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Physiology of retina
- 1. PHYSIOLOGY OF RETINA DR.SHIVRAJ
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- 7. OUTER PLEXIFORM LAYER SNAPSESBETWEEN ROD SPHERULES CONE PEDICLES WITH DENDRITES OF BIPOLAR CELLS AND PROCESSES OF HORIZONTAL CELLS
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- 14. INITIATION OF VISION- PHOTOTRANSDUCTION PROCESSINGAND TRANSMISSION OF VISUAL SENSATION VISUAL PERCEPTION
- 15. LIGHT FALLING UPONTHE RETINA CAUSES PHOTOCHEMICAL CHANGES RHODOPSIN BLEACHING RHODOPSIN REGENERTION VISUAL CYCLE GENERATION OF RECEPTOR POTENTIAL PHOTOTRANSDUCTION
- 16. STIMULI FOR VISUALSENSATION INADEQUATE STIMULI • PRODUCE GLOWING SENSATION CALLED PHOSPEHENES • EX. MECHANICAL STIMULUS BY PRESSURE ON SCLERA – PRESSURE PHOSPHENE,ELECTRIC CURRENTS- ELECTRICAL PHOSPHENES,ETC ADEQUATE STIMULI • FORMED BY VISIBLE PORTION OF ELECTROMAGNETIC RAADIATION (400nm- 750nm)
- 17. VISUAL PIGMENTS • SUBSTANCESHAVING THE PROPERTY TO ABSORB LIGHT • PEAK OF EACH PIGMENTS ABSORPTION CURVE IS CALLED ITS ABSORPTION MAXIMUM • MADE OF PROTEIN OPSIN AND RETINENE(RETINAL) , THE ALDEHYDE OF VITAMIN A RHODOPSIN (VISUAL PURPLE) CONE PIGMENTS SCOTOPIC VISION TRICHROMATIC PIGMENTS ABSORPTION SPECTRUM 493nm-505nm PEAK ABSORPTON WAVELENGTH BLUE-435NM (CYANOLABE) GREEN-535NM (CHLOROLABE) RED-580NM (ERYTHROLABE) PRESENTS IN DISC OF OUTER ROD SEGMENTS BLUE SENSITIVE CONES- LEAST PREVALENT
- 18. VISUAL CYCLE EQILIBRIUM BETWEENPHOTODECOMPOSITION AND REGENRATION OF VISUAL PIGMENTS RHODOPSIN BLEACHING RHODOPSIN REGENERATION PHOTODECOMPOSITION
- 19. METARHODOPSIN II ACTIVATES PHOSPHODIESTERASES CONVERSIONOF c GMP TO GMP REDUCTION IN c GMP IN PHOTORECEPTOR PRODUCTION OF ELECTRICAL RESPONSE(RECEPTOR POTENTIAL) BLEACHING OF THE RETINAL PIGMENTS OCCURS UNDER THE INFLUENCE OF LIGHT WHEREAS REGENERATION OCCURS INDEPENDENT OF LIGHT TOTAL ROD BLEACHING OCCURS BEFORE SIGNIFICANT BLEACHING CAN BE OBSERVED IN CONES SETTING ASIDE SCOTOPIC ROD FUNCTION FROM THE PHOTOPIC PORTION WHICH FUNCTIONS DURING BRIGHT LIGHT
- 20. PHOTOTRANSDUCTION STANDING POTENTIAL • INNERSEGMENT OF PHOTORECEPTOR CONTINOUSLY PUMPS Na+ FROM INSIDE TO OUTSIDE REATING NEGTIVE POTENTIAL INSIDE CELL • Na+ CHANNELS IN OUTER SEGMENT ARE KEPT OPEN BY c GMP CAUSING Na+ FROM ECF TO FLOW INTO IT IN DARK • OUTER SEGMENT IS HYPOPOLARISED COMPARED TO INNER SEGMENT THAT IS CURRENT FROM INNER SEGMENT TO OUTER SEGMENT • IN DARK THERE IS INFLUX OF Ca+ INTO THE CELL BY c GMP GATED CHANNELS HYPERPOLARISING RECEPTOR POTENTIAL • DECREASE IN c GMP IN PRESENCE OF LIGHT CLOSES SOME OF THE Na+ CHANNELS CAUSING HYPERPOLARISING RECEPTOR POTENTIAL • IN DARK ELECTRONEGATIVITY IN PHOTORECEPTORS IS 40mV AND AFTER EXCITATION REACHES 70mV • IT IS A GRADED POTENTIL • CONE RESPONSES ARE PROPORTIONAL TO STIMULUS INTENSITY AT HIGH LEVEL OF ILLUMINATION WHEN ROD RESPONSES ARE MAXIMAL AND CANNOT CHANGE CAUSING CONES TO PRODUCE GOOD RESPONSES TO CHANGE IN LIGHT INTENSITY
- 21. IN PRESENCE OFLIGHT DECREASE Na+ CONCENTRATION CAUSING HYPERPOLARISAION OF CELLS Ca+ CONCENTRATION DECREASES CAUSING DECREASE IN RELEASE OF NEUROTRANSMITTER DEPOLARISATION OF ON CENTRE BIPOLAR CELLS (RODS AND CONES ) AND HYPERPOLARISATION OF OFF CENTRE CONE BIPOLAR CELLS ACTIVATION OF RETINAL GANGLION CELLS SIGNAL TO BRAIN SOME BIPOLAR CELLS RECEIVE SIGNAL INDIRECTLY THROUGH HORIZONTAL CELLS WHICH BEIG INHIBITORY CELLS INVERSES THE POLARITY OF RESPONSE
- 23. RECEPTIVE FIELDS OFBIPOLAR CELLS
- 24. LATERAL INHIBITION • LIGHTFALLING ON RETINA EXCITES ONLY CENTRAL MOST AREA WHERAS THE AREAAROUND IS INHIBITED • HORIZONTAL CELLS TRANSMIT SIGNALS HORIZONTALY INBOUTER PLEXIFORM LYER FROM RODS AND CONES TO BIPOLAR CELLS • RECIPROCAL RELATIONSHIP BETWEEN DEPOLARISING AND HYPERPOLARISING BIPOLAR CELLS TEMPORAL PROCESSING • BY AMACRINE CELLS AT SYNAPSE BETWEEN BIPOLAR CELL WITH GANGLION CELL • ADJUST THE BIPOLAR CELL IN NEGATIVE FEEDBACK ARRANGEMENT • AMACRINE CELLS PRODUCE DEPOLARISING POTENTIAL
- 26. GANGLION CELLS W GANLIONCELLS X GANGLION CELLS (SUSTAINED CELLS) Y GANGLION CELS (TRANSIENT CELLS) 40% 55% 5% SMALL SIZE MEDIUM SIZE LARGE SIZE DENDRITES WIDESPREAD – BRAOD FIELD SMALL FIELD MAXIMUM BROAD DENDRITIC FIELD MAXIMUM EXCITATION FROM RODS TRANSMITTED FROM BIPOLAR AND AMACRINE CELLS- ROD VISION IN DARK AND DETECTING DIRECTIONAL MOVEMENT RECEIVE INPUT FROM AT LEAST ONE CONE CELLS-COLOUR VISION REPOND TO RAPID CHANGES IN VISAUL IMAGES AND LIGHT INTENSITY
- 27. TRANSMISSIION OF IMPULSEIN THE VISUAL PATHWAY
- 28. RECEPTIVE FIELD- SINGLEOPTIC NERVE FIBRE CAN BE EXCITED ONLY BY SPECIFIC STIMULUS FALLING ON AREA SPECIFIC AREA ON RETINA LATERAL GENICULATE BODY • RELAY STATION-GENICULHYPERCLCARINE TRACT • SIGNALS FFROM TWO EYES ARE KEPT APART IN LGB • GATE THE TRANSMISSION OF SIGALS BY GETTING SIGNALS(INHIBITORY) FROM CORTIFUGAL FIBRES FROM VISUAL CORTEX RETICULAR FORMATION FROM MESENCEPHALON MAGNOCELLULAR LAYER • RECEIVE FROM Y GANGLION CELLS • PROVIDES RAPIDLY CONDUCTING PATHWAY • CARRY SIGNALS FOR DETECTION OF MOVEENT • COLOUR BLIND • NEGATIVE FOR POINT TO POINT TRANMSISSION PARVOCELLULAR CELLS • RECEIVE FROM X GANGLION CELLS • TRANSMIT COLOUR VISION • GOOD POINT TO POINT SPATIAL TRANSMISISON • TEXTURE, SHAPE AND DEPTH VISION
- 30. OPTIC RADIATIONS • COMPOSEDOF AXONS OF LGB WHICH PROJECT INTO THE VISUAL CORTEX • ARRANGEMENT OF FIBRES IN OPTIC RADIATIONN
- 31. ANALYSIS OF VISUAIMPULSE IN VISUAL CORTEX PRIMARY VISUAL CORTEX(BROADMANN AREA 17)- STRIATE CORTEX SECONDARY VISUAL CORTEX(BROADMANN AREA 18,19)- VISUAL ASSOCIATION AREAS ANTERIOR,SUPERIOR AND INFERIOR TO PRIMARY VISUAL CORTEX
- 32. CONTRALERAL STRIATE CORTEX RECIPROCALCONTRALERAL STRIATE CORTEX EXTRASTRIATE VISUAL CORTEX CONNECTIONS OF PRIMARY VISUAL CORTEX
- 33. RECEPTIVE FIELD OFVISUAL CORTEX CORTICAL CELL AS THREE RECEPTIVE FIELD TYPES • SIMPLE • COMPLEX • HYPERCOMPLEX SIMPLE CELLS • IN LAYER 4 OF PRIMARY VISUAL CORTEX • FORM THE FIRST RELAY STATION IN VISUAL CORTEX • RESPOND TO BAR OF LIGHT , LINES OR EDGES HAVING PARTICULAR ORIENTATION • RECEPTIVE FILED AXIS ORIENTATION- ORIENTATION OF STIMULUS MOST EFFECTIVE IN EVOKING RESPONSE • RECEPTIVE FIELD ARE ARRANGED IN PARALLEL BANDS OF ON AREAAND OFF AREAS • RECEPTIVE FIELDS HAVE CENTRAL BAND THAT IS EITHER AN ON REGION OR OFF REGION WITH PARALLEL FLANKING REGION ON TWO SIDES THAT ARE OPPOSITE • ROLE IN DETECTION OF LINES,BORDERS,ORIENATION OF LINE AND BORDER THAT IS VERTICAL, HORIZONTAL,INCLINATION,ETC
- 34. COMPLEX CELLS • INCORTICAL LAYERS BELOW AND ABOVE LAYER 4 OF AREAS 17,18,19 • REQUIRE PREFERRED ORIENTATION OF THE STIMULUS BUT LESS DEPEMDENT OF LOCATION OF STIMULUS IN VISUAL FIELD • RESPOND MAXIMALLY WHEN LINEAR STIMULUS IS MOVED LATERALLY WITHOUT CHANGE IN ORIENTATION • COMPLEX CELLS RECEIVE INPUTS FROM BOTH EYES AND ARE BINOCULAR • SIMPLE AND COMPLEX CELLS TOGETHER ARE KNOWNAS FEATURE DETECTORS HYPERCOMPLEX CELLS • IN CORTICAL LAYERS 2,3 OF CORTICAL AREA 17,18,19 • RETAIN PROPERTIES OF COMPLEX CELLS WITH FEATURE OF LINE STIMULUS REQUIRED TO BE OF SPECIFIC LENGTH • ROLE OF DETECTING LINES OF SPECIFIC LENGTH,ANGLES,SHAP
- 35. COLUMNAR ORGANISATION OFSTRIATE CORTEX • VERTICAL GROUPING OF CELLS WITH IDENTICAL ORIENTATION SPECIFICITY • VISUAL CORTEX IS ORGANISED STRUCTURALLY IN MANY VERTICAL COLUMNS OF NEURONL CELLS • SEQUENTIAL CHANGES IN ORIENTATION PREFERENCES OF 10 DEGRESS FROM COLUMN TO COLUMN ACROSS THECORTEX • FOR EACH GANGLION CELL RECEPTIVE FIELD IN THE VISUAL CORTEX,THERE IS COLLECTION OF COLUMN IN A SMALL AREA OF VISUAL CORTEX REPRESENTING THE POSSBLE PREFERRED ORIENTATION AT SMALL INTERVALS
- 37. COLOUR BLOBS • INPRIMARY VISUAL CORTEX • RESPOND SPECIFICALLY TO COLOUR SIGNALS ROLE OF EXTRASTRIATE CORTEX IN VISUA FUNCTIONS • INFORMATION FROM STRIATE CORTEX NEUROS (AREA 17 OR V1) GOES TO NEURONS IN ARE 18(V2),19(V2),V3,V4.MT • FIBRES FROM EXTRASTRIATE AREA GO BACK TO STRIATE CORTEX,THEY ARE CONNECTED TO EACH OTHER AND ALSO RECEIVE VISUAL INPUT FROM PILVINAR • THESE CELLS RECEIVING INFORMTON FROM FEATURE DETECTORS ARE CALLED PONTIFOCAL CELLS • COLOUR PROCESSING AREAS- V4 • MOVEMENT PROCESSING AREA –MT (MIDDLE PORTION TEMPORAL LOBE) • STEREOSCOPIC DEPTH PERCEPTION AREA-V2,V3
- 38. THREE PART SYSTEMHYPOTHESIS OF VISUAL PERCEPTION • FIRST SYSTEM- CONCERNED WITH PERCEPTION OF MOVEMENT,LOCATION AND SPATIAL ORGANISATION • SECOND SYSTEM-PERCEPTION OF COLOUR • THIRD- PERCEPTION OF SHAPE • INFORMTION FROM SYSTEMS IS INTEGRATED INTOASINGLE VISUAL PERCEPTION
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