17Su11Lec4.1 - COGS17 Neurobiology of Cognition Summer 2011...

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COGS17 Neurobiology of Cognition Summer 2011 Lecture 4.1: Vision The Retina – Composed of Neurons (except Pigment Epithelium), multi-layered, covering rear, inner wall of eyeball - Receptors molecules that react to light (“isomerize”) >> alter release of NT - Receptors show Spontaneous Potentials (more light, more change in release of NT – see below) - Rods : larger, in periphery, ~120 million/eye - Cones : smaller, dispersed throughout retina, ~6 million/eye - Fovea - small central area of high concentration of Cones only ; for high detail resolution - Bipolars - Postsynaptic to Receptors, show Spontaneous firing, Graded Potentials - Ganglions - Postsynaptic to Bipolars, Show Action Potentials ; Axons of the Ganglion Cells form the Optic Nerve => brain - Blind Spot or “Optic Disk ” - where Optic Nerve leaves eye & blood vessels enter/leave; No Receptors there - Interneurons - perpendicular to pathway, influence interactions between the above neurons: - Horizontals – Graded Potentials, mostly Inhibitory NT , modify interface of Receptors and Bipolars - Amacrines – Graded Potentials, mostly Inhibitory NT , modify interface of Bipolars and Ganglions ; Many kinds - Pigment Epithelium - rearmost layer of (Non-Neural ) cells; feeds & recycles from receptors; helps reflect/maximize light See Supplement to Vision Lecture Isomerization = Converting light into a neural signal - Outer Segment of Receptors composed of lamellae w/embedded Photopigment molecules that react to light, made of … -1) Opsin : long protein chain (150 X as large as…) -2) Retinal : short lipid segment, synthesized from Vitamin A - 11-Cis Retinal absorbs photon of light, changes shape (straightens, now called All-trans Retinal) and detaches from Opsin - Opsin changes color from reddish-purple to pale yellow (“bleached”) - This activates Second Messengers in Receptor that lead to ion gates closing, modifying graded release of NT - Each Rod has ~10 mil photopigment molecules, called Rhodopsin; Cones have less photopigment, their own variants - Photopigment Regeneration (recombination of Retinal & Opsin), using enzymes from Pigment Epithelium, Requires time - e.g. Hard to see indoors at first after bright sunlight (since “Light Adapted ”) but as regenerate, sensitivity restored - e.g. Hard to see just after turn off lights, but soon, as more regenerate, sensitivity increased (become “Dark Adapted
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This note was uploaded on 09/07/2011 for the course COGS 17 taught by Professor Pineda during the Spring '06 term at UCSD.

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17Su11Lec4.1 - COGS17 Neurobiology of Cognition Summer 2011...

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