the human eye

Question 1

describe the human eye?

Answer 1

• each eyeball lies in a hollow in the skull called the orbit
• each eyeball is attached to the skull by rectus muscles which control eye movement

Question 2

what are the parts of the eye that can be seen?

Answer 2

• iris
• conjunctiva
• pupil
• eyelash
• upper eyelid
• lower eyelid
• sclera
• conjunctiva

Question 3

what is the function of the iris?

Answer 3

• circular sheet of muscles
• contains pigment that gives eyes colour
• has two sets of involuntary muscles, circular and radial muscles
• control the amount of light entering the eye

Question 4

what is the function of the pupil?

Answer 4

• hole in the centre of the iris

- allows light to enter eye

Question 5

what is the function of the sclera/scelrotic coat

Answer 5

• tough, white outer covering of eyeball
• continuous with cornea
• protects eyeball from machenical damage

Question 6

what is the function of the conjunctiva?

Answer 6

• thin, transparent, mucous membrane covering scelra in front of it
• secretes mucus to keep front of eyeball moist
• continuous with skin of eyelids

Question 7

what is the function of eyelashes?

Answer 7

• shield eye from dust particles

Question 8

what is the function of eyelids?

Answer 8

• protect cornea from mechanical damage
• squint to prevent excessive light from entering eye and damaging light sensitive retina
• blinking spreads tears over cornea and conjunctiva and wipes dust particles off cornea

Question 9

what is the function of tear glands?

Answer 9

• secretes tears that:
• wash away dust particles
• keep cornea moist for atmospheric oxygen to dissolve. Dissolved oxygen diffuses into cornea
• lubricates conjunctiva, helping to reduce friction when eyelids move

Question 10

name the parts of the internal eye?

Answer 10

• ciliary body
• superior rectus muscle
• choriod
• scelera
• foreal yellow spot
• blind spot
• vitreous chamber
• retina
• inferior rectus muscle
• lens
• aqueous chamber
• cornea
• iris
• suspensory ligament

Question 11

what is the function of the cornea?

Answer 11

• transparent layer, continuous with sclera
• refracts or bends light rays into eyes
• causes most refraction of light that occurs in eye

Question 12

what is the function of the aqeous chamber?

Answer 12

• space between cornea and lens
• filled with aqueous humour, a transparent water fluid
• keeps front of eyeball firm, and helps to refract light into the pupil

Question 13

what is the function of the lens?

Answer 13

• transparent, circular and biconvex structure. Elastic

- changes shape and thickness to focus light onto retina

Question 14

what is the function of the ciliary body?

Answer 14

• contains ciliary muscles

- controls curvature or thickness of lens

Question 15

what is the function of the suspensory ligament?

Answer 15

• connective tissue, attaches edge of lens to ciliary body

- transmits force from ciliary muscles to the attached lens

Question 16

what is the function of vitreous chamber?

Answer 16

• space behind lens, filled with vitreous humour, a transparent, jelly-like substances
• keeps eyeball firm and helps to refract light onto retina

Question 17

what is the function of the retina?

Answer 17

• innermost layer of eyeball
• light-sensitive, contains photoreceptors
• site whre images are formed

Question 18

what is the function of the forea/yellow spot?

Answer 18

• small depression in retina
• site where images are normally focused
• enables detailed colour vision in bright light

Question 19

what is the function of the blindspot?

Answer 19

• region where optic nerve leaves eye

- not sensitive to light

Question 20

what is the function of the choriod?

Answer 20

• middle layer of eyeball between retina and sclera
• pigmented black to prevent internal reflection of light
• contains blood vessels that bring oxygen and nutrients to eyeball and remove metabolic waste products

Question 21

what is the function of the optic nerve?

Answer 21

• transmits nerve impulses to brain when photoreceptors in retina are stimulated

Question 22

what are the photoreceptors in the retina?

Answer 22

• consists of rods and cones

- connected to nerve endings from optic nerve

Question 23

what is the function of cones?

Answer 23

• enable us to see colours in bright light
• red, green and blue cones
• each cone contains different pigments which absorbs light of differing wavelengths
• do not work well in dim light

Question 24

what is the function of rods?

Answer 24

• enable us to see in dim light, but only in black and white
• more senstivie than cones
• sensitive to dim light because they contain the pigment visual purple which is bleached in bright light
• visual purplse must be reformed to see in dim light again
• takes awhile to reform + requires vitamin A

Question 25

what is pupil reflex?

Answer 25

- reflex action - pupil changes size due to change in light intensity - eyelids may come closer to screen off part of the light if it is too bright - prevents excessive light from damaging retina

Question 26

describe the pathway of the neurones?

Answer 26

change in light intensity --> photoreceptors in retina are stimulated and generate nerve impulses --> nerve impulses transmitted along sensory neurone in optic nerve to brain --> nerve impulses transmitted across a synhapse to relay neurone in brain --> nerve impulses transmitted across another synapse to motor neurone and to effector

Question 27

how does the iris control the amount of light entering the eye in bright light?

Answer 27

- circular muscles of iris contract - the radial muscles of iris relax - pupil becomes smaller or constricts this reduces amount of light entering eye

Question 28

how does the iris control the amount of light entering the eye in dim light?

Answer 28

- circular muscles of iris relax - radial muscles of iris contract - pupil dilates. This includes the amount of light entering the eye

Question 29

how do we see?

Answer 29

1. light rays are refracted through cornea and the aqueous humour onto the lens 2. lens cause further refraction and rays are brought to a focus on the retina 3. image on retina stimulates either rod or cones, depending on light intensity - image formed on retina is: * upside down * laterally inverted * diminished - nerve impulses produce when light falls on rod/come. Transmitted via optic nerve to brain, which interpret impulses so object is seenat right size

Question 30

define focusing?

Answer 30

adjustment of lens of the eye so that clear images of objects at different distances are formed on retina

Question 31

what happens when focusing on distant object (>7m)

Answer 31

1. ciliary muscles relax, pulling on the suspensory ligament 2. suspensory ligament becomes taut, pulling on edge of lens 3. lens become thinner and less convex, increases focal length 4. light rays from distanct object are sharply focused on retina 5. photoreceptors stimulated 6. nerve impulses produce are transmitted by optic nerve to brain. Brain interprets impulses and person sees the object

Question 32

what happens when focusing on nearby object?

Answer 32

1. ciliary muscles contract, relaxing their pull on on suspensory ligaments 2. suspensory ligaments slacken, relaxing their pull on the lens 3. the lengs, being elastic, becomes thicken and more convex, decreases focal length 4. light rays from near objects are sharply focused on retina 5. photoreceptors stimulated 6. nerve impulses produced are transmitted by optic nerve to brain. Brain interprets the impulses and person sees the object