1. Special Senses

2. Sight- Eyes

3. The Sense of Sight Accessory organs:
Eyelids- 4 layers: skin, muscle, connective tissue, conjunctiva (mucous membrane) moved by orbicularis oculi muscles (close) and levatator palpebrae superioris (open)

4. Lacrimal apparatus- lacrimal gland- secretes tears continuously– tears contain lysozyme which protects against bacteria

5. 6 extrinsic muscles- movement of eye

6. Structure of the Eye Cornea Helps focus entering light rays
Connective tissue with thin layer of epithelium
No blood vessels
Unusually regular fiber pattern

7. Sclera (white of eye)
Opaque due to large, disorganized collagenous and elastic fibers
For protection and attachment

8. Choroid coat
Contains blood vessels
Produces melanin which absorbs excess light

9. Ciliary body
Forms internal ring around front of eye (muscle fibers and ligaments)

10. Iris
Colored portion of eye (pigmented versus non-pigmented)
Thin diaphragm composed of connective tissue and muscle fibers
Circular and radial muscle fibers control size of pupil (stimulated by photons of light)

11. Aqueous humor
Fills space between cornea and lens
Nourishes, helps hold shape

12. Glaucoma- aqueous humor made quicker than can be removed; pressure builds, damage results

13. Lens
Lies directly behind iris and pupil
Epithelial cells (cytoplasm is transparent part)
Change shape to focus

14. Cataract- fluid in lens becomes cloudy and opaque

15. Vitreous humor-
holds the shape
of the back of the eye

16. Light entering the eye is refracted

18. Retina- contains photoreceptors
Rods- more sensitive in low light, gives general outline, seen as black and white
Cones- less sensitive in low light, sharp picture, color

19. Fovea- cones only, sharpest vision

20. Optic disk- where nerve fibers from retina enter optic nerve
Known as the “blind spot”

21. Night blindness- fewer working rods (lack of vitamin A)
Day blindness- lack of working cones

22. Visual pigments
In rods- rhodopsin breaks down into opsin and retinal when struck by photons. This initiates a chemical rxn (action potential) which is sent to the visual cortex. (occipital lobe)
In bright light nearly all rhodopsin is broken down, reducing rod sensitivity

23. In cones- 3 different light sensitive proteins connected to retinal
Depending on which one is stimulated, brain interprets that color
Erythrolabe- red
Chlorolabe- green
Cyanolabe- blue

24. If all are stimulated at once- white

25. 1. Normal Color Vision: A: 29, B: 45, C: --, D: 26
4 Sex-Linked Traits:
 1. Normal Color Vision:  A: 29,  B: 45,  C: --,  D: 26
 2. Red-Green Color-Blind:  A: 70,  B: --,  C: 5,  D: --
 3. Red Color-blind:  A: 70,  B: --,  C: 5,  D: 6
 4. Green Color-Blind:  A: 70,  B: --,  C: 5,  D: 2

26. A few enter the thalamus to stimulate visual reflexes
Axons of the retina form optic nerves which join at optic chiasma in which certain fibers cross (medial) and other fibers do not (lateral)
A few enter the
thalamus to stimulate
visual reflexes

27. Hearing- Ears
Also static and dynamic equilibrium

28. Outer Ear Composed of auricle (“ear”) and meatus (auditory canal)
collects and directs
sound waves
ends at tympanic
membrane (ear drum)
glands secrete cerumen

29. Middle Ear Small air-filled, mucosa-lined cavity within temporal bone
transfers vibrations via the malleus (hammer),
incus (anvil) and stapes (stirrup)
pressure needs to be equalized

30. Inner (internal) Ear Maze of bony labyrinth (cavity): cochlea (spiral)
vestibule
semicircular canals
Filled with fluid
Lined with mechanoreceptors- hair cells
Cochlear nerve sends info to temporal lobe
(auditory cortex)
Maculae receptors report changes of position
(static equilibrium)- with tiny stones
Bending of cupula indicates rotation
(dynamic equilibrium)

32. Smell- Olfactory bulbs
Chemical sense-
chemoreceptors called
olfactory receptors
Thousands of smells
Very sensitive- adapt quickly
Pathways closely tied to limbic system

33. Taste- Taste buds Replaced every 7-10 days!! Five basic tastes: sweet,
sour, bitter, salty, and umami
Taste tied to smell