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Chapter 6 - Chapter 6 Vision sensory receptors a...

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1Chapter 6: Vision •sensory receptors: a specialized neuron that detects a particular category of physical events •sensory transduction: the process by which sensory stimuli are transduced into slow, graded receptor potentials •receptor potential: a slow, graded electrical potential produced by a receptor cell in response to a physical stimulus The Stimulus •electromagnetic radiation with a wavelength of between 380 and 760 nm visible to us •hue: one of the perceptual dimensions of color; -the dominant wavelength •brightness: one of the perceptual dimensions of color; - intensity •saturation: one of the dimensions of color; -purity -if all radiation is of one wavelength, the perceived color is pure, or fully saturated •same hue, mid brightness and high saturation arrives at the truest color Anatomy of the visual system The eyes •vergence movement: the cooperative movement of the eyes, which ensures that the image of an object falls on identical portions of both retinas -convergence: looking at something close •Exaggerated convergence - cross eyed -divergence: looking at something far •saccadic movement: the rapid, jerky movement of the eyes used in scanning a visual scene -may be a way of allowing high quality resolution of a scene •pursuit movement: the movement that the eyes make to maintain an image of a moving object on the fovea -gaze shift -example: following finger with eye; slow, steady movements •blind spot- optic disk •accommodation: changes in the thickness of the lens of the eye, accomplished by the ciliary muscles, that focus images of near or distant objects on the retina •retina: the neural tissue and photoreceptive cells located on the inner surface of the posterior portion of the eye •rod: one of the receptor cells of the retina; sensitive to light of low intensity -black & white -in dim light we use rod vision •cone: one of the receptor cells of the retina; maximally sensitive to one of three different wavelengths of light and hence encodes color vision -much fewer cones than rods -daytime vision -provide us with info about -source of high sharpness -color vision
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-photoreceptors have ion channels that are normally open •Held open by cGMP •photoreceptor: one of the receptor cells of the retina; transduces photic energy into electrical potentials •fovea: the region of the retina that mediates the most acute vision of birds and higher mammals. Color-sensitive cones constitute the only type of photoreceptor found in the fovea •optic disk: the location of the exit point from the retina of the fibers of the ganglion cells that form the optic nerve; responsible for the blind spot •bipolar cell: a bipolar neuron located in the middle layer of the retina, conveying information from the photoreceptors to the ganglion cells •ganglion cell: a neuron located in the retina that receives visual information from bipolar ells; its axons give rise to the optic nerve •horizontal cell: a neuron in the retina that interconnects adjacent photoreceptors and the outer
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