Special Senses Chapter 8

Special senses ▫Smell ▫Taste ▫Sight ▫Hearing ▫Equilibrium

The Eye and Vision 70% of all sensory receptors are in the eyes Each eye has over a million nerve fibers

The Eye and Vision How are the delicate eyes protected?

Accessory Structures of the Eye Eyelids and eyelashes Conjunctiva Lacrimal apparatus Extrinsic (external) eye muscles

Eyelids and eyelashes Tarsal glands lubricate the eye

Eyelids and eyelashes Ciliary glands are located between the eyelashes

Conjunctiva Membrane that lines the eyelids Connects to the surface of the eye Secretes mucus to lubricate the eye ▫Not white, just membrane covering it ▫ENDS AT THE CORNEA!

Lacrimal Apparatus Lacrimal gland—produces lacrimal fluid Lacrimal canals—drain lacrimal fluid from eyes Lacrimal sac—passage of lacrimal fluid towards nasal cavity Nasolacrimal duct—empties lacrimal fluid into the nasal cavity

Lacrimal Apparatus

Lacrimal Fluid Dilute salt solution (tears) Contains antibodies and lysozyme

Internal Anatomy of the Eye Sclera ▫White connective tissue layer ▫“white of the eye”

Cornea ▫Transparent – light passes through ▫Repairs itself easily ▫Curved structure

Internal Anatomy of the Eye Iris ▫Colored part of eye ▫Regulates amount of light entering eye ▫Muscle

Pupil ▫Simply a hole in the iris

Internal Anatomy of the Eye In bright light, the iris expands and the pupil gets smaller In low light, the iris contracts and the pupil gets bigger

Aqueous Humor ▫Clear liquid between corner and iris Internal Anatomy of the Eye

Lens (behind iris) ▫Changes shape to focus light ▫Convex shape

Internal Anatomy of the Eye Ciliary body ▫Smooth muscle attached to lens ▫Control shape of lens

Vitreous Humor ▫Clear gel-like substance behind lens ▫Prevents collapse of eyeball Internal Anatomy of the Eye

Retina (2 layered) ▫Inner layer transparent  Millions of receptor cells ▫Outer layer pigmented (black)  Absorb light  Prevent light from scattering

Internal Anatomy of the Eye Choroid ▫Most posterior layer ▫Blood/nutrient rich ▫Dark pigment ▫Anteriorly choroid is modified to form iris and ciliary body (muscles)

Internal Anatomy of the Eye Optic nerve Optic disc (blind spot) Fovea Centralis