Chapter 14- Eyes Flashcards
Describe the structure of the eyes as seen in front view and in horizontal section, state the principal functions of componet parts of the eye in producing a focused image of near and distant objects on retina and desicribe the pupil reflex in responsd to bright an dim light
Iris
A circular sheet of muscles. It contains a pigment which gives the eye its color. The amount of light entering the eye is controlled by the two sets of involuntary muscles in iris, circular and radial muscles
Pupil
A hole in the centre of the iris.the pipil allows light to enter the eye
Conjunctiva
A thin transparent membrane covering the sclera in the front. It is a mucous membrane, that is, it secretes mucus, thus helping to keep the front of the eyeball moist. It is continuous with the skin of the eye lids
Sclera
A tough white outer covering of the eyeball. It is continous with the cornea. It protects the eyeball from emchanical damage.
Eyelashes
They jepp to shield the eye from dust particles
Tear gland
This is a gland lyibg at the corner of the upper eylid.it secrets tears which:
•wash away dust particles
•keep the cornea moist for atmospheric oxygen to dissolve. The dissolved oxygen diffuses jnto the cornea
•lubricate the conjuctiva,hleping to reduce friction when the eyelids move
Eyelids
- they protect cornea frkm mechanicap damage
- squintjng prevents excessive light from entering eye and damgung the lught sensitive tissues inside
- Blinking spreads tears over the cornea and the conjuctiva and wipes dust particles off the cornea.
Focusing on near object
- Cilliary muscles contrct,relaxing their pull on suspensory ligaments
- SA slacken,rwlaxing their pull on lens
3 the lens, being elastic , becomes thucker and more convex, decreasing its focal length
4.light rats frkm near object are sharply focusdd on the retina. - Photoreceptors are stimulates
- Nerve impulses produced ar etramsmitted by optoc nerve to the brain. The brain interprets the impusle a nd parson sees the near kbject
Focusing on distant objext(7m or more)
- Cilliary muscles relax, pulling on suspensory ligaments
- SA become taunt,pulljng on edge of the lens
3 the lens, , becomes thinner and less convex, increasing its focal length
4.light rats frkm distant object are sharply focusdd on the retina. - Photoreceptors are stimulated
- Nerve impulses produced ar etramsmitted by optic nerve to the brain. The brain interprets the impusle a nd parson sees the distant kbject
Hoe do we se2
1.light rays r refractdd through cornea and aquoes hunour onto lens
2 lens cause further refraction and rays are brought ti a focus on retina
3.image on retina stimulate rods or cones depending on intensity of lights.
The jmage formed on the retina is upside down, laterally inverted and diminshed(smaller)
Accommodation
Or focusing
Is necessaryso that objects at different distances can be seen clearly. In focusing, the thickness or curvatyre of lens is adjustdd
Pupil reflex defination and nervous pathway
Pipil changes size as rssult if change in light ibtensity
Stimulus(change jn light intensity) Receptor(retina) SN in optic nerve BRAIN MN effector(iris)
How iris confrol amount of light entering the eye
- Cricular mucles contract
2.radkal relax
Pupil smaller
Reduvedight
VICEVERSA FOR DIM LIGHT
Cones
-Cons enable us to see colours in bright light
-there Three Types of cones red blue and green
-each contains a different pigment which absorbs light of different wavelength
-all cons work together to enable us too see a variety of colours
cons do not work in well in dim light
Rods
- Rods are more sensitive to light then cons
- Enable to see in dim light but only in black and white
- are sensitive to light of low intensity because they contain a pigment called visual purple it is bleached when bright light when the eyes exposed to bright light
- for example when you move from brightly let into dimly lit room you may not be able to see objects as it takes some time from purple to be reformed again in the rods
- formation of visual purple requires vitamin A people who definition in vitamin A unable to see in them light so they suffer from night blindness
Cilliray body
Thickened region at the front of the chorois contain cilliary muscles which control the curvature or thickness of the lens
Suspensory ligaments
Connective tissue that attaches the edge of the lens to the ciliary body
Cornea
Dome shaped transparent layer continuous with this sclera
Refracts light rays into the eye
causes most of the refraction of light
Aquous chamber
Space between the lens and cornea is filled with aquoues humour a transparent watery fluid
it keeps the front of the eyeball firm and helps to refract light Into The Pupil
Lens
Transparent circular and biconvex structure it is elastic and changes its shape or thickness in order to focus light rays on to the retina
Blind spot
Region where the optic nerve leaves the eye it does not contain any rods and cones therefore it is not light sensitive
Optic nerve
Nerve that transmits nerve impulses to brain when photoreceptors in retina stimulated
Vitreous chamber
Space behind the lens it is filled with vitreous humour a transparent Jelly like substance it keeps the eyball firm and helps to refract the light onto the retina
Choroid
The middle layer of the eyeball between the sclera and the retina it has two functions
it is pigmented block to prevent internal reflection
it contains blood vessels that bring Oxygen and nutrients to the eyeball and remove metabolic waste products
Fovea or yellow spot
. Small depression in the retina
. it is situated directly behind the lens
. this is where images are normally focused
. contains the greatest concentration of cones but not rods
. enables a person to have detailed color vision in bright light
Retina
. Innermost layer of the eyeball
. it is the light-sensitive layer on which images are formed
. contains light-sensitive cells are photoreceptors which consists of rods and cones
. cons enable to see color in bright light
. rods see in black and white and dim light
. photoreceptors are connected to nerve endings from the optic nerve
