human eye Flashcards
function of eyelid
-protect cornea from excessive damage
-closing eye to prevent excessive light from entering
-blinking spread tears over the eyes so dust is wiped off
function of eyelashes
-shield eye from dust particles
function of tears
-washes away dust particles
-keep the cornea moist for atmospheric oxygen to dissolve
-lubricates conjunctiva, reduce friction when eyelid moves
function of cornea
-dome shaped transparent layer to bend or refract light rays into eyes
function of iris
-circular sheet of muscles that contain pigment that gives eye colour
-controlled by circular and radial involuntary muscles
function of pupil
-hole in center of eye that allows light to enter
function of conjunctiva
-mucus membrane that covers sclera,
-sclera secretes mucus to keep front of eyeball moist
what is the sclera
-tough white outer covering of the eyeball
-continuous of cornea
function of lens
-transparent circular biconvex structure that change shape and thickness to refract light into retina
function of ciliary body
-contains ciliary muscles that controls the curvature and thickness of lens
function of suspensory ligament
-ligaments that attach edge of lens to ciliary body
function of choroid
-black pigmented middle layer of eyeball that prevents internal reflection of light
-contains blood vessels to carry oxygen and nutrients to eyeball while removing carbon dioxide and waste products
what is vitreous humour and where is it found
-transparent jelly like substance that keeps eyeball firm and reflects light to retina
-in vitreous chamber, space behind lens
what is aqueous humour and where is it found
-transparent water like substance that keeps front of pupil firm and refract light into pupil
-in aqueous chamber, space between cornea and lens
function of retina
-contains photoreceptors, light sensitive cell that has rods and cones
what is fovea/yellow spot
-small yellow depression where images are not focused
-contains cones but no rods, cones are for colour vision, rods are for seeing in the dark
-more detail colour vision in bright light
function of optic nerve
-nerve that transmit nerve impulses to brain upon stimulation of photoreceptors
what is blind spot
-region where optic nerve leaves the eye
-absence of rods and con so sensitivity to light
what is the pupil reflex
-reflex action involving receptors and effectors that occurs as a result of changes in light intensity
process of pupil reflex
-stimulus, change in light intensity
-receptors within the retina
-sensory neurone in optic nerve sends nerve impulses to brain
-nerve impulses from brain to motor neurone
-to effecters, iris
how does iris control the amount of light entering our eyes
-iris controlled by two sets of involuntary radial and circular muscles that work antagonistically
-Bright light, circular muscle contract, pupil constrict, reduce amount of light entering eyes
-dim light, radial muscle contracts, pupils dilate, increase amount of light entering eyes
what is the formation of image in retina
-light rays are refracted when it passes through the cornea and aqueous humour
-light rays further refracted when it passes through the lens
-image in retina is stimulates either rods or cones depending on intensity of light
-image formed on retina usually inverted, laterally inverted and smaller than in size than real object
what is the role of brain in vision
-the image is made upside down by the retina, brain makes it upright
-brain contains corrective function
-when blind people’s sight restores, objects appear upside down to them at first before brain learns how to correct it
what is focusing and how is it done
-adjustment of lens of the eye so that clear images of objects at different distance are formed in retina
-adjustment of thickness or curvature of lens
-allows light rays to focus on retina, enabling a clear image in retina to be formed
how to focus on distant object
-ciliary body relax, pulling on suspensory ligaments
-suspensory ligaments become taunt, pulling on edge of lens
-lens become thinner and less convex, increasing focal length, distance between middle of lens to point of focus on retina
-light rays focus on retina
-photoreceptors are stimulated, nerve impulses transmitted to brain, interpreted by the brain that allows person to see object
how to focus on near object
-ciliary body contracts, relaxing pull on suspensory ligaments
-suspensory ligaments slacken, lessening pull on edge of lens
-lens become thicker and more convex, decreasing focal length
-light rays focus on retina
-photoreceptors stimulated, nerve impulses transmitted to brain, interpreted by the brain that allows person to see object
properties of rods
-more sensitive to light than cones
-enable vision in dim light in black and white
-pigment visual purple, gets bleached when exposed to bright light, nerve impulses cannot be sent to brain, hence person has no vision in bright light
-time taken for visual purple to reform in rods before we can see in the dark, hence cannot see for some time from bright lighted room to dimly lit room
-formation of visual purple required vitamin A, night blindess affect vitamin A deficiency
properties of cones
-enable us to see colours in bright light
-red blue and green cones each absorb light of different wavelengths and together enable us to see a variety of colours, do not work well in dim light
what is colour blindness
-person is not able to perceive certain colours, of the three basic cones that allow us to see the three basic colours is missing
