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ELAINE N. MARIEB EIGHTH EDITION 8 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings PowerPoint ® Lecture Slide Presentation by Jerry L. Cook, Sam Houston University ESSENTIALS OF HUMAN ANATOMY & PHYSIOLOGY PART A Special Senses
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Senses Special senses Smell Taste Sight Hearing Equilibrium General senses of touch Temperature Pressure Pain
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Eye and Vision 70 percent of all sensory receptors are in the eyes Each eye has over a million nerve fibers Protection for the eye 1.Most of the eye is enclosed in a bony orbit 2.A cushion of fat surrounds most of the eye
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Accessory Structures of the Eye Eyelids Eyelashes Conjunctiva Lines the eyelids Connects to the surface of the eye Secretes mucus to lubricate the eye Figure 8.1b
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Accessory Structures of the Eye Lacrimal apparatus 1.Lacrimal gland – produces lacrimal fluid 2.Lacrimal canals – drains lacrimal fluid from eyes 3.Lacrimal sac – provides passage of lacrimal fluid towards nasal cavity Figure 8.1a
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Function of the Lacrimal Apparatus Properties of lacrimal fluid Dilute salt solution (tears) Contains antibodies and lysozymes (enzymes) Protects, moistens, and lubricates the eye Empties into the nasal cavity
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings External Eye Muscles 6 Muscles attach to the outer surface of the eye Produce eye movements Figure 8.2
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Structure of the Eye The wall is composed of three tunics ( layers ) 1.Fibrous tunic – outside layer 2.Choroid – middle layer 3.Sensory tunic – inside layer Figure 8.3a
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Fibrous Tunic Sclera “white of the eye” Cornea Transparent, central anterior portion Allows for light to pass through Repairs itself easily/quickly, but contains a lot of pain receptors The only human tissue that can be transplanted without fear of rejection
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Choroid Layer Blood-rich nutritive layer Cilliary body – made of smooth muscle Iris Pigmented layer that gives eye color Pupil – rounded opening in the iris to allow light in
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sensory Tunic (Retina) Contains photoreceptors Rods Cones Messages leave the retina through the optic nerve
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
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Neurons of the Retina and Vision Rods Most are found towards the edges of the retina Allow dim light vision and peripheral vision Perception is all in gray tones Cones Allow for detailed color vision Densest in the center of the retina Fovea centralis – area of the retina with only cones No photoreceptor cells are at the optic disk, or blind spot
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Could you be colorblind? What can you see here?
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Could you be colorblind? What can you see here?
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Internal Eye Fluids Aqueous humor Watery fluid found in chamber between the lens and cornea Similar to blood plasma Helps maintain intraocular (inner eye) pressure Provides nutrients for the lens and cornea Vitreous humor Gel-like substance behind the lens Keeps the eye from collapsing Lasts a lifetime and is not replaced
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Lens Biconvex crystal-like structure Biconvex Held in place by a suspensory ligament attached to the ciliary body (iris) Figure 8.3a
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Lens Accommodation Light must be focused to a point on the retina for optimal vision The eye is set for distance vision (over 20 ft away) The lens must change shape to focus for closer objects Figure 8.9
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Lens Accommodation
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Eye Reflexes Internal muscles are controlled by the autonomic nervous system Bright light causes pupils to constrict Viewing close objects causes accommodation (changing shape of the lens) External muscles control eye movement to follow objects Viewing close objects causes convergence (crossed eyed)
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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Eye diseases/disorders Conjunctivitis - an inflammation of the conjunctiva; different causes, including: Viruses, bacteria, irritants such as shampoos, dirt, smoke, and pool chlorine, allergies, like dust, pollen, or a special type of allergy that affects some contact lens wearers Conjunctivitis Cataracts - cloudy area in the lens of the eye that blocks the Cataracts passage of light to the retina; Aging and exposure to sunlight can cause cataracts and may appear after an eye injury Glaucoma- too much fluid pressure builds up inside of the eye and the increased pressure can damage the optic nerve, which transmits images to the brain Glaucoma- Macular Degeneration - occurs when the small central portion of the retina (macula) deteriorates
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