chapter 14 animal receptor organs
TRANSCRIPT
Chapter 14Chapter 14
The Human Eye
Objectives• Students should be able to:
– State the relationship between receptors, the central nervous system and the effectors
– Describe the gross structure of the eye as seen in front view and in horizontal section
– State the principal functions of component parts of the eye in producing a focussed image of near and distant objects on the retina
– Describe the pupil reflex in response to bright and dim light
Sense organs
• Sense organs are receptors that receive stimuli from the environment and inform your body of any changes in the environment
14.2 The Human Eye
Upper eyelid
pupil
cornea Lower eyelid
iris
Conjunctiva (covers sclera)
Tear gland
eyelashes
Cornea• Transparent layer continuous with sclera
(white portion of the eye)• Specialised form of conjunctiva• Refracts or bend light rays into the eye
Conjunctiva• Transparent membrane• Secretes mucus, thus helping to keep
the front of the eyeball moist
Iris
• A circular sheet of muscles
• Controls the amount of light entering the eye
Pupil
• A hole in the centre of the iris
• Allows light to enter the eye
Eyelids• Protect the cornea from mechanical damage
Eyelashes• Help to shield the eye from dust particles
Tear gland• Secretes tears to wash away dust particles• Secretes tears to keep the cornea moist for
atmospheric oxygen to dissolve• Secretes tears to lubricate conjunctiva,
helping to reduce friction when the eyelids move
Chapter 14 The Human EyeStructure and Function of the Eye (Concept Map)April 11, 2023
Vertical Section of The Human Eye
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Attaches lens to ciliary body
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suspensory ligament
Vertical Section of The Human Eye
Controls amount of light enteringthe eye
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iris
suspensory ligament
Vertical Section of The Human Eye
Refracts light rays;keeps eyeball firm
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aqueoushumour
iris
suspensory ligament
Vertical Section of The Human Eye
Allows light to enter the eye
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pupil
aqueoushumour
iris
suspensory ligament
Vertical Section of The Human Eye
Refracts light rays into pupil
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cornea
pupil
aqueoushumour
iris
suspensory ligament
Vertical Section of The Human Eye
lens
Focuses light rays onto retina
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cornea
pupil
aqueoushumour
iris
suspensory ligament
Vertical Section of The Human Eye
ciliary body
Contains ciliary muscles which control curvature or thickness of the lens
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lens
cornea
pupil
aqueoushumour
iris
suspensory ligament
Vertical Section of The Human Eye
viteroushumour
Refracts light rays;keeps eyeball firm
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ciliary body
lens
cornea
pupil
aqueoushumour
iris
suspensory ligament
Vertical Section of The Human Eye
Controls movement of eyeball
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viteroushumour
ciliary body
lens
cornea
pupil
aqueoushumour
iris
suspensory ligament
rectusmuscles
Vertical Section of The Human Eye
Protects against mechanical injury
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viteroushumour
ciliary body
lens
cornea
pupil
aqueoushumour
iris
suspensory ligament
sclera
rectusmuscles
Vertical Section of The Human Eye
Pigmented black toprevent internal reflection of light; blood vessels bring oxygen and nutrients to the eyeball
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viteroushumour
ciliary body
lens
cornea
pupil
aqueoushumour
iris
suspensory ligament
choroid
sclera
rectusmuscles
Vertical Section of The Human Eye
Region where images are sharply focused
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viteroushumour
ciliary body
lens
cornea
pupil
aqueoushumour
iris
suspensory ligament
fovea(yellow spot)
choroid
sclera
rectusmuscles
Vertical Section of The Human Eye
Transmit nerve impulsesfrom eye to brain
optic nerve
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fovea(yellow spot)
choroid
sclera
rectusmuscles
viteroushumour
ciliary body
lens
cornea
pupil
aqueoushumour
iris
suspensory ligament
Vertical Section of The Human Eye
Region over optic nerve; no photoreceptors, so insensitive to light
blind spot
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viteroushumour
ciliary body
lens
cornea
pupil
aqueoushumour
iris
suspensory ligament
optic nerve
fovea(yellow spot)
choroid
sclera
rectusmuscles
Vertical Section of The Human Eye
Light-sensitive layer containingcones responsible for colour vision in bright light and rods responsible for vision in dim light
retina
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viteroushumour
ciliary body
lens
cornea
pupil
aqueoushumour
iris
suspensory ligament
blind spot
optic nerve
fovea(yellow spot)
choroid
sclera
rectusmuscles
Vertical Section of The Human Eye
Controlling the entry of light into the eye
• The pupil of the eye controls the amount of light that enters the eye
• Size of the eye is controlled by 2 sets of involuntary muscles in the iris– One set arranged radially– One set arranged in a circle around the
pupil
Chapter 14 The Human EyeAction of Iris in Bright LightApril 11, 2023
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Action of Iris in Bright Light
Circular muscles of the iris contract1
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Radial muscles of the iris relax
Action of Iris in Bright Light
2
Circular muscles of the iris contract1
Action of Iris in Bright Light
Pupil constricts and this reduces the amount of light entering the eye
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Radial muscles of the iris relax2
Circular muscles of the iris contract1
3
Chapter 14 The Human EyeAction of Iris in Dim LightApril 11, 2023
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Radial muscles of iris will contract
Action of Iris in Dim Light
Radial muscles of the iris contract1
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Action of Iris in Dim Light
Radial muscles of the iris contract1
Circular muscles of the iris relax2
Pupil dilates and this increases the amount of light entering the eye
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Action of Iris in Dim Light
Radial muscles of the iris contract1
Circular muscles of the iris relax2
3
• High light intensity, Circular muscles contract, radial muscles relax
• Pupil becomes smaller
• Low light intensity, Circular muscles relax, radial muscles contract
• Pupil becomes bigger
What is the pupil reflex?
• It is a reflex action (recall ‘Nervous System)
• Pupil changes in size as a result of changes in light intensity
• Pupil usually becomes larger when the surrounding light intensity is low, and smaller when the light intensity is high
Stimulus (change in light intensity)
Receptor (retina)
Sensory neurone in optic nerve
Brain
Motor neurone
Effector (iris)
14.3 How do we see?
• Light falling on object is reflected. Reflected rays fall on the eye.
• These rays are refracted through the cornea and the aqueous humour (watery fluid) onto the lens.
• The lens causes further refraction and the rays converge to a focus on the retina
Continue….• The image on the retina stimulates
either the rods or the cones depending on the intensity of the light.
• Image formed can be:– Upside down (inverted)– Back to front (reversed)– Smaller in size than the object being
observed (diminished)
Continue….• Impulses produced by light falling on the
rods and cones are transmitted via the optic nerve to the rear of the cerebrum.
• The brain interprets these impulses
Chapter 14 The Human EyeHow Do We See?April 11, 2023
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1
How Do We See?
objectcornea
lens
aqueoushumour
Light rays are refracted through the cornea and the aqueous humour onto the lens
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1
2
How Do We See?
objectcornea
lens
aqueoushumour
The lens causes further refraction
Light rays are refracted through the cornea and the aqueous humour onto the lens
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1
2
3
How Do We See?
objectcornea
lens
aqueoushumour
retina
Rays converge to focus on retina
The lens causes further refraction
Light rays are refracted through the cornea and the aqueous humour onto the lens
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1
2
3
4
How Do We See?
objectcornea
lens
aqueoushumour
retina
image
The image on the retina stimulates either the rods or the cones, depending on the intensity of the light
Rays converge to focus on retina
The lens causes further refraction
Light rays are refracted through the cornea and the aqueous humour onto the lens
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1
2
3
4
How Do We See?
objectcornea
lens
aqueoushumour
retina
image
The image formed is • inverted• laterally inverted• diminished in size
The image on the retina stimulates either the rods or the cones, depending on the intensity of the light
Rays converge to focus on retina
The lens causes further refraction
Light rays are refracted through the cornea and the aqueous humour onto the lens
Focusing (Accommodation)• This is the adjustment of the lens of the
eye so that clear images of objects at different distances are formed on the retina
Chapter 14 The Human EyeHow Eyes Focus on Distant ObjectsApril 11, 2023
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Parallel light rays from distant object enters eyes
Vertical section of the eye
1
How Eyes Focus on Distant Objects
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Ciliary muscles relax
Vertical section of the eye Enlarged portion of eye(front view)
1
2 2
How Eyes Focus on Distant Objects
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Suspensory ligaments become taut
Vertical section of the eye Enlarged portion of eye(front view)
1
2 2
3 3
How Eyes Focus on Distant Objects
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Lens becomes thinner
Vertical section of the eye Enlarged portion of eye(front view)
1
2 2
3 34
4
How Eyes Focus on Distant Objects
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Focal length increasesVertical section of the eye Enlarged portion of eye
(front view)
1
2 2
3 34
5
4
How Eyes Focus on Distant Objects
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Vertical section of the eye Enlarged portion of eye(front view)
Light rays from distant object focused on retina
1
2 2
3 34
5
64
How Eyes Focus on Distant Objects
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Vertical section of the eye Enlarged portion of eye(front view)
Photoreceptors stimulated
7
1
2 2
3 34
5
64
How Eyes Focus on Distant Objects
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Vertical section of the eye Enlarged portion of eye(front view)
Photoreceptors stimulated
Nerve impulses produced by optic nerves
78
1
2 2
3 34
5
64
How Eyes Focus on Distant Objects
Vertical section of the eye Enlarged portion of eye(front view)
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Photoreceptors stimulated
Transmission of nerves to brain
Nerve impulses produced by optic nerves
789
1
2 2
3 34
5
64
How Eyes Focus on Distant Objects
Vertical section of the eye Enlarged portion of eye(front view)
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Photoreceptors stimulated
Transmission of nerves to brain
Brain interprets impulses
Nerve impulses produced by optic nerves
789
10
1
2 2
3 34
5
64
How Eyes Focus on Distant Objects
Photoreceptors stimulated
Transmission of nerves to brain
Vertical section of the eye Enlarged portion of eye(front view)
Brain interprets impulses
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Person sees the distant object
Nerve impulses produced by optic nerves
789
10
111
2 2
3 34
5
64
How Eyes Focus on Distant Objects
• Far object, circular muscles of the ciliary body relax• Suspensory ligaments are pulled tight, causing the lens to become
flatter and less convex• Image sharply focused onto retina
Chapter 14 The Human EyeHow Eyes Focus on Near Objects
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Vertical section of the eye
Diverging light rays from near object enters eyes
1
How Eyes Focus on Near Objects
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Vertical section of the eye Enlarged portion of eye(front view)
Ciliary muscles contract
22
1
How Eyes Focus on Near Objects
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Vertical section of the eye Enlarged portion of eye(front view)
Suspensory ligaments become slacken
3
22
3
1
How Eyes Focus on Near Objects
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Vertical section of the eye Enlarged portion of eye(front view)
Lens becomes thicker
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3
22
3
41 4
How Eyes Focus on Near Objects
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Vertical section of the eye Enlarged portion of eye(front view)
Focal length decreases
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3
22
3
4
5
1 4
How Eyes Focus on Near Objects
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Vertical section of the eye Enlarged portion of eye(front view)
Light rays from near object focused on retina
3
22
3
4
5
61 4
How Eyes Focus on Near Objects
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Vertical section of the eye Enlarged portion of eye(front view)
Photoreceptors stimulated
3
22
3
4
5
61
7
4
How Eyes Focus on Near Objects
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Vertical section of the eye Enlarged portion of eye(front view)
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Photoreceptors stimulated
Nerve impulses produced by optic nerves
3
22
3
4
5
61
78
4
How Eyes Focus on Near Objects
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Vertical section of the eye Enlarged portion of eye(front view)
Photoreceptors stimulated
Nerve impulses produced by optic nerves
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Transmission of nerves to brain
3
22
3
4
5
61
78
9
4
How Eyes Focus on Near Objects
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Vertical section of the eye Enlarged portion of eye(front view)
Photoreceptors stimulated
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Nerve impulses produced by optic nerves
Transmission of nerves to brain
Brain interprets impulses
3
22
3
4
5
61
78
9
10
4
How Eyes Focus on Near Objects
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Vertical section of the eye Enlarged portion of eye(front view)
Photoreceptors stimulated
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Nerve impulses produced by optic nerves
Transmission of nerves to brain
Brain interprets impulses
Person sees the near object
3
22
3
46
1
5
78
9
10
11
How Eyes Focus on Near Objects
4
• Near object, circular muscles of the ciliary body contracts• Suspensory ligaments releases the pull on the lens• Elastic nature of the lens causes it to become thicker and more convex• Image focused sharply on the retina• After a certain distant called near point, the lens cannot adjust anymore.
The image formed will then be blur
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Vertical Section of The Human Eye
Pupil Reflex
A reflex action in which the pupil changes size as a result of changes in light intensity.
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Vertical Section of The Human Eye
Pupil Reflex
In bright light
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In bright light• Circular muscles in iris contract.• Radial muscles relax.• Pupil becomes smaller, hence less light enters the eye
Vertical Section of The Human Eye
Pupil Reflex
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Vertical Section of The Human Eye
Pupil Reflex
In bright light• Circular muscles in iris contract.• Radial muscles relax.• Pupil becomes smaller, hence less light enters the eye
In dim light
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In dim light• Radial muscles in iris contract .• Circular muscles in iris relax.• Pupil enlarges, hence more light enters the eye
Vertical Section of The Human Eye
Pupil Reflex
In bright light• Circular muscles in iris contract.• Radial muscles relax.• Pupil becomes smaller, hence less light enters the eye
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Vertical Section of The Human Eye
Pupil Reflex Focusing
In bright light• Circular muscles in iris contract.• Radial muscles relax.• Pupil becomes smaller, hence less light enters the eye
The adjustment of the lens of the eye so that clear images of objects at different distances are formed on the retina.
In dim light• Radial muscles in iris contract .• Circular muscles in iris relax.• Pupil enlarges, hence more light enters the eye
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Vertical Section of The Human Eye
Pupil Reflex Focusing
In bright light• Circular muscles in iris contract.• Radial muscles relax.• Pupil becomes smaller, hence less light enters the eye
Distant object (7 metres or more)
In dim light• Radial muscles in iris contract .• Circular muscles in iris relax.• Pupil enlarges, hence more light enters the eye
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Vertical Section of The Human Eye
Pupil Reflex Focusing
In bright light• Circular muscles in iris contract.• Radial muscles relax.• Pupil becomes smaller, hence less light enters the eye
Distant object (7 metres or more)
• Ciliary muscles relax• Suspensory ligament become taut• Lens becomes thinner and less convex
In dim light• Radial muscles in iris contract .• Circular muscles in iris relax.• Pupil enlarges, hence more light enters the eye
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Vertical Section of The Human Eye
Pupil Reflex Focusing
In bright light• Circular muscles in iris contract.• Radial muscles relax.• Pupil becomes smaller, hence less light enters the eye
Distant object (7 metres or more)
• Ciliary muscles relax• Suspensory ligament become taut• Lens becomes thinner and less convex
Near objectIn dim light• Radial muscles in iris contract .• Circular muscles in iris relax.• Pupil enlarges, hence more light enters the eye
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Distant object (7 metres or more)
• Ciliary muscles relax• Suspensory ligament become taut• Lens becomes thinner and less convex
Near object• Ciliary muscles contract• Suspensory ligaments slacken• Lens becomes thicker and more convex
Vertical Section of The Human Eye
Pupil Reflex Focusing
In bright light• Circular muscles in iris contract.• Radial muscles relax.• Pupil becomes smaller, hence less light enters the eye
In dim light• Radial muscles in iris contract .• Circular muscles in iris relax.• Pupil enlarges, hence more light enters the eye