Courte introduction
Concept
Vision centrale isthenervecellinthecerebralcortexthatisinvolvedintheformationofvisiongroup.Itislocatedontheoccipitalcortexonbothsidesofthetalarfissure, thatis, theuppercuneiformgyrusandthelowerlingualgyrus.Becauseofthespecialstructureofthecortex, therearewhitefinelinesonthecrosssection, soitisalsocalledthestriatedarea.Thevisualcenterofeachhemisphereisrelatedtohalfofthevisualfieldofbotheyes, sototalblindnessoccurswhenthevisualcentersofbothhemispheresarecompletelydamaged.
Emplacement du cerveau
Thevisualareaof thehumancerebralcortexislocatedintheoccipitallobe (area17) .Theleftoccipitalcortexreceivesafferentnerveprojectionsfromthetemporalretinaofthelefteyeandthenasalretinaoftherighteye.Therightoccipitalcortexreceivesafferentfiberprojectionsfromthetemporalretinaoftherighteyeandthenasalretinaofthelefteye.Theupperhalfoftheretina (thelowerquadrantofthefieldofview) isprojectedtotheupperedgeofthetalariacleft; thelowerhalf (theupperquadrantofthefieldofview) isprojectedtotheloweredgeofthetalariscleft.Therefore, damagetotheloweredgeofthetalusfissurewillappearasadefectintheupperquadrantintermsofhumanvision.Themacularareainthecenteroftheretinaisprojectedtothebackofthetaluscleft, andthemarginalareaisprojectedtothefrontofthetaluscleft.Therepresentativeareaof themaculaisrelativelylargerinboththecortexandthelateralgeniculatebodythantheborderrepresentativearea.
Le mécanisme central de formation de la vision
Le processus de formation de la vision
Cellsareexcited, andthecellsattheleveloftheretinaarecomposedandanalyzedinaloop.Thex, Y, andWneuronsparticipateinthecontrast, orientation, distanceandothermechanismsofthesurfaceoftheextractedobject.Differentneuronshavedifferentorientations, differentspatialfrequencies, andimages.TheresponseofthevisualsystemisbasedontheperformanceoftheFourieralgorithm, andthenthevisualsystemextractsprimitiveprimitivesfromtheretinalscenetoperformsymbolgroupoperations.Inthisway, visualinformationpassesthroughvisualcells, bipolarcells, horizontalcells, andganglioncells, andpassesthroughtheopticnerve.The forme « en série » informationpatternistransmittedtothelateralgeniculatebodytobedecodedintoa « treillis », andthentransmittedbyopticradiationtodifferentfunctionalareasoftheprimaryvisualcortex, andfinallytransmittedtothecorrespondingdivisionoflaborareasofthehigh- zone de niveau, et intégrée dans différentes zones corticales pour produire une connaissance complète de l'information visuelle.
La voie centrale de vision et de positionnement cortical
Thevisualpathwayconsistsoffourlevelsofneurons, Thefirst, deuxième, andthirdlevelsofneuronsarelocatedintheretina, andthefourthlevelofneuronsislocatedontheoutsideThegeniculatebody, fromwhichthenervefibersarefinallyterminatedintheopticcenterofthecerebralcortex.Theopticnerve, whichiscomposedofaxonsofthird-levelneurons (ganglioncells), entersthecranialcavityafterleavingtheeyeball.Itmergesintotheopticchiasmatthebottomofthethirdventricle, wherehalfofthefiberscrosstotheoppositeside.Theruleisthatthefibersfromthenasalretinaofbotheyes (thatis, thepartthatreceiveslightstimulationfromthetemporalside) crosstothecontralateralsideandascendtothecontralaterallateralgeniculatebody.Thefibersfromthetemporalretina (thatis, thepartthatreceiveslightstimulationfromthenasalside) donotcross, andascendtotheipsilaterallateralgeniculatebody.Inthisway, theleftandrighthalvesoftheentirefieldofviewareprojectedtotheoppositecerebralhemispheres.Theopticnervefibersformtheleftandrightoptictractsafterpassingthroughtheopticchiasm , et certains d'entre eux eachthesuperiorcolliculusofthequadruplex, andparticipateinactivitiessuchasvisualaccommodationreflex, lightreflex, andvisualmotorreflex; mostofthefibersstopatthelateralgeniculatebody.Theinternalstructureofthelateralgeniculatebodyiscomposedof6layersofnervecells, andthepartsrelatedtocentralvisionandperipheralvisioncanbeclearlydistinguished.Theopticnervefibersfromtheintersectioncorrespondingtothefoveaterminateinlayers1,4, et6, andthenon-intersectingopticnervefibersterminateinlayers2,3, and5.Thoseequivalenttothenear-peripheralareastopat1,6,2, and3layersrespectively, andthoseinthefar-peripheralareastopatlayers1,2respectively.Theendofeachopticnervefiberisdividedinto5-6smallbranches, eachofwhichterminatesinacellbodyofthelateralgeniculatebody, plutôt que lesendrites.Par conséquent,chaquefoisunefibrenerveuxoptiqueestendommagé,ilestpossiblededégénérerlescellulesdanslescouches2,3,et5surlecôtéipsilatérauxoulescouches1,4,et6surlecôtécontralatéral. daunestationrelaisentrelecortexcérébraletlarétine.