerveheadonthesurfaceoftheretina.Intheareaof thenipple, thereisactuallynospecificcellstructureoftheretina, sothelightorthecomponentsoftheretinalimagefallingtherewillnotbeabletobeperceived, soitiscalledablindspot.Theopticnerveheadsonbothsidesareabout3mmfromthenasalsideofthecenterofthemaculaorfoveaintheretina.Butundernormalconditions, theblindspotononesidecanbecompensatedbythecontralateralvisionduetotheuseoftwoeyestoseeobjects, andpeoplearenotawareofanon-visualareaintheirfieldofvision.Theexistenceofblindspotscanbeprovedbyspeciallydesignedmethods.

Accordingtotheresearchonthestructureandfunctionoftheretina, itisbelievedthattherearetwolight-sensitivetransductionsystemsintheretinaofhumansandmostvertebrates.Itiscomposedofrodcellsandtheirassociatedbipolarcellsandganglioncells.Theyarehighlysensitivetolightandcanfeellightstimulationinadimenvironmenttocausevision, buttheyhavenocolorvision.Itcanonlydistinguishbetweenlightanddark; andtherecanonlybearoughoutlinewhenlookingatobjects, andtheaccuracyispoor.Thisiscalledtherodsystemorthelatelightperceptionsystem;. Theotheriscomposedofconecellsandtheirrelatedtransfercells, Theyarelesssensitivetolight, andcanonlybestimulatedunderstronglightregulationssimilartodaylight, buttheycandistinguishcolorswhenlookingatobjects, andtheycanseethedetailsandcontoursoftheobjectsurfaceclearly, withhighresolutionAbility, thisiscalledtheconesystemordaylightsystem (theaforementionedmeasurementofvisualacuityisactuallythemeasurementofthevisualacuityoftheconesystem).

La base principale pour prouver l'existence de ces deux systèmes de transduction photosensible relativement indépendants est :

①Thespatialdistributionofrodsandconesinthehumanretinaisuneven, Theclosertotheperipheryoftheretina, themorerodcellsandthefewerconecells; theclosertothecenteroftheretina, thefewerrodcellsandthemoreconecells; inthecentralfoveaof themacula, allphotoreceptorcellsareopticConewithoutrodcells; Correspondingtotheabove-mentionedcelldistribution, humanvisionischaracterizedbythehighestvisualacuityandcolorvisionofthefoveainbrightlight, andpoorercentralvisioninthedark; onthecontrary, theperipheralpartoftheretinaisCanfeelthestimulationoflowlight, butatthistimethereisnocolorvisionandpoorclarity.

②Whenthetwokindsofphotoreceptorcellsandbipolarcellsandganglioncellsforminformationtransmissionpathways, thereisacertaindegreeofconvergencebetweenlevels, butthisconvergenceisrelativelysmallintheconesystem.Inthefovea, youcanevenseethataconecellisincontactwithonlyonebipolarcell, andthisbipolarcellisonlyincontactwithaganglioncell.Thiskindof withlowornoconvergence "single-lineconnection", Obviouslytheconesystemhasastructuralbasisforhighfineresolution; incontrast, intherodsystem, multiplephotoreceptorcellsarecommonlyassociatedwiththesamebipolarcell, andmultiplebipolarcellsareinthesameganglion.Convergentarrangementofcellconnections; intheperipheryoftheretina, upto250rodcellscanbeseenconvergingintooneganglioncellviaafewbipolarcells; inthiscase, bien entendu, youcannotexpectsuchafeelingThesystemhashighfineresolutioncapability.However, suchapolymerizationsystemhasastrongabilitytosummultipleweakstimuli.

À partir des caractéristiques des systèmes animaux, certains animaux qui se déplacent uniquement à la lumière du jour, tels que les reptiles et les poulets, n'ont pas de tiges dans la rétine, mais uniquement des cellules coniques.

④Les cellules à tiges ne contiennent qu'un seul type de pigment photosensible, à savoir la rhodopsine (rhodopsine), tandis que les cellules à cônes sont différentes en raison des caractéristiques du spectre d'absorption du pigment photosensible qu'elles contiennent.

Mécanisme photosensible

Someonehasextractedacertainpurityofthephotosensitivepigment, rhodopsine, fromtheretina, whichisredinthedark, experimentscanalsoprovethattheextractedTheabsorptionspectrumofthisphotosensitivepigmenttolightofdifferentwavelengthsisbasicallyconsistentwiththesensitivitycurveofnightlightperceptiontodifferentpartsofthespectrum.Thisfactisveryimportant, becausesincetheintensityofthephotochemicaleffectoflightonacertainphotosensitivepigmentisexactlythesameasthevisualintensitycausedbythelight, itisahintthattheformermaybethebasisofthelatter. Thephotochemicalreactionandmetabolismofrhodopsin Themolecularweightofrhodopsinisabout27-28kd.Itisakindofproteinthatbindstoit.Itconsistsofaproteincalledopsinandamoleculecalledopsin.Itiscomposedofthechromophoreof retinal (retnal).Thepeptidechainsequenceofopsinhasbeenclarified,anditspeptidechainhas7segmentsofalpha-helixsegmentsthatpassthroughthemembranestructureandaremainlycomposedofhydrophobicaminoacids,whichhaveasimilarstructuretogeneralcellmembranereceptors.RetinaldehydeisderivedfromvitaminA,whichisanunsaturatedalcoholthatcanbeoxidizedtoretinalundertheactionofanenzymeinthebody.Thepurifiedrhodopsinhasthestrongestabilitytoabsorblightof500nmwavelengthinthesolution.Thisisthesameastheblue-greenlightregion(equivalenttonear500nmwavelength)inthehumaneyeunderlowlightconditions.Green)isconsistentwiththefacts,indicatingthatthehuman scoopia isdirectlyrelatedtothephotochemicalreactionoftherhodopsincontainedintherodcells.Thebrightestareasinthevisualabsorptioncurveofrhodopsinfordifferentpartsofthespe ctrumandthestrongestpartofrhodopsinabsorptionarebothnearthewavelengthof500nm.Rhodopsinisrapidlydecomposedinto opsin andretinalwhenexposedtolight,whichisamulti-stagereaction.Thedecompositionoccursfirstlybecausetheretinalmoleculeundergoesachangeinmolecularconformationwhenilluminated,thatis,itisoriginally11-cis(amorecurvedconformation)intherhodopsinmolecule,butbecomesfullwhenilluminated.Inversion(arelativelystraightmolecularconformation).Thischangeintheconformationoftheretinalmoleculewillresultinachangeintheconformationoftheopsinmolecule.Theactivityofamorecomplexsignaltransmissionsysteminducestheappearanceofreceptorpotentialsintherodcells.Accordingtocalculations,theabsorptionofonelightquantumbyrhodopsinisenoughtochangethemolecularstructureofretinal,resultinginthefinaldecompositionofrhodopsinintoopsinandretinal.Somestagesofrhodopsindecompositionareaccompaniedbythereleaseofenergy,butthisdoesnotseemtobethedirectcauseoftheevokedreceptorpotential.

Rhodopsindecomposedinbrightplacescanbere-synthesizedindarkplaces,thatis,itisareversiblereaction,andtheequilibriumpointofthereactiondependsontheintensityoflight.Thefirststepintheresynthesisofrhodopsinisthatall-transretinalischangedto11-cisretinal,whichwillsoonrecombinewithopsin.Inaddition,thevitaminAstoredinthepigmentcelllayeroftheretinaisalsoall-trans.Theycanalsobecome11-cisunderenergyconsumption,entertherodcells,andthenoxidizeto11-cis.Retinaldehydeisinvolvedinthesynthesisandsupplementationofrhodopsin;however,thisprocessisslowerandisnotanimmediatefactorthatpromotestheresynthesisofrhodopsinsanctions.Whenpeopleseethingsinthedark,theyactuallyhaveboththedecompositionofrhodopsinandthesynthesisofit.Thisisthebasisforpeopletocontinuouslyseethingsinthedark;thedarkerthelight,themoretheprocessoffullbloomexceedstheprocessofdecomposition,theretinaThenumberofrhodopsininthesyntheticstateisalsohigher,whichalsomakestheretinamoresensitivetoweaklight;onthecontrary,whenpeopleareinbrightlight,thedecompositionofrhodopsinisenhanced,andthesynthesisprocessisweak,whichmakestheretinamoresensitive.Muchoftherhodopsinisinadecomposedstate,sothattherodcellsalmostlosetheabilitytosenselightstimulation;humanvisioninbrightlightiscompletedbyanotherphotosensitivesystemthatislesssensitivetolightstimulation,thatis,thecone.Asystemisnotenoughtobestimulatedunderlowlight,andwhentherhodopsinintherodcellsismoredecomposedunderthestronglightsystem,theconesystembecomesthesensorysystemforstronglightstimulationinstead.Intheprocessofrhodopsinandresynthesis,apartofretinalisconsumed,whichultimatelydependsonvitaminAthatentersthebloodcirculationfromfood(aconsiderablepartofitisstoredintheliver)tosupplementit.Long-termintakeof vitaminA willaffectpeople'svisionindarkplacesandcausenightblindness.

Chaoweistructureandproductionofreceptorpotential

Chaoweistructureandproductionofreceptorpotentialintheoutersegmentofrodcells

Theoutersegmentofthephotoreceptorcellisthekeypartforphoto-electricconversion.Theoutersegmentoftherodcellhasaspecialsuperpowerstructure.Intheoutersegment,thereisverylittlecytoplasminthemembrane,andmostofitisoccupiedbysomeneatlyoverlappinglayereddisc-likestructures.Thisdisciscalledtheopticdisc.Eachopticdiscisaflatcapsule.Thestructureofthecapsulemembraneissimilartothatofthecellmembrane.Ithasagenerallipidbilayerstructure,butmostoftheproteinsembeddedinitarerhodopsin,whichiscontainedinrodcells.Infact,almostalloftherhodopsinisconcentratedintheopticdiscmembrane.Thenumberofopticdiscsvariesgreatlyamongrodcellsofdifferentanimals.Therearenearlyathousandofthemintheoutersegmentofeachrodcellinhumans;eachopticdisccontainsabout1millionrhodopsinmolecules.Suchastructureisobviouslybeneficialtomakethelightquantumenteringtheretinahaveagreaterchanceofencounteringrhodopsinmoleculesintheoutersegment.

Someoneusedintracellularmicroelectrodetechnologytostudythechangesinthepotentialdifferencebetweentheinnerandoutersegmentsoftherodcellsbeforeandafterlight.Theresultsfoundthatwhentheretinaisnotirradiated,therestingpotentialoftherodcellsishigherthannormal.Thecellsaremuchsmaller.TheanalysisshowsthatthisiscausedbyaconsiderablenumberofNachannelsintheopenstateandcontinuousNainflowintheoutermembranewhenthereisnolight,whilethecontinuousmovementoftheNapumpintheinnermembranemovesNaoutofthemembrane.,SoastomaintaintheNabalanceinsideandoutsidethemembrane.Whentheretinaisexposedtolight,thepotentialonbothsidesoftheoutersegmentmembranecanbeseentochangetemporarilytothedirectionofhyperpolarization.Itcanbeseenthattheoutersegmentmembraneisinconsistentwiththegeneralcellmembrane.Itisdepolarizedinthedarkorwithoutlight.Thetransmembraneelectrolysischangestohyperpolarizationwhenitisstimulatedbylight.Therefore,thereceptorpotentialoftherodcells(thesameistruefortheconecells)appearsasahyperpolarizedslowpotential.Itisspecialamongallthegeneratorsorsensorpotentialsthathavebeenstudied.Theyaregenerallyexpressedasatemporarydepolarizationofthe membrane .

Themechanismbywhichtheabsorptionofphotonscauseshyperpolarizedelectricalreactionsintheoutersegmentmembranehasbeenbasicallyunderstood.Thisistheabsorptionofphotonsbyrhodopsinasthereceptor,whichcausesthedeconstructionofopsinmoleculesandstimulatesthem.Seacucumbershaveanintermediarycalledtransducin(transducin)Ctintheopticdiscmembrane.ThelatterisamemberoftheG-proteinfamilystructurally.Theresultofitsactivationistoactivatenearbyphosphodiesterase,thuscausingexternalThecGMPinthecytoplasmofthesegmentisdecomposedinalargeamount,andthedecompositionofcGMPinthecytoplasmmakesthecGMPboundtotheoutersegmentmembranewhenitisnotstimulatedbylighttobedecomposedbythedissociationofthemembrane,andtheexistenceofcGMPonthemembraneispreciselythis.TheconditionsfortheopeningofchemicallygatedNachannelsinthemembranereducethecGMPonthemembraneandtheopeningofNachannels.Asaresultofthelight,thehyperpolarizedsensorpotentialwehaverecordedappears.Itisestimatedthatwhenarhodopsinisactivated,about500transferinscanbeactivated;althoughtransferinsactivatephosphodiesteraseonetoone,anactivatedphosphodiesterasetakesapproximatelyonesecondItcandegrademorethan4,000cGMPmolecules.Duetothebiologicalamplificationeffectoftheenzymesystem,itcanbeexplainedwhytheeffectofalightquantumcancausetheclosureofalargenumberofchemicallygatedNachannelsontheoutermembrane,causingahyperpolarizedelectricitythatissufficientforthehumanvisualsystemtoperceive.Variety.

Theoutersegmentoftherodcellandtheentirerodcellhavenoabilitytogenerateactionpotentials.Thesensorpotentialcausedbythelightstimulationontheoutersegmentmembranecanonlyreachitsfinalfootwithanelectrotonicspread.Partofitaffectsthereleaseoftransmittersoutsidetheendpoint(equivalenttotheaxonend).

Transducedvision

Theoutersegmentoftheconesystemalsohasadisc-likestructuresimilartorodcells,andcontainsspecialphotosensitivepigments,but molecules Thenumberissmall.Itisknownthatmostvertebrateshavethreedifferentconepigments,eachofwhichexistsinadifferentconecell.Thethreeconepigmentsallcontainthesame11-cis-retinal,butthemolecularstructureoftheopsinisslightlydifferent.Itseemsthattheslightdifferenceinthemolecularstructureofopsindetermineswhichwavelengthoflighttheretinalmoleculecombinedwithitismostsensitiveto.Therefore,therearerhodopsininrodcellsandthreedifferenttypesofoptics.Thedifferencebetweenconepigments.Whenlightactsontheoutersegmentoftheconecells,thesuper-receptorpotentialsimilartothatoftherodcellsalsooccursonbothsidesoftheiroutersegmentmembrane,asthefirststepofphoto-electricconversion.Itisbelievedthatthetransductionmechanismoftheoutersegmentofconecellsissimilartothatofrodcells.

Animportantfeatureofconecellfunctionisitsabilitytodistinguishcolors.Colorvisionisacomplexphysical-psychologicalphenomenon.Thedifferenceincolorismainlythesubjectiveimpressionofthehumanbraincausedbylightofdifferentwavelengthsactingontheretina.Thehumaneyecangenerallydistinguishsevencolorsofred,orange,yellow,green,cyan,blue,andpurpleonthespectrum,andeachcolorcorrespondstoacertainwavelengthoflight;butacarefulinspectioncanrevealthatthehumaneyealoneThereareactuallynolessthan150differentcolorsinthespectrum,whichmeansthataslongasthewavelengthlengthincreasesordecreaseswithintherangeofthevisiblespectrum,itcanbedistinguishedintodifferentcolorsbythevisualsystem.Obviously,itisimpossibletoimaginethattherearehundredsofconecellsorphotosensitivepigmentsintheretinathatrespondtolightofdifferentwavelengths.ButphysicshasknownfromNewton'stimeorearlierthatacolormaynotonlybecausedbyacertainfixedwavelengthoflight,butalsobythemixingoftwoormoreotherwavelengthsoflight.Forexample,rotatingthesevencolorsoflightonthespectrumontheso-calledNewtoniancolorwheelcancauseawhitesensationinthehumaneye;usingred,green,andbluelight(notthepigmentsofthesethreecolors)forpropermixingcancausethespectrumAllthefeelingofanycolor.Thislatterphenomenonisparticularlyimportant;thisso-calledthree-primarycolormixingprinciplehasnotonlybeenwidelyusedincolorphotography,colortelevision,etc.,butalsousedtoexplaintheprincipleofcolorvision.Asearlyasthebeginningofthelastcentury,Young(1809)andHelmholtz(1824)proposedthetheoryofthreeprimarycolorsofvision.Itwasassumedthattherearethreekindsofconecellsorcorrespondingthreekindsofconecellsthatareparticularlysensitivetored,red,andbluelightintheretina.Akindofphotosensitivepigment,anditisassumedthatwhenthelightonthespectrumandthelightbetweenthesethreeactsontheretina,theselightscanstimulatethetwoconecellsorphotosensitivepigmentswithsimilarsensitivewavelengthstodifferentdegrees,soInthecenter,itcausesthesensationofothercolorsbetweenthetwoprimarycolors.Thetheoryofvisualthreeprimarycolorsusestheassumptionofsimplerbiologicalperceptionstructuretoexplainthecomplexcolorvisionphenomenon,whichisgenerallyacceptedbymostpeople.However,attemptstofindthesamekindofconecellsorphotosensitivepigmentsintheexperimenthavebeenunsuccessfulforalongtime.Theopticalmicroscopeandtheelectronmicroscopecannotfindanydifferenceinthestructureoftheconecells.Atthesametime,itisnotpossibletoseparatethedifferentconephotosensitivepigmentsbygeneralchemicalmethods.

Duetotheadvancementofexperimentaltechnology,thehypothesisthattherearethreeconecellsintheretinathatareparticularlysensitivetolightofdifferentwavelengthshasbeenconfirmedbymanyexcellentexperiments.Forexample,somepeopleusenomorethanasingleconediameterThesmallmonochromaticlightbeamswereexaminedonebyoneanddrawninthebody(theinitialexperimentwascarriedoutinanimalssuchasgoldenmalesandsalamanders,andlaterinhumans).Itwasfoundthatallthedrawncurveswerenomorethanthreetypes.Theyrepresentthreetypesofconecellswithdifferentspectralabsorptioncharacteristics.Onetypehasanabsorptionpeakoutsideof420nm,onetypeisoutside531nm,andtheothertypeisoutside558nm,whichisalmostexactlyequivalenttothewavelengthsofblue,green,andredlight,andTheabovehypothesisofthethree-primary-colortheoryofvisionisconsistent.Themethodofrecordingthereceptorpotentialofasingleconecellwithamicroelectrodehasalsoobtainedsimilarresults,thatis,themagnitudeofthehyperpolarizedreceptorpotentialcausedbydifferentsinglebeamsisdifferentindifferentcones,andthepeakappearanceisconsistentYuthetheoryofthreeprimarycolors.

Thetheoryofthreeprimarycolorsanditsexperimentalbasiscangenerallyexplainthepossiblepathogenesisoftheso-calledcolorblindnessandcolorweaknessencounteredinclinicalpractice.Protanopiaisalsocalledfirstcolorblindness,whichisbelievedtobecausedbythelackofconecellsthataresensitivetolongerwavelengthsoflight;therearealsogreenblindness,alsocalledsecondcolorblindness,andblueblindness,alsocalledthirdprimarycolorblindness,whichmaybecausedbyDuetolackofcorrespondingspecialconecells.Protanopiaanddeuteranopiaaremorecommon,andtheyarenotdistinguishedclinicallyasred-greenblindness;blueblindnessisveryrare.Thecolorofacolorblindpatientcannotonlydistinguishgreen,butalsocannotdistinguishbetweenredandgreen,greenandblue,etc.Somepeoplewithabnormalcolorvisionareonlylessabletorecognizeacertaincolor,thatis,theyarenotduetolackofacertainkindofconecells,buttheresultofthelatter'sweakerresponseabilitythannormalpeople.Thissituationisdifferentfromtherealone.Colorblindnessiscalledcolorweakness.Exceptforaverysmallnumberofcolorblindnesscanbecausedbyacquireddiseasesoftheretina,thevastmajorityaredeterminedbygeneticfactors.

Althoughthetheoryofthreeprimarycolorssatisfactorilyexplainsmanycolorvisionphenomenaandthecausesof colorblindness ,andhasbeenexperimentallyconfirmedatthelevelofphotoreceptivecells,itcannotexplainallofthem.Colorvisionphenomena,suchascolorcontrast,areanexample.Tryputtingasmallbluepieceofpaperonayelloworothercoloredbackground.Youwillfeelthatthebluepieceofpaperplacedonayellowbackgroundisparticularlyblue.Atthesametime,youfeelthatthebackgroundismoreyellowthanwhenthebluepieceofpaperisnotplaced(innorthernChina).OntheLoessPlateau,whenthewindinthespringcausesyellowdusttoobscurethesun,itwillfeelthatthe light oftheordinarysun-shakinglampbecomesbluer).Thisphenomenoniscalledcolorcontrast,andyellowandbluearecalledcontrastingcolorsorcomplementarycolors.Thecolorcontrastphenomenononlyappearsbetweencontrastingcolors,notbetweenanytwocolors.Therearestillcontrastingcolorpairs:redandgreen,andblackandwhite.Accordingtocolorcontrast,itisnoteasytousethetheoryofthreeprimarycolorstocompletevisualphenomena.Almostatthesametimewhenthetheoryofthreeprimarycolorswasproposed,anothertheoryofcolorvisionappeared,calledthetheoryofcontrastingcolors.Thistheoryproposesthattherearethreesubstancesintheretina,eachofwhichreactsoppositelytoasetofcontrastingcolorstimuli.Asmentionedearlier,theresearchconductedattheconelevelinrecentyearsisconducivetothetheoryofthreeprimarycolorsbutnottothetheoryofcontrast.However,someexperimentsperformedoncellsinotherlayersoftheretinaconformtothespeculationofthetheoryofcontrast.Forexample,microelectrodestudiesconductedongoldfishlevelcellsshowthatthesecells,unlikerodsandcones,canhavehyperpolarizedtransmembrane potential changesaswellasdepolarization.Whenstimulatedwithavarietyofdifferentcolorsoflight,itwasfoundthatsomehorizontalcellsshowedthelargestdepolarizationresponsewhenstimulatedbyyellowlight,andthelargesthyperpolarizationresponsewhenstimulatedbybluelight;Therearesimilardifferentresponsestoredandgreenstimuli.Thesephenomenaareconsistentwiththetheoryofcontrastingcolors.Itseemspossiblethatthetwocolorvisiontheories,whicharebasedonpartialcolorvisionphenomena,arebothpartiallycorrect.Attheconelevel,differentcolorsoflightcancausethreedifferentconecellstoproducehyperpolarizedelectricityofdifferentsizes.Changesarecoded;butatthelevelofhorizontalcellsorotherlevelsofcells(includingsomecentralneurons),theinformationisre-encoded.Differentcolorpairscanbecodedbytheoppositeformofelectricalresponseofthesamecelltothecontrastingcolorsofeachother..Theabovefactsshowthatthecauseofcolorvisionisaverycomplicatedprocess,whichrequirestheparticipationofmulti-levelneuralcomponentsfromretinalconestocorticalneurons.

Informationprocessing

Theelectricalsignalsgeneratedbyrodsandconesneedtobetransmittedthroughacomplexcellnetworkintheretina,andfinallynervefiberscanbegeneratedbyganglioncellsItistransmittedtothecenterintheformofactionpotentials.Becausethearrangementandconnectionofvariouscellsintheretinaareverycomplicated,therearemanykindsofchemicalsubstancesrelatedtothetransmissionofinformationbetweencells(exceptforthecommontransmittersinthegeneralnervoussystem,togetherwiththevariousneuropeptidesfoundintheretina,Thetotalnumberhasreachedmorethan30kinds),sovisualinformationmustundergovariouschangeswhenitistransmittedfromphotoreceptorcellstoganglioncells;thisisactuallytheinitialprocessingofvisualinformationbytheretinaitself,whichisconstructedinspecificcellsandchemicalstructuresoftheretina.Accordingtocertainrulesinthenetwork,buttheunderstandingoftheserulesisstillverysuperficial.Whatcanbepreliminarilyconfirmedisthatbipolarcells,horizontalcellsandmostamacrinecells,likethetwophotoreceptorcells,havenoabilitytogenerateactionpotentials(butsomeamacrinecellscangenerateactionpotentials);thesethreeThedifferencebetweenthesecellsandphotoreceptorcellsisthatundertheinfluenceofthepreviouscells,theycanproducebothsuper-modifiedslowpotentialsanddepolarizedslowpotentials(equivalenttothepostsynapticmembraneofgeneralneurons).IPSpandEPS).Alltheseslowpotentialscanonlybeusedfortheexpansionofelectrotonicity,affectingthechangesinthereleaseofpresynapticmembranetransmitters,causingslowpotentialchangesinthenextlevelofcells(includingelectricalsynapticinteractions);onlywhenWhensuchaslowpotentialistransmittedtotheganglioncellbody,becausethelatterhastheabilitytogenerateactionpotentials,whenthesumofthetwotypesofslowpotentialsmakestherestingmembranepotentialoftheganglioncelldepolartothethresholdpotentiallevel,Onlythenwillan"all-or-nothing"actionpotentialbegenerated,whichistransmittedtothecenterasthefinaloutputsignaloftheretina.Onlyganglioncellscangenerateactionpotentials.Althoughthedetailsoftheinformationprocessingintheretinaarenotveryclear,itisbettertotreattheretinaasa"blackbox"incybernetics.Onlyitsinput(equivalenttothelightactingontheretina)Stimulus)anditsinput(equivalenttotheactionpotentialsequencesentbytheopticnerve)arecomparedandanalyzed,sothatthefinalresultofretinalinformationprocessingandcodingcanalsobeinitiallyunderstood.Thefirstthingtorememberisthefactthatthetotalnumberoffibersintheopticnerve(thatis,thetotalnumberofganglioncells)isonly1%ofallphotoreceptorcells.Thissimplefactsufficestoexplainthattheopticnervecannottransmitthelightofthephotoreceptorcellsintheretinathroughitsfibers"point-to-point"(exceptforafewconecellsinthefovea);therefore,mostofthesignalstransmittedbytheopticnervefibersareonlyItcanbedeterminedbymultiplephotoreceptorcellsandthereforecontainsmoreinformation.

Themethodofstimulatingthecat'sretinawithasmalllightspotandrecordingtheactionpotentialofasingleopticnervefiberatthesametimeshowsthattheganglioncellsthatemitopticnervefiberscanberoughlydividedintothreetypes,namelyX-,Y-andW-cell.ThecharacteristicofX-andY-cellsisthattheybothhavea"center-peripheralreceptivefield"thatisroughlyconcentric;thereceptivefieldofaganglioncellherereferstoaspecificareaontheretina,whichmaybestimulatedwhenthelatterisstimulated.Maketheganglioncellreact;thereceptivefieldofthesetwokindsofcellsiscomposedoftwoparts;whenthelightactsonthecentralpartofthereceptivefield,theganglioncelldischargeincreases,andwhenthelightactsontheretinainacertainrangearoundthecenterInsomecases,thedischargeoftheganglioncellisreduced.Thisisatypeofcenter-peripheralreceptivefield.Thisiswhenthecentralpartofthereceptivefieldreceiveslightstimulation,thenumberofdischargesoftheganglioncelldecreases,andwhentheperipheralpartisstimulated,itisonthecontraryCausedbytheincreaseofthecelldischarge,thiskindofganglioncellcanbecalledthecentrallight-withdrawingresponsecell.

BothX-andY-cellscanhavetheabovetwotypesofreceptivefields.ThedifferencebetweenthemisthatthereceptivefieldofX-cellsissmall,andtheresponsetostimuliiscontinuous;thereceptivefieldofY-cellsislarger,andtheresponseistemporalandhasanon-linearrelationshipwiththestimulus.Inmonkeyexperiments,itwasalsofoundthatdifferentX-cellsresponddifferentlytodifferentwavelengthsoflight,butarenotsensitivetochangesintheintensityoflight;whileY-cellsaresensitivetochangesintheintensityoflight,butarenotsensitivetochangesinthewavelengthoflight..AsforW-cells,theyhaveamuchlargerreceptivefieldthantheformertwo.Theyeitherdischargewhenlightisstimulatedorwhenlightiswithdrawn,buttheyrespondslowlytothestimulusandgenerallydonothavetheoppositeperipheralproperties.Fieldofview.Fromthemorphologicalpointofview,X-andY-cellsmainlyreceiveinputfrombipolarcells,whileWcellsmainlyreceiveamacrinecells.

Thenerveimpulseoneachopticnervefiberdoesnotsimplymeanthatacertainpartoftheretinaisexposedtolightornolight.TakingtheaboveX-asanexample,itsstrongestdischargeoccursinthecentralpartofitsreceptivefield.Whenthereisnolightontheouterperiphery(orviceversa);ifthecenterandouterperipheryareexposedtolightatthesametime,thedischargeofthecellsinthissectionwillnotchangeorincreaseonlyslightly.Inaddition,therearefactsthattheretinalimagehasbeendecomposedintodifferent"pixels"afterbeingprocessedbytheretina.Forexample,theresidencesofthewavelengthsoftheimagetransmittedbythenodularcellcentertransmititsdifferentbrightness.Thiskindofdecompositionofperceptioninformationintoitsconstituent“elements”,andthen“parallel”transmissionandprocessingintheperceptionpathway,isoftenencounteredintheresearchofvarioussensoryfunctionsofthebrain,buthumanvisionisalsodifferentfromothersensations.Similarly,themostcomplexinformationprocessingandprocessingtakesplaceinthecenter,especiallyitshigh-levelparts.

Otherphenomena

Darkadaptationandlightadaptation

Whenapersonentersadarkroomfromabrightplace,hecannotseeanythingatfirst.Afteracertainperiodoftime,hisvisualsensitivityItgraduallyincreasesthemainbodyandrestoresthevisioninthedark.Thisiscalleddarkadaptation.Onthecontrary,whenyoucomefromthedarkplacetothebrightplace,youfeeladazzlinglightatfirst,youcan'tseetheobjectclearly,andyoucanonlyrestoreyourvisionafterawhile.Thisiscalledbrightadaptation.

Darkadaptationisaprocessinwhichthehumaneye'ssensitivitytolightgraduallyincreasesinthedark.Atdifferenttimesafterenteringthedarkroom,continuouslymeasurethehumanvisualthreshold,thatis,measuretheintensityofthelightstimulusthatthehumaneyecanjustperceive.Itcanbeseenthatthisthresholdgraduallydecreases,thatis,theprocessofvisualsensitivitygraduallyincreasinginthedark.Generally,withinthefirst7minutesafterenteringthedarkroom,thereisaperiodofsignificantdeclineinthethresholdvalue,andthentheamountofthethresholdvaluesignificantlydecreases;about25-30minutesafterenteringthedarkroom,thethresholdvaluedropstothelowestpointandstabilizesInthisstate.Themechanismofdarkadaptationisrelatedtotheincreaseinthere-synthesisofphotosensitivepigmentsintheretinainthedark,thusincreasingtheamountofpigmentsintheundecomposedstateintheretina.Accordingtoanalysis,thefirststageofdarkadaptationismainlyconsistentwiththeincreaseinthesynthesisofconecytochromes;thesecondstage,themaincomponentofdarkadaptation,isrelatedtotheenhancedsynthesisofrhodopsininrodcells.

Mingadaptsquicklyandtakesaboutoneminutetocomplete.Thedazzlinglightperceptionismainlyduetothefactthatthesyntheticrhodopsinaccumulatedinthedarkisquicklydecomposedwhenitentersthebrightplace,becauseitssensitivitytolightishigherthanthatofthephotosensitivepigmentintheconecells;Aftertherodcytochromeisrapidlydecomposed,theconecytochrome,whichislesssensitivetolight,canbephotosensitiveinthebrightlightenvironment.

Fieldofview

Singleeyefixedlystaresatthefrontwithoutmoving,andtherangethattheeyecanseeatthistimeiscalledthefieldofview.Themaximumlimitofthevisualfieldshouldbeexpressedbythesizeoftheanglebetweenitandthevisualaxis(whenasingleeyeislookingatacertainpointintheoutsideworld,theimageofthispointisexactlyinthefoveaof​​theretina,andtheimaginarylineconnectingthesetwopointsisthevisualaxis).Underthesamelightingconditions,thesizeofthefieldofviewmeasuredwithdifferentcolortargetsisdifferent,thewhitefieldofviewisthelargest,followedbyyellow-blue,redagain,andthegreenfieldofviewisthesmallest.Itisassumedthatthesizeofthefieldofviewisnotonlyrelatedtothedistributionrangeofvariousphotoreceptorcellsintheretina,butalsolacksasatisfactoryexplanationindetails.Inaddition,becausethefacialstructureblocksthelineofsight,italsoaffectstheshapeofthevisualfield.Forexample,thevisualfieldonthetemporalsideoftheaveragepersonislarger,andthevisualfieldonthenasalsideissmaller.Theclinicianchecksthefieldofvision,usingaspecialperiscope,andusingdifferentcoloredoptotypestocheck,thepurposeistounderstandthegeneralphotosensitiveabilityoftheretina,andsometimescanbeusedtofindalargerrangeofretinopathy.Certaindiseasesoftheretina,opticnerve,orvisualconductionpathwayhavespecialformsofvisualfielddefects,whicharemeaningfulindiagnosis.

Electroretinogram

Aguideelectrodeisplacedincontactwiththecornea,andtheotherelectrodeisplacedontheforeheadasareferenceelectrode.Whentheretinaisextensivelystimulatedwithlight,itcanbeAseriesofelectricalchangesarerecordedonthemeasuringinstrument,whichiscalledanelectroretinogram.Theelectroretinogramisdifferentinnaturefromtheelectricalphenomenarecordedbythesamemicroelectrodeinasingleretinalcellcomponent;theelectroretinogramisacomprehensivereflectionofmultipleelectricalresponsesofvariouscomponentsintheentireretinawhenexposedtoawiderangeoflight.Itusuallyconsistsofthreewavesnameda,b,andc.Accordingtoexperimentalanalysis,theawaveismainlyderivedfromthesensorpotentialofphotoreceptorcells;thebwavehasalargeramplitude,whichismainlyrelatedtotheactivityofcellssuchasbipolarcells;thecwaveisgentleandhasalongduration,whichmayberelatedtotheactivityofthepigmentcelllayer.Sometimeswhenthelightisremoved,therewillbeanotherwaveontheslowandcontinuouscwave,calledthedwave,thecauseofwhichisstillunclear.Althoughelectroretinogramiseasytomeasureandtrace,itreflectsthespecificityofretinalfunctionalstatusorpathologicalchanges.Atpresent,onlyafewdiseaseshavespecialelectroretinogramchanges,soitisoflittleclinicalsignificance.

Binocularvisionandstereovision

Theeyesofhumansandhighermammalsareallinfrontoftheface,andtheimagesofsimilarpartsofthevisualfieldofthetwoeyeswhenlookingatobjectsaretransmittedthroughtheirownuniqueneuralpathways.Tothecenter,butnormalpeopleonlyproduceasenseof"thing"inthesubjectiveobservationsense.Theprerequisiteforthetwoeyestoseeobjectsandproduceonlyonevisualimageisthatthelightfromthesamepartofthesubstanceshouldbeimagedonthecommensuratepointsoftheretinaonbothsides.Forexample,themaculasofthetwoeyesarecommensuratepoints;whenthetwoeyeslookatasmallblackspotontheculturewall,duetotheadjustmentoftheextraocularmuscles,thisspotisexactlyimagedonthemaculasofbotheyes.Onlyonepointis"seen"invision;atthistime,ifyougentlypushtheoutsideoftheeyeballwithyourhandtoshiftthevisualaxisoftheeyeslightly,thentheblackdotimageontheretinaoftheeyewillmoveawayfromthemacula.,Fallingonapointthatisnotcommensuratewiththeimageoftheoppositesideoftheretina,soyouwillfeelthattherearetwoblackspotsonthewall,thisisthephenomenonofdoublevision.Obviously,outsidethemacula,thetemporalretinaofoneeyeandthenasalretinaoftheothereyearesymmetricalwitheachother;andthenasalretinaofoneeyeisalsosymmetricalwiththetemporalretinaoftheotherjustright.