Effect of Light on Rods

Effect of Light on Rods - * Rods and cones contain many Na...

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Anatomy of the Eye Effect of Light on Rods * Rods are activated when light produces chemical change in rhodopsin. * Bleaching reaction: * Rhodopsin dissociates into retinene (rentinaldehyde) and opsin. * 11-cis retinene is converted to all-trans form. * Initiates changes in ionic permeability to produce AP in ganglionic cells. * Provide black-and-white vision. Dark Adaptation * Gradual increase in photoreceptor sensitivity when entering a dark room. * Maximal sensitivity reached in 20 min. * Increased amounts of visual pigments produced. * Slight increased pigment in cones. * Greater increased rhodopsin in rods. * 100,00-fold increase in light sensitivity in rods. Electrical Activity of Retinal Cells * Ganglion cells and amacrine cells are only neurons that produce AP. * In dark, photoreceptors release inhibitory NT that hyperpolarizes bipolar neurons. * Light inhibits release of inhibitory NT. * Dark current:
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Unformatted text preview: * Rods and cones contain many Na + channels that are open in the dark. * Causes slight membrane depolarization in dark. Electrical Activity of Retinal Cells * Na + channels rapidly close in response to light. * cGMP required to keep the Na + channels open. * Opsin dissociation causes the alpha subunits of G-proteins to dissociate. * G-protein subunits bind and activate phosphodiesterase, converting cGMP to GMP. * Na + channels close when cGMP converted to GMP. Cones and Color Vision * Cones less sensitive than rods to light. * Cones provide color vision and greater visual acuity. * High light intensity bleaches out the rods, and color vision with high acuity produced by cones. Cones and Color Vision * Trichromatic theory of color vision: * 3 types of cones: * Blue, green and red. * According to the region of visual spectrum absorbed....
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This note was uploaded on 01/29/2012 for the course SCIE SYG2000 taught by Professor Bernhardt during the Fall '10 term at Broward College.

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