Nervous System - Sensory

Horizontal and amacrine cells provide lateral

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Unformatted text preview: Photoreceptors: rods and cones The outer layer of the retina picks up the information from the rods and cones, transmits. The rods and cones are the photoreceptors, communicate with the bipolar cells. Horizontal cells, like the true bipolar cells which communicate via graded potentials The communicate with the ganglion cells, that are the endings of the optic nerve. Horizontal and amacrine cells provide lateral modulation, light passes through inner and middle of retina These ganglion cells are the first place where and AP occurs. The Distribution of Rods and Cones The Fovea, the focal point of light when on object is in sight right in front, has the highest distribution of cones for color vision Peripheral tends to be black and white. The Outer egment of the rods and cones receives the light, but the inner segment creates graded potentials. Phototransduction: Dark Adaptation Conversion of light energy to nerve signals 4 Photopigments: retinal and opsin 4 opsins: 1 in rods (black/white), 3 in cones (color vision) In the dark, more transmitter is produced. More cGMP is produced, an open state if you will Light Adaptation Here cGMP is broken down, and thus no longer available to affect the NA channels, no depolarization (maybe even hyperpolarization), so no graded potential is made. The receptor field for cones is quite small Rods have a large receptor field Adaptation to Light and Dark: Small changes in light intensity pupillary dilation and constriction Larger changes in light intensity changes in photopigments Light “bleaches” rods, opsin separated from retinal, no light attached Move to dark: Sensitivity of rods low due to previous bleaching Retinal and opsin reassociate Can again detect dim light Dark maintains rods in sensitive state, opsin/retinal associated, light absorbed Move to bright light: Sensitive rods overwhelmed...
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