Chapter 14- Eyes

Question 1

Iris

Answer 1

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

Question 2

Pupil

Answer 2

A hole in the centre of the iris.the pipil allows light to enter the eye

Question 3

Conjunctiva

Answer 3

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

Question 4

Sclera

Answer 4

A tough white outer covering of the eyeball. It is continous with the cornea. It protects the eyeball from emchanical damage.

Question 5

Eyelashes

Answer 5

They jepp to shield the eye from dust particles

Question 6

Tear gland

Answer 6

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

Question 7

Eyelids

Answer 7

• 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.

Question 8

Focusing on near object

Answer 8

1. Cilliary muscles contrct,relaxing their pull on suspensory ligaments
2. 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.
3. Photoreceptors are stimulates
4. Nerve impulses produced ar etramsmitted by optoc nerve to the brain. The brain interprets the impusle a nd parson sees the near kbject

Question 9

Focusing on distant objext(7m or more)

Answer 9

1. Cilliary muscles relax, pulling on suspensory ligaments
2. 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.
3. Photoreceptors are stimulated
4. Nerve impulses produced ar etramsmitted by optic nerve to the brain. The brain interprets the impusle a nd parson sees the distant kbject

Question 10

Hoe do we se2

Answer 10

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)

Question 11

Accommodation

Answer 11

Or focusing
Is necessaryso that objects at different distances can be seen clearly. In focusing, the thickness or curvatyre of lens is adjustdd

Question 12

Pupil reflex defination and nervous pathway

Answer 12

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)

Question 13

How iris confrol amount of light entering the eye

Answer 13

1. Cricular mucles contract
   2.radkal relax
   Pupil smaller
   Reduvedight

VICEVERSA FOR DIM LIGHT

Question 14

Cones

Answer 14

-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

Question 15

Rods

Answer 15

• 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

Question 16

Cilliray body

Answer 16

Thickened region at the front of the chorois contain cilliary muscles which control the curvature or thickness of the lens

Question 17

Suspensory ligaments

Answer 17

Connective tissue that attaches the edge of the lens to the ciliary body

Question 18

Cornea

Answer 18

Dome shaped transparent layer continuous with this sclera
Refracts light rays into the eye
causes most of the refraction of light

Question 19

Aquous chamber

Answer 19

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

Question 20

Lens

Answer 20

Transparent circular and biconvex structure it is elastic and changes its shape or thickness in order to focus light rays on to the retina

Question 21

Blind spot

Answer 21

Region where the optic nerve leaves the eye it does not contain any rods and cones therefore it is not light sensitive

Question 22

Optic nerve

Answer 22

Nerve that transmits nerve impulses to brain when photoreceptors in retina stimulated

Question 23

Vitreous chamber

Answer 23

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

Question 24

Choroid

Answer 24

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

Question 25

Fovea or yellow spot

Answer 25

. 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

Question 26

Retina

Answer 26

. 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