1. Essentials of Human Anatomy & Physiology Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slides 8.1 – 8.19 Seventh Edition Elaine N. Marieb Chapter 8 Special Senses Lecture Slides in PowerPoint by Jerry L. Cook

2. The Senses Slide 8.1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  General senses of touch  Temperature  Pressure  Pain  Special senses  Smell  Taste  Sight  Hearing  Equilibrium

3. The Eye and Vision Slide 8.2 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  70 percent of all sensory receptors are in the eyes  Each eye has over a million nerve fibers  Protection for the eye  Most of the eye is enclosed in a bony orbit  A cushion of fat surrounds most of the eye

4. Some things you may not know about your eyes... The average blink lasts for about 1/10th of a second. While it takes some time for most parts of your body to warm up to their full potential, your eyes are on their “A game” 24/7. Eyes heal quickly. With proper care, it only takes about 48 hours for the eye to repair a corneal scratch. Seeing is such a big part of everyday life that it requires about half of the brain to get involved. Newborns don’t produce tears. They make crying sounds, but the tears don’t start flowing until they are about 4-13 weeks old. Around the world, about 39 million people are blind and roughly 6 times that many have some kind of vision impairment. Doctors have yet to find a way to transplant an eyeball. The optic nerve that connects the eye to the brain is too sensitive to reconstruct successfully.

5. 1.You blink about 12 times every minute. 2.Some people are born with two differently colored eyes. This condition is heterochromia. Your eyes are composed of more than 2 million working parts. We all have microscopic creatures lurking in our eyelashes. Only 1/6 of your eye is exposed to the outside world. It is 2.5 cm in length and weighs about 7 grams. Your eyes begin to develop 2 weeks after conception. The entire length of all the eyelashes shed by a human in their life is over 98 feet. When you blink, you shut your eyes for 0.3 seconds. That’s a total of 30 minutes each day!

6. Myth: Reading in dim light is harmful to your eyes.

7. Accessory Structures of the Eye Slide 8.3a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Eyelids  Eyelashes Figure 8.1b

8. Accessory Structures of the Eye Slide 8.3b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Meibomian glands – modified sebacious glands produce an oily secretion to lubricate the eye Figure 8.1b

9. Accessory Structures of the Eye Slide 8.3c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Ciliary glands – modified sweat glands between the eyelashes Figure 8.1b

10. Accessory Structures of the Eye Slide 8.4a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Conjunctiva  Membrane that lines the eyelids  Connects to the surface of the eye  Secretes mucus to lubricate the eye

11. Accessory Structures of the Eye Slide 8.4b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Lacrimal apparatus  Lacrimal gland – produces lacrimal fluid  Lacrimal canals – drains lacrimal fluid from eyes Figure 8.1a

12. Accessory Structures of the Eye Slide 8.4c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Lacrimal sac – provides passage of lacrimal fluid towards nasal cavity Figure 8.1a

13. Accessory Structures of the Eye Slide 8.4d Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Nasolacrimal duct – empties lacrimal fluid into the nasal cavity Figure 8.1a

14. Function of the Lacrimal Apparatus Slide 8.5 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Properties of lacrimal fluid  Dilute salt solution (tears)  Contains antibodies and lysozyme  Protects, moistens, and lubricates the eye  Empties into the nasal cavity

15. Extrinsic Eye Muscles Slide 8.6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Muscles attach to the outer surface of the eye  Produce eye movements Figure 8.2

16. Structure of the Eye Slide 8.7 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  The wall is composed of three tunics  Fibrous tunic – outside layer  Choroid – middle layer  Sensory tunic – inside layer Figure 8.3a

17. The Fibrous Tunic Slide 8.8 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Sclera  White connective tissue layer  Seen anteriorly as the “white of the eye”  Cornea  Transparent, central anterior portion  Allows for light to pass through  Repairs itself easily  The only human tissue that can be transplanted without fear of rejection

18. Choroid Layer Slide 8.9 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Blood-rich nutritive tunic  Pigment prevents light from scattering  Modified interiorly into two structures  Cilliary body – smooth muscle  Iris  Pigmented layer that gives eye color  Pupil – rounded opening in the iris

19. Sensory Tunic (Retina) Slide 8.10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Contains receptor cells (photoreceptors)  Rods  Cones  Signals pass from photoreceptors via a two-neuron chain  Bipolar neurons  Ganglion cells  Signals leave the retina toward the brain through the optic nerve

20. Neurons of the Retina Slide 8.11 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.4

21. Neurons of the Retina and Vision Slide 8.12a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Rods  Most are found towards the edges of the retina  Allow dim light vision and peripheral vision  Perception is all in gray tones

22. Neurons of the Retina and Vision Slide 8.12b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  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

23. Cone Sensitivity Slide 8.13 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  There are three types of cones  Different cones are sensitive to different wavelengths  Color blindness is the result of lack of one cone type Figure 8.6

24. Lens Slide 8.14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Biconvex crystal-like structure  Held in place by a suspensory ligament attached to the ciliary body Figure 8.3a

25. Internal Eye Chamber Fluids Slide 8.15a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Aqueous humor  Watery fluid found in chamber between the lens and cornea  Similar to blood plasma  Helps maintain intraocular pressure  Provides nutrients for the lens and cornea  Reabsorbed into venous blood through the canal of Schlemm

26. Internal Eye Chamber Fluids Slide 8.15b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Vitreous humor  Gel-like substance behind the lens  Keeps the eye from collapsing  Lasts a lifetime and is not replaced

27. Lens Accommodation Slide 8.16 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  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

28. Images Formed on the Retina Slide 8.17 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.10

29. Visual Pathway Slide 8.18a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Photoreceptors of the retina  Optic nerve  Optic nerve crosses at the optic chiasma Figure 8.11

30. Visual Pathway Slide 8.18b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Optic tracts  Thalamus (axons form optic radiation)  Visula cortex of the occipital lobe Figure 8.11

31. Eye Reflexes Slide 8.19 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Internal muscles are controlled by the autonomic nervous system  Bright light causes pupils to constrict through action of radial and ciliary muscles  Viewing close objects causes accommodation  External muscles control eye movement to follow objects  Viewing close objects causes convergence (eyes moving medially)