Chapter 15 Special Senses Part 2

Chapter 15 Special Senses Part 2 - Special Senses Part 2...

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Special Senses Part 2
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Light Electromagnetic radiation – all energy waves from short gamma rays to long radio waves Our eyes respond to a small portion of this spectrum called the visible spectrum Different cones in the retina respond to different wavelengths of the visible spectrum
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Light Figure 15.10
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Refraction and Lenses When light passes from one transparent medium to another its speed changes and it refracts (bends) Light passing through a convex lens (as in the eye) is bent so that the rays converge to a focal point When a convex lens forms an image, the image is upside down and reversed right to left
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The spoon in this glass seems to be broken When light passes from one transparent medium to another its speed changes and it refracts (bends) Light passing through a convex lens (as in the eye) is bent so that the rays converge to a focal point
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Refraction and Lenses Figure 15.12a, b
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Focusing Light on the Retina Pathway of light entering the eye: cornea, aqueous humor, lens, vitreous humor, and the neural layer of the retina to the photoreceptors Light is refracted: At the cornea Entering the lens Leaving the lens The lens curvature and shape allow for fine focusing of an image
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http:// www.youtube.com/watch?v=CuVxujt9JX8
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Focusing for Distant Vision Light from a distance needs little adjustment for proper focusing Far point of vision – the distance beyond which the lens does Figure 15.13a
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Focusing for Close Vision Close vision requires: Accommodation – changing the lens shape by ciliary muscles to increase refractory power Constriction – the pupillary reflex constricts the pupils to prevent divergent light rays from entering the eye Convergence – medial rotation of the eyeballs toward the object being viewed
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Focusing for Close Vision Figure 15.13b
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Problems of Refraction Emmetropic eye – normal eye with light focused properly Myopic eye (nearsighted) – the focal point is in front of the retina Corrected with a concave lens Hyperopic eye (farsighted) – the focal point is behind the retina Corrected with a convex lens
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Problems of Refraction Figure 15.14a, b
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Photoreception: Functional Anatomy of Photoreceptors Photoreception – process by which the eye detects light energy Rods and cones contain visual pigments (photopigments) Arranged in a stack of disklike infoldings of the plasma membrane that change shape as they absorb light
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Figure 15.15a, b
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Rods Functional characteristics Sensitive to dim light and best suited for night vision Absorb all wavelengths of visible light Perceived input is in gray tones only Sum of visual input from many rods feeds into a single ganglion cell Results in fuzzy and indistinct images
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Cones Functional characteristics Need bright light for activation (have low sensitivity) Have pigments that furnish a vividly colored view Each cone synapses with a single ganglion cell Vision is detailed and has high resolution
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This note was uploaded on 01/06/2012 for the course BIOL 2401 taught by Professor Elainefanin during the Spring '11 term at Collins.

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Chapter 15 Special Senses Part 2 - Special Senses Part 2...

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