Human Eye Flashcards
(50 cards)
How is the eye held in position?
By SIX EXTERNAL MUSCLES, that control the movement of the eye.
What cushions and protects the eye?
Fatty tissue
What is the function of the lachrymal gland?
Produces salty tears and washes away dust
What is the function of the tear duct?
Drains excess fluid into nasal cavity.
What is the function of the eyelashes and eyelids?
Protect eye from dust, too much light and foreign bodies
What is the function of the glands of Meiboom?
Secrete oily fluid to lubricate eyeball.
What is the structure and function of conjunctiva?
S: delicate mucous membrane, covers front of the eye and lines the eyelids
F: 1. Pain receptors for eyelids to close prevent foreign bodies enter.
2. Produce lubricating mucous, prevent eye drying out
What is the structure and function of Sclera?
S: tough, white in elastic layer made up of connective tissue.
F: protects internal parts of eye.
Provide points of attachment for six muscles
Inelasticity maintain shape of eye.
What is the structure and function of Cornea?
S: more convex than rest of eyeball
Transparent, has no blood vessels
Covered by conjunctiva (thin membrane)
F: transparency allow light rays pass through to light cells
Causes converging refraction of light rays
Many pain receptors, so eyelid close.
What are the three components of the Middle Vascular layer?
Choroid
Ciliary body
Iris
What is the structure and function of Choroid?
S: thin, dark layer containing pigments and blood vessels
F: pigment absorbs excessive rays of lights, preventing reflection - blurring.
Blood vessels supply food and O2 to cells of retina
What is the Structure and function of Ciliary body?
S: thickened part, extension of choroid, contains circular ciliary muscles
F: control curvature of lens
What is the structure and function of the Iris?
S:continuation of cHoroid, forms a circular coloured curtain with a hole in centre
Circular structure contains brown pigments
Two sets of involuntary muscles occur in the iris- circular and radial - when one contracts, other relaxes
Pupil is circular opening (not a struc) appears black of dark cavity.
F: controls the amount of light entering the eye. By PUPILLARY MECHANISM- reflex action
In BRIGHT LIGHT:
circular iris muscle contracts
Radial iris muscle relax
Size of pupil reduces (constricts)
Less light enters the eye. Prevent damage to retina
In DIM light:
Radial muscles contract
Circular muscle relax
Pupil dilates
Allow max amount. Of light to enter eye for clearest vision
What does the Retina consist of?
Pigmented layer 2. Nervous layer A) photoreceptors Rod cells Cone cells B) neutral layer Blind spot Yellow spot
What is the structure and functions of pigmented layer?
S:layer of cuboidal cells, borders on the choroid
F: dark pigment absorbs light
What is the structure of the nervous layer- photororecptors?
S: 2 types of photoreceptors - Rods and cones
Modified neutrons
Both sensitive to light.
F: convert light stimuli into nerve impulses.
What is the structure and function of rod cells?
S: thin, elongated cells
Found in peripheral regions of retina
F: respond to low-intensity light and provide night( black and white.)
Provide peripheral vision.
What is the structure and function of cone cells?
S: found in yellow spot of retina
Red, blue, green cones respond to diff wavelengths of light
F: respond to bright light intensities, enable colour to be seen.
Provide sharp, clear vision.
What is the structure and function of neural layer?
S: photoreceptors synapse with 2 layers of neutrons
axons of 2nd layer form optic nerve, leave the eye.
F: neutrons carry impulses from photoreceptors?
Optic nerve conduct impulses to occipital lobe of cerebral cortex, where interpreted as sight.
What is the structure and function of blind spot?
S: No rods or cones where optic nerves leave eyeball
Where blood vessels enter and leave.
F: not sensitive to light stimuli
What is the structure and function of yellow spot?
S: Near centre of retina,side of blind spot. An oval area
Contain mainly cones
F: where vision is sharpest.
What are the inner parts of the eye?
- Lens
2. Eye cavities - anterior cavity, posterior cavity
What is the structure and function of the lens?
S: round,biconvex,flexible, transparent struc,me closed in elastic
capsule.
Held in place by suspensory ligament
No blood vessels.
F: change shape to allow sharp, precise focusing of light rays on retina
What is the structure and function of anterior cavity?
S: filled with water fluid, aqueous humour.
Aqueous humour:
F: provides nutrients and O2 to lens& cornea and carries away waste.
Provides correct pressure in anterior cavity.
