Summary
Summary of the human eye and ear. Functions, locations, etc.
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- Life Sciences
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- 11
This document is a summary of the human eye and ear. It includes the structure, functions and defects of the eye and ear.
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RECEPTORS pg168-180 Detect changes (stimuli) in environment by means of receptors.
From receptors, impulses are conducted along sensory neurons to CNS to be interpreted.
Travel along motor neurons to bring correct response.
General receptors: mostly modified dendrites of sensory neurons and are distributed throughout
body.
Special sensory receptors: receptor cells found in the head region. May be:
1. Complex sensory organs: eyes and ear
2. Epithelial structures: taste buds, olfactory epithelium
HUMAN EYE
Where
Bony socket situated anteriorly in the cranium.
Held by 6 external muscles which control movements.
Posteriorly fatty tissue cushions it.
External features
Eyelids and eyelashes: protect eye from dust, too much light, foreign bodies.
Glands of Meiboom: secrete oily fluid to lubricate the eyeball.
Lachrymal gland: produces salty tears, washes away dust, keeps conjunctiva moist.
Tear flow
Tear duct drains: excess fluid into nasal cavity.
Internal structure
1. Ciliary
2. Ciliary body
3. Suspensory ligament
4. Anterior cavity with aqueous humor
5. Lens
6. Pupil
7. Cornea
8. Iris
9. Conjunctiva
10. Posterior cavity with vitreous humor
11. Sclera
12. Choroid
13. Retina
14. Yellow spot with central fovea
15. Blind spot
16. Optic nerve
, Conjunctiva
Structure:
Delicate mucous membrane that covers the front of the eye and lines the eyelid.
Functions:
1. Has pain receptors that reflexively cause the eyelids to close preventing foreign bodies from
entering.
2. Produces lubricating mucus that prevents the eyelids from drying out.
Sclera
Structure:
Tough, white inelastic layer is made up of connective tissue and covers the posterior 5/6 of the
eyeball.
Functions:
1. Protects the internal parts of the eye.
2. Provides points of attachment for the six extrinsic eye muscles.
3. Inelastic nature helps to maintain the eye shape.
Cornea
Structure:
Continuation of sclera.
More convex (bulgy)
Transparent
Covered by conjunctiva
Functions:
1. Being transparent, allows light rays to pass through to light-sensitive cells.
2. Causes converging refraction of light rays. Greatest refraction here.
3. Conjunctiva has many pain receptors which enable eyelids to close reflexively when foreign matter
touches surface of the eye.
Choroid
Structure:
Thin, dark layer containing pigments and blood vessels.
Functions:
1. Pigment absorbs excessive rays of light preventing their reflection within eye.
2. Blood vessels supply food and O2 to cells of retina.
Ciliary body:
Structure:
Thickened part is an extension of choroid and contains ciliary muscles.
Functions:
1. Ciliary muscles play an NB role in controlling the curvature of the lens during accommodation.
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