Chapter 8 Senses

Chapter 8 Special Senses
Part A: Vision
1. The eye and vision
a. 70% of all sensory receptors
b. Each eye – over a million nerve fibers
c. Protection for the eye:
i. A bony orbit
ii. A surrounding cushion of fat
2. Accessory structures – not directly involved with actual vision
a. Eyelids and eyelashes: prevent some particles from going in the eye
i. Tarsal (oil) glands lubricate the eye
ii. Ciliary (sweat) glands located between the eyelashes
b. Conjunctiva: membrane lines the eyelids
i. Conjunctivitis (pink eye)
ii. Connects to the surface of the eye
iii. Secretes mucus, lubricates eye
c. Lacrimal = tear apparatus
i. Gland- produces fluid
ii. Canals- drain fluid from the eyes
iii. Sac- passage of fluid towards nasal cavity
iv. Nasolacrimal duct- empties fluid into the nasal cavity
v. Functions- protects, moistens, and lubricates the eye, empties into the nasal cavity
vi. Properties of lacrimal fluid- dilute salt solution (tears)
vii. Contains antibodies and lysozyme (antibacterial)
viii. Possible contain hormones (anti-aggressive)
d. Extrinsic eye muscles:
i. Six muscles attach to the outer surface of the eye
ii. Produce eye movements
3. Layers forming wall of eyeball:
a. Fibrous (outside layer)
i. Sclera- “white of the eye” connective tissue (collagen)
ii. Cornea-
1. transparent, central anterior portion
2. Repairs itself easily
3. The only human tissue that can be transplanted without fear of rejection (done with cataracts or when light cannot pass through)
b. Vascular (middle layer)
i. Choroid- blood rich nutritive layer in the posterior of the eye
1. Modified anteriorly into two structure
ii. Ciliary body- smooth muscle attached to lens
iii. Iris- regulates amount of light entering eye:
1. Pigmented layer that gives eye color
2. 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- signals leave the retina toward the brain
4. Optic disc (blind spot)- where the optic nerve leaves the eyeball
a. 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