Visual System II: Retinal Processing. Adequate Stimulus: A stimulus of a quality and of sufficient intensity to excite a sensory receptor. Adequate Stimulus.

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Presentation transcript:

Visual System II: Retinal Processing

Adequate Stimulus: A stimulus of a quality and of sufficient intensity to excite a sensory receptor. Adequate Stimulus for Visual System: Electromagnetic wave with a wavelength between 350 and 750 nm and of sufficient intensity to excite a photoreceptor.

100μm B A

Fovea cones Periphery rods cones

rhodopsin 11-cis retinal + opsin all-trans retinal + opsin 11-cis retinal All-trans retinal opsin

When light strikes photoreceptor  activates G-protein  activates c-GMP phosphodiesterase  c-CMP hydrolyzed to 5-GMP  c-GMP dependent cation channels close  reduced Na + and C 2+ currents  hyperpolarization of cell  reduces release of glutamate In dark, cGMP keeps cation (mainly Na + ) channels open. The inward Na + “dark current” keeps the resting membrane potential at about -40 mv. This depolarization keeps voltage-gated Ca2+ channels open, resulting in release (“dripping “)of glutamate from the photoreceptor.

bipolar cells amacrine cells ganglion cells horizontal cells photoreceptors rods cones

direct vs. indirect pathways to ganglion cells

visual receptive fields

fovea periphery

Receptive field size about mm diam. Receptive field size about 1.0 mm diam