special senses

eyelids

aka palpebrae

-shades eyes during sleep and protects them from excessive lights

-spread lubricating secretions over eyes (tears)

eyebrows

protects from foreign objects, perspiration (sweating), shade eyes from sun

palpebral fissure

opening for eye

canthus (commissure)

where 2 palpabrae meet

caruncle

modified oil/sweat glands, producing whitish material that collects (e.g. at night)

conjunctiva

mucous membrane that forms inner lining of eyelid

-attaches at palpebral fissure

-lines eyelid and folds back on itself to cover white of eye

-can respond to irritants (which can cause inflammation to conjunctiva “conjunctivitis”)

two types of conjunctiva

bulbar conjunctiva (lining for white of the eye)

palpebral conjunctiva (lining the eyelid)

describe the flow of tears

lacrimal glands secrete tears into lacrimal ducts (on superior lateral side) → ducts distribute tears over surface of eyeball → tears move medially and inferiorly towards medial commissure; excess tears collect on medial corner of eye and enter the puncta → move into superior/inferior lacrimal canaliculi → tears drained into lacrimal sac → tears drained into nasolacrimal duct → drains tears nasal cavity

describe retina behaviour for distant vision

-ciliary muscles in ciliary body are relaxed

-tension in suspensory ligaments is high

-lens flattened

-rays are parallel from distant object

describe retina behaviour for near vision

-ciliary muscle in ciliary body contract, moving ciliary body toward lens and decrease ciliary rings

-tension in suspensory ligaments is low

-lens thickened

divergent rays from close object