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Accessory structures of the eyes. |
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Eyebrows/eyelashes: Protective. Eyelids: Protective lacrimal glands:tears wash out dirt Conjunctivae: lubricate cornea |
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Eyeball structure The bulk of the eyeball is made of a jelly (vitreous humour) surrounded by three layers of tissue |
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sclera ……fibrous outer layer – protects and gives shape to eyeball
choroid – rich in blood vessels; nourishes the retina; absorbs light rays retina ……rich in photoreceptors & nerves – image formation These layers develop into special structures at the front of the eyeball. The sclera becomes the cornea and the choroid becomes the ciliary body (process and muscle) and iris |
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| Bends light; circulates & nourishes front of eye | |
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bends light, maintains eye shape. |
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Formation of an image on the retina involves three processes |
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1. refraction or bending of light rays 2. formation of an inverted image on the retina (the brain readily reinverts it) 3. adjustments for close vision (accomodation) |
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conjunctivitis - inflammation of conjunctivae (blood shot eyes) cataract – increased opacity of lens/cornea short (near)sightedness – eyeball too long; rays focused in front of retina astigmatism – uneven surface of lens/cornea; difficult to focus clearly |
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two types of photoreceptor |
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Rods & cones; rods are most numerous The rod cells give us black and white vision The cone cells can absorb red, blue or green light depending on the type of photo-pigment protein present. Deficiency of pigment leads to colour-blindness |
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Increased pressure inside the eye caused by decreased drainage of aqueous humor compresses the retinal blood vessels |
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ears perform two sensory functions: |
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Gross structure of the ear. |
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· outer ear - auricle, auditory canal to tympanic membrane · middle ear- cavity between eardrum and inner ear containing ossicles. · inner ear - a complex of bony tunnels lined with a membrane |
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Fluid inside the inner ear. |
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Rotational movement of the head will cause endolymph fluid to move within the semicircular canals to varying extents. This is detected by receptor structures called ampullae , located on the membrane at the base of each of the three canals |
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hair cells. Similar receptor cells are located in two sacs within the vestibule Both sets of receptors send information via the vestibular nerve to the cerebellum, a region of the brain important for coordination of movement |
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- located in the cochlea of the inner ear.
- hair cells
This whole sensory structure is known as the organ of corti or spiral organ. |
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- Summary of the Mechanism of Hearing
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- vibration of tympanic membrane (eardrum)
- amplified by the ossicles (3 bones in the middle ear)
- vibration of the oval window
4. Movement of perilymph (fluid in the cochlea) 5. Movement of endolymph (fluid in the cochlear duct) 6. Hair cells on the organ of corti (spiral organ) move relative to the membrane above 7.the hairs bend 8. Electrical activity in the hair cells 9. Nerve impulse (cochlear nerve) 10. Translated in the cerebral cortex and perceived as sound. |
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