1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sensory Tunic (Retina)  Contains photoreceptors  Rods  Cones  Messages leave the retina through the optic nerve

12. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

14. 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

15. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Could you be colorblind? What can you see here?

16. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Could you be colorblind? What can you see here?

17. 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

18. 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

19. 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

20. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Lens Accommodation

21. 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)

22. 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