Transcript Eye - KingsfieldBiology

SENSORY RECEPTORS.
SENSORY RECEPTORS.
Objectives:
E - label the parts of the eye
D – Describe their functions
C – explain how parts function to adjust
focus and the amount of light entering the
eye
The eye as a receptor
vitreous
humour
choroid
choroid
iris
retina
cornea
pupil
aqueous
humour
ciliary
body
lens
optic
nerve
Soper 2 p593
• Draw eye diagram and label functions
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Iris
Cornea
Sclera
Choroid
Ciliary muscles
Conjunctiva
Adjustment
Longitudinal
muscles
• Radial muscles
• Suspensory
ligaments
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Lens
Pupil
Eyelid
Aqueous humour
Vitreous humour
Retina
Fovea
Optic nerve
Dilation
Constriction
• Far object
• Close object
Accomodation
• This is the focusing of light by the lens
Dilation & constriction
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Iris
Cornea
Sclera
Choroid
Ciliary muscles
Conjunctiva
Rhodopsin
Longitudinal
muscles
• Radial muscles
• Suspensory
ligaments
• cones
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Lens
Pupil
Eyelid
Aqueous humour
Vitreous humour
Retina
Fovea
Optic nerve
Visual accuity
Constriction
• Far object
• Close object
• Rods
The retina
Blood vessel
in choroid
optic nerve
fibres
nuclei of
ganglion cells
nuclei of bipolar
cells
synapses
nuclei of retinal
cells
retinal rod and
cone cells
choroid
LIGHT
Inner segments of
rod and cone cells
cell bodies of rod and
cone cells
rod cell
cone cell
optic nerve
fibres
ganglion cell
bipolar cell
cell body
rod cell
synapse
cone cell
Structure of the retina
Photoreceptor
cells
(Rods and cones)
Bipolar neurones
connect photoreceptors to optic
nerve
•rods connected in groups
•cones connected singly
Axons of ganglion cells
• optic nerve
• visual area of the brain
Melanin – absorbs
light to prevent
internal reflection
fovea
Approx 1mm diameter on visual axis of eye
Cones only
Point of maximum intensity of vision
Main point of interest in visual field focused
here
fovea
blind
spot
All axons of ganlion cells converge here to
form the optic nerve
No photoreceptors so not capable of
forming an image
Rhodopsin located in membrane of discs
Photosensitive pigment
Rod cell is a modified bipolar neurone
How cone cells work; colour vision
• Cone cells work in basically the same
way as rod cells.
• However bleaching requires a much
higher light intensity (so cone cells
cannot function in dim light).
There are three different
types of rhodopsin (the
opsin protein part differs),
which have maximum
absorption at different
wavelengths so cones cells
allow for the discrimination
of colour; there are
•blue-absorbing cones (max
absorption at 445nm)
•green-absorbing cones
(max absorption at 535
nm)
•red-absorbing cones
(max absorption at 570
nm)
• this is the trichromatic theory of colour
vision
• different colours are perceived as a result of
the degree of stimulation of the blue + green
+ red cones (i.e. colours are the result of the
mixture of inputs from all three cone types)
• By population, about 64% of the cones are
red-sensitive, about 32% green sensitive, and
about 2% are blue sensitive
for example: % refers to the light
absorbed as a % of the maximum*
0% blue + 83% green + 83% red
 yellow
31% blue + 67% green + 26% red
 green
•*hence the size of the generator potentials produced, which in turn
determines the number of nerve impulses from each type of cone cell,
which is then interpreted by the brain as a particular colour