3.22-3.24 Visual System Central Visual Processing

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1、3.22-3.24VisualSystem:CentralVisualProcessing1.ThedistributionoftheaxonsofretinalganglioncelltomajorprocessingcentersVisualprocessingbeginsinthetworetinae.Theaxonsoftheretinalganglioncells,theprojectionneuronsoftheretina,formtheopticnervethatextendstoamidlinecrossingpoint,theopticchiasm.B

2、eyondthechiasmfibersfromthetemporalhemiretinasproceedtotheipsilateralhemisphere;fibersfromthenasalhemiretinascrosstothecontralateralhemisphere(Figure25–5).Becausethetemporalhemiretinaofoneeyeseesthesamehalfofthevisualfield(hemifield)asthenasalhemiretinaoftheother,thepartialdecussationoffi

3、bersatthechiasmensuresthatalltheinformationabouteachhemifieldisprocessedinthevisualcortexofthecontralateralhemisphere.Beyondtheopticchiasmtheaxonsfromnasalandtemporalhemiretinascarryinginputfromonehemi-fieldjoinintheoptictract,whichextendstothelateralgeniculatenucleusofthethalamus.Thelate

4、ralgeniculatenucleusinprimatesconsistsofsixlayers,eachofwhichreceivesinputfromeithertheipsilateralorthecontralateraleye.Becauseeachlayercontainsamapofthecontralateralhemifield,sixconcordantmapsarestackedatoponeanother.Thethalamicneuronsthenrelayretinalinformationtotheprimaryvisualcortex.P

5、athways:Theprimaryvisualpathwayisalsocalledthegeniculostriatepathwaybecauseitpassesthroughthelateralgeniculatenucleusonitswaytotheprimaryvisualcortex,alsoknownasthestriatecortexbecauseofthemyelin-richstripethatrunsthroughitsmiddlelayers.Eachlateralgeniculatenucleusprojectstotheprimaryvisu

6、alcortexthroughapathwayknownastheopticradiation.Theseafferentfibersformacompleteneuralmapofthecontralateralvisualfieldintheprimaryvisualcortex.Asecondpathwayfromtheretinarunstothesuperiorcolliculusandisimportantincontrollingeyemovements.Thispathwaycontinuestothepontineformationinthebrains

7、temandthentotheextraocularmotornuclei.Athirdpathwayextendsfromtheretinatothepretectalareaofthemidbrain,whereneuronsmediatethepupillaryre-exesthatcontroltheamountoflightenteringtheeyes.2.FunctionalorganizationofV1A.theprimaryvisualcortex(V1)isalsoknownasthe“striateco