Chapter 8 Special Senses
Part A: Vision
1. The eye and vision
a. 70% of all sensory receptors are in the eye
b. Each eye – over a million nerve fibers
2. Protection for the eye
a. A bony orbit
b. A surrounding cushion of fat
c. Accessory structures – not directly involved with actual vision
d. Eyelids and eyelashes: prevent some particles from getting into the eye
i. Tarsal (oil) glands: lubricate the eye
ii. Ciliary (sweat) glands: located between the eyelashes
e. Conjunctiva: membrane lines the eyelids
i. Connects to the surface of the eye
ii. Secretes mucus, lubricates eye
f. Lacrimal = tear apparatus
i. Gland: produces fluid
ii. Canals: drain fluid from the eye
iii. Sac: passage of fluid towards nasal cavity
iv. Nasolacrimal duct: empties fluid into nasal cavity
3. Functions
a. Protects, moistens, and lubricates the eye
b. Empties into the nasal cavity
4. Properties
a. Dilute salt solution (tears)
b. Contains antibodies and lysozyme (antibacterial)
c. Possibly contain hormones (anti-aggressive)
d. Extrinsic eye muscles: 6 muscles attach to the outer surface of the eye\
i. Produces eye movement
5. Layers forming wall of eyeball:
a. Fibrous outside layer
i. Sclera: “white of the eye” connective tissue
ii. Cornea: Transparent, central anterior portion
iii. Allows light to pass through
iv. Repairs itself easily
v. The only human tissue that can be transplanted without fear of rejection
b. Vascular middle layer
i. Choroid: blood-rich nutritive layer in the posterior of the eye
- Modified anteriorly into two structures
1. Ciliary: smooth muscle attached to lens
2. Irsi: regulates amount of light entering the eye
• Pigmented layer that gives eye color
• Pupil: rounded opening in the iris
c. Sensory inner layer
i. Retina: contains two layers:
1. Outer pigmented layer
2. Inner neural layer with photoreceptor rods and cones
3. Optic nerve: signal leave the retina toward the brain through the optic nerve
4. Optic disc: (blind spot) is where the optic nerve leaves the eyeball
- Cannot see images focused on the optic disc
ii. Rods = black and white vision
iii. Cones = color vision
1. Fovea centralis
2. Cone sensitivity
d. Lens
i. Normal function
ii. Cataracts
e. Chambers of the eye
i. Aqueous
ii. Vitreous
4. Ophthalmoscope
