midterm 2 - Lecture 6 slide 1 Fig 11.2Accommodation distant...

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Lecture 6, slide 1 Fig 11.2- Accommodation- distant objects lens is thin and flat For near vision lens is thick and rounder Controlled by ciliary muscles Lens held in place by zonule fibers Shape of lens determined by elasticity of lens – which keeps it rounded and tension exerted by zonule fibers- which keeps it flat fig 11.3- inner surface of retina- fundus optic disk/ papilla- where blood vessels enter eye, where ganglion cells axons leave retina to form optic nerve- no photoreceptors- “blind spot” macula lutea- contains yellow pigment- near center of retina- fine details- greatest acuity at fovea fig 11. 5 structure of retina three neuron chain—photoreceptor to bipolar cell to ganglion cell absorption of light- phototransduction cell bodies of photoreceptors make up outer nuclear layer, cells bodies of bipolar cells are in inner nuclear layer, synapse is in outer plexiform layer, bipolar cells synapse on ganglion cells in inner plexiform horizontal cells processes in outer plexiform layer- lateral interactions between photoreceptors and bipolar cells- to control sensitivies and stuff amacrine cell have processes in inner plexiform layer- between bipolar cells and ganglion cells- several functions- direction fig 11. 7- photoreceptors do not exhibit action potentials, light activation changes membrane potential which changes the rate of transmitter release shining light leads to membrane hyperpolarization in dark when photoreceptors are depolarized many Ca++ channels are open, so more release of transmitters; but when it is light, photoreceptor is hyperpolarized, so decrease in Ca++ channel so less transmitter released. In the dark- Na+ and Ca++ channels (inward, depolarizing) are gated by cGMP, which is balanced by K+ efflux channels- which hyperpolarizes Fig 11.8- absorption of light leads to a decrease of cGMP levels, closing cation (Na+, Ca++) channels and hyperpolarizes Fig 11.9- photopigment absorbs photon- photopigment contains retinal coupled to proteins called opsins. Rhodopsin- photopigment in rods Retinal rests in opsins in outersegment of membrane When retinal absorbs a photon of light one of the doubles bonds changes so that the molecule changes from 11-cis isomer to all-trans retinal- which changes the opsin, which activate an intracellular messenger called transducin, which activates phosphodiesterase (PDE) which hydrolyzes cGMP and closes the channel
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Great signal amplification- 1 activated rhodopsin can activate 800 transducin molecules Activated rhodopsin is phosphorylated by rhodopsin kinase which allows arrestin to bind to rhodopsin, which blocks rhodopsin from activating transducin and blocks the phototransduction cascade Fig 11.10 Retinoid cycle- all-trans retinal dissociates from opsin and diffuses into cytosol, and it is converted to all-trans retin ol , and transported into pigment epithelium by chaperone protein- interphotoreceptor retinoid binding protein (IRBP)- where it is converted to 11- cis retinal Light adaptation- magnitude of phototransduction amplification
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This note was uploaded on 10/14/2010 for the course BIOLOGY bipn 142 taught by Professor Aaron during the Spring '10 term at UCSD.

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midterm 2 - Lecture 6 slide 1 Fig 11.2Accommodation distant...

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