The Eye

Question 1

Conjunctiva

Answer 1

Thin membrane lining inside of eyelids - covering sclera

Lubricates and protects tissues at front of eye

Prevents foreign bodies entering eye orbit

Question 2

Sclera

Answer 2

Tough white outer layer that encloses eye

Protects eyeball against mechanical damage

Allows attachment of eye muscles

Question 3

Cornea

Answer 3

Transparent front part of eye - continuous with sclera

Allows passage of light while refracting it

Question 4

Iris

Answer 4

Coloured part of eye - contains circular and radial muscles

Controls size of pupil to adjust amount of light entering eye

Question 5

Pupil

Answer 5

Gap within iris - appears black

Allows light to enter eye and not leave

Size can be varied

Question 6

Aqueous Humour

Answer 6

Transparent watery fluid filling the front part of the eye

Maintains shape of the front chamber of the eye

Question 7

Lens

Answer 7

Transparent and elastic ovoid structure held in place behind cornea

Changes shape of adjust focusing of light onto retina

Question 8

Ciliary Body

Answer 8

Structure which supports the lens and contains circular muscle

Contraction or relaxation of circular muscle controls shape of lens

Question 9

Suspensory Ligaments

Answer 9

Strong ligaments which contact ciliary body to lens

Transfers tension in wall of eyeball to lens to make the lens thinner

Question 10

Vitreous Humour

Answer 10

Transparent, jelly like material filling the rear part of the eyeball

Maintains shape of rear part of eyeball and supports lens

Question 11

Retina

Answer 11

Inner layer of wall of eyeball containing light-sensitive cells

Rods and cones initiate impulses in associated neurones when appropriately stimulated

Question 12

Fovea

Answer 12

Region in back of retina that is rich in cones

A region with high visual acuity that allows coloured vision

Question 13

Choroid

Answer 13

Layer pigmented cells at back of eyeball, behind retina

Contains blood vessels which supply retina

Prevents reflection of light within the eyeball

Question 14

Optic Nerve

Answer 14

Bundle of sensory nerve fibres which leaves from back of eye

Transmits impulses from retina to optic centre at back of brain

Question 15

Blind Spot

Answer 15

Region where optic nerve leaves inside eyeball - no light sensitive cells

Region which, if light strikes it, is not sensitive to light

Question 16

Iris in Bright Light

Answer 16

Circular Muscles contract
Radial Muscles relax
Iris Dilates
Pupil Constricted - limit amt light passing

Question 17

Why is pupil restricted in bright light

Answer 17

It can damage rods and cones initiate impulses

Question 18

Iris in Dim Light

Answer 18

Circular Muscles Relax
Radial Muscles Contract
Pupil Dilates - allow more light for maximal stimulation cells

Question 19

Accommodation

Answer 19

Ability to adjust focusing

Question 20

Near Object Accomodation

Answer 20

Circular muscles of ciliary body contract - closes aperture around the lens and releases any tension from the eyeball

Lens (being elastic) adopts a fatter shape - refracts light more - accom light onto retina

Question 21

Far Object Accomodation

Answer 21

Eye wall under pressure by being filled with fluid

Ciliary body relax, pressure transferred via sus ligaments to lens - pulling it into thin shape

Lens does not converge light as much

Question 22

Where are Rods and Cones mainly found

Answer 22

Cones in Fovea

Rods in periphery of retina

Question 23

Retinal Convergence

Answer 23

Rods and cones synapse w/bipolar neurones - which synapse with neurones of optic nerve

Many rods synapse with each bipolar neurone and many bipolar cells connect w/ each neurone of optic nerve

Question 24

How do cones generally Synapse

Answer 24

Generally with a single bipolar neurones and a single neurone of optic nerve

Question 25

Consequence of light passing through neurones before reaching outer segments of rods and cones

Answer 25

For neurones to leave the eye they must pass through the layer of photoreceptors Creates area devoid of receptors - **blind spot**

Question 26

Rod pigment

Answer 26

Rhodopsin Composed of protein (opsin) and light-absorbing cmpnd - retinal

Question 27

Generator Potential

Answer 27

Light strikes rhodopsin, it breaks down into retinol and opsin Results in change in membrane potential of rod cell

Question 28

What does generator potential cause

Answer 28

Change in membrane potential of neighbouring bipolar neurone. Bpn releases transmitter substance into its synapse with a neurone of the optic nerve -if sufficient AP generated and transmitted to visual centre back of brain

Question 29

Why are Rod cells light sensitive

Answer 29

•Rhodopsin absorbs light readily and is more easily broken down •Retinal convergence enables summation

Question 30

Summation

Answer 30

With low intensity stimuli, generator potentials have an additive effect in stimulating bipolar neurones

Question 31

Consequence of Retinal Convergence

Answer 31

Brain cannot distinguish which rod of a group sharing the same optic fibre has been stimulated - decreased visual acuity Rods lack ability to discriminate detail

Question 32

Dark adaption

Answer 32

Rhodopsin resynthesised with ATP from mitochondria Rate efficient to continue functioning in dim light Bright Light - rhodopsin almost entirely bleached - takes about 30min in complete darkness for all to be reformed - dark adaption

Question 33

Cones pigment

Answer 33

Iodopsin Less readily broken down Produce generator potential in bright light only

Question 34

Visual Acuity

Answer 34

Brain is able to distinguish between points that are close together

Question 35

Types of Iodopsin

Answer 35

Red Green Blue

Question 36

Theory Iodopsin

Answer 36

Trichromatic Theory Of Colour Vision Each iodopsin sensitive to diff wavelengths of light Pure red light will only break down red iodopsin in red cones fire impulses - interpreted to red Yellow light breaks down some red and some green so both red and green cones fire impulses

Question 37

Binocular vision

Answer 37

Predatory animals or primates have eyes positioned on front of head - use both eyes to view an object creating a single image Allows more accurate judgement of distance

Question 38

Stereoscopic Vision

Answer 38

Allowed by binocular vision As a result of increase in depth perception - brain can create 3D image