1. The Senses General senses of touch –Temperature –Pressure –Pain Special senses –Smell –Taste –Sight –Hearing –Equilibrium

2. The Eye and Vision 70 percent of all sensory receptors are in the eyes Each eye has over a million nerve fibers The eye is a sphere about 1 inch in diameter…like a ping pong Only 1/6 of the eye is seen –Most of the eye is surrounded by bone & cushioned by fat

3. Accessory Structures of the Eye Eyelids Eyelashes Muscles Figure 8.1b

4. muscles

5. Accessory Structures of the Eye Conjunctiva –Membrane that lines the eyelids –Connects to the surface of the eye & secretes mucus for lubrication

6. Homeo Imbalance –Conjunctivitis = reddened irritated eyes. “Pinkeye” is the HIGHLY infectious form caused by bacteria or virus

7. Accessory Structures of the Eye Lacrimal apparatus –Lacrimal gland – produces diluted salt solution (tears) –Lacrimal canals – drains tears from eyes –Lacrimal sac – provides passage of tears towards nasal cavity Figure 8.1a

8. Properties of lacrimal fluid (AKA TEARS!) –Dilute salt solution which contains lysozyme an anti-bacterial protein Protects, moistens, and lubricates the eye Empties into the nasal cavity

9. Nasolacrimal duct – empties tears into the nasal cavity (connects eye with nose) –Crying makes you sniffle

10. Homeo Imbalance –A cold or allergies can cause the lacrimal duct to swell shut. This stops drainage of tears and you get watery eyes.

11. Structure of the Eye The wall is composed of three tunics (layers) –Fibrous tunic – outside layer –Choroid – middle layer –Sensory tunic – inside layer Figure 8.3a

12. The Fibrous Tunic Sclera –White connective tissue layer Cornea –Transparent allows light to pass through –Vulnerable to damage but repairs itself easily –The only human tissue that can be transplanted without fear of rejection (no blood=no antibodies)

13. Choroid Layer Blood-rich nutritive tunic Pigment dark in color prevents light from scattering Modified interiorly into two structures –Cilliary body – smooth muscle, focuses lens for clear vision –Iris- smooth muscle, regulates amount of light that enters Pigmented layer that gives eye color Pupil – rounded opening in the iris

14. Sensory Tunic (Retina) Contains millions of receptor cells called photoreceptors –Rods & Cones Signals pass from photoreceptors to retina Signals leave the retina toward the brain through the optic nerve

15. Homeo Imbalance –Retinal Detachment: Retina separates from choroid. Retina cannot get nutrients and can die. Easily fixed with laser surgery. –Caused by violent motion of the head, genetics

16. Lens Biconvex crystal-like structure Held in place by a ligament attached to the ciliary body Figure 8.3a

17. The lens divides the eye into 2 segments or chambers Homeo Imbalance –Cataracts: Occur as we age. The lens becomes hard and opaque

18. Internal Eye Chamber Fluids Aqueous humor –Watery fluid found in chamber between the lens and cornea –Maintains intraocular pressure –Provides nutrients for the lens and cornea

19. Homeo Imbalance –If the aqueous humor cannot drain, pressure in the eye increases dramatically. –This leads to glaucoma, which will become painful and possibly lead to loss of sight. –Early detection is key since a lot of damage can be done w/o pain. The machine that blows on your eye!

20. Internal Eye Chamber Fluids Vitreous humor –Gel-like substance behind the lens that fills the eyeball –Lasts a lifetime and is not replaced (can be floaters)

21. Neurons of the Retina and Vision Rods –Most are found towards the edges of the retina –Allow dim light & peripheral vision – all in gray tones Cones –Allow for detailed color vision –Densest in the center of the retina

22. Cone Sensitivity There are 3 types of cones each sensitive to different wavelengths Total Color blindness is the result of lack all cone types. Partial is due to lack of 1 or 2 types. Figure 8.6

23. Lens Accommodation Light is bent or refracted as it enters the eye The lens changes shape so that the light is focused on the retina The ability to focus on objects closer is called accommodation As objects come closer the lens bulges

24. Vision Problems Perfect vision is called emmetropia or “harmonious vision” Nearsightedness- you can see up close but not far away. Picture focuses in front of retina Farsightedness- you can see far away but not close up. Picture focuses behind retina.

25. Images Formed on the Retina The image on the retina is reversed, upside-down and smaller Figure 8.10

26. http://video.about.c om/vision/LASIK- Eye-Surgery.htmhttp://video.about.c om/vision/LASIK- Eye-Surgery.htm

27. Visual Pathway Optic nerve: carry impulses from retina to brain, Part of each optic nerve crosses at the optic chiasma –Each side of brain receives info from both eyes –Allows for binocular vision & depth perception Figure 8.11

28. http://www.peteducation.com/article.cfm?c =17+1797&aid=1596http://www.peteducation.com/article.cfm?c =17+1797&aid=1596

29. http://www.youtube.com/watch?v=38PGB 9dcr4chttp://www.youtube.com/watch?v=38PGB 9dcr4c Perspective on the 5 senses