ch4 - vision the detection of light stimuli sensation in...

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- vision – the detection of light - stimuli – sensation in general is the detection of stimuli – it is energies from the world around us that affect us in some way - receptors – specialized cells that convert environmental energies into signals fro the nervous system - electromagnetic spectrum – the continuum of all the frequencies of radiated light - pupil – an adjustable opening in the eye through which light enters - iris – the colored structure on the surface of the eye, surrounding the pupil (when you describe what eye color you have) - light that passes thru the pupil travels thru the vitreous humor (a clear jellylike substance) to strike the retina at the back of the eyeball - retina – a layer of visual receptors covering the back surface - cornea – a rigid transparent structure on the outer surface of the eyeball, always focuses light in the same way - lens – a flexible structure that can vary in thickness, enabling the eye to accommodate to adjust its focus for objects at different distances o look at close object, eye muscles tighten and makes the lens thicker and rounder - fovea – the central area of the human retina – adapted for highly detailed vision, has the greatest density of receptors o when you want to see something in detail, you look at it directly so that light focuses on the fovea - presbyopia – impaired ability to focus on nearby objects bc of decreased flexibility of the lens - myopia – elongated eyeballs, nearsighted, difficulty focusing on distant objects - hyperopia – flattened eyeballs, farsighted, difficulty focusing on nearby objects - glaucoma – a condition characterized by increased pressure within the eyeball, result can damage optic nerve and therefore impair peripheral vision (tunnel vision) - cataract – a disorder in which the lens becomes cloudy; can replace with artificial lens but suffer increased risk of damage to retina from UV light - visual receptors of the eye, specialized neurons in the retina at the back of the eyeball, are so sensitive to light that they can respond to a single photon, the smallest possibly quantity of light o 2 types of visual receptors: cones and rods cones – adapted for color, daytime, and detailed vision of visual receptors, about 5% are cones rods – adapted for vision in dim light o proportion of cones is highest toward the center of the retina o away from the fovea, the proportion of cones drops sharply; for that reason you are colorblind in the periphery of your eye o rods are more effective than cones for detecting light for 2 reasons: a rod is slightly more responsive to faint stimulation than a cone is the rods pool their resources; only a few cones converge their messages onto the next cell, called a bipolar cell, whereas many rods converge their messages
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- the center of the retina consists entirely of cones; if you look slightly to the side of the star, the light falls on an area of the retina that consists partly of rods, which are more sensitive to faint light - -
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