chapter 8 notes

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: A bony orbit

2.    Accessory structures – not directly involved with actual vision

a.    Eyelids and eyelashes: Prevent particles from going into the eye.

                                          i.    Tarsal (oil) glands-Lubricate the eye

                                        ii.    Ciliary (sweat) glands- Located between the eyelashes

b.    Conjunctiva: Membrane lines the eyelids

                                          i.    Connects – to the surface of the eye

                                        ii.    Secretes- Mucus, lubricates eye

c.    Lacrimal = tear apparatus

                                          i.    Gland- produces fluid

                                        ii.    Canals- drain fluid from eyes

                                       iii.    Sac-passage of fluid towards nasal cavity

                                       iv.    Nasolacrimal apparatus- empties fluid into the nasal cavity

                                         v.    Functions-protects, moistens, and lubricates the eye

                                       vi.    Properties- dilute salt solution (tears), contains anitobodies and lysozyme (antibacterial), possibly contain hormones (anti-aggressive)

d.    Extrinsic eye muscles-six muscles attach to the outer surface of the eye

3.    Layers forming wall of eyeball:

a.    Fibrous outside layer

                                          i.    Sclera- “white of the eye”, connective tissue

                                        ii.    Cornea- Transparent, central anterior portion, allow for light to pass through, repairs itself easily, the only human tissue that can be transplanted without fear of dissection.

b.    Vascular middle layer

                                          i.    Choroid- blood-rich nutritive layer in the posterior of the eye, modified anteriorly into two structures

                                        ii.    Ciliary- smooth muscle attached to lens

                                       iii.    Iris – regulates amount of light entering eye: pigmented layer that gives eye color, pupil= rounded opening in the iris.

c.    Sensory inner layer

                                          i.    Retina

1.     Outer- pigmented layer

2.    Inner – neutral layer with photoreceptor rods and cones

3.    Optic nerve- signals 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