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Summary sensory organs
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sensory organs summary
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SENSORY ORGANS: THE EYEAND EA
I. POSITION AND PROTECTION OF THE EYE
- eyeball around 2.5cm in diameter
- Protected by bony cavity in the skull = Orbit (lined with adipose tissue)
- protect eye from mechanical damage
- Eyebrows = protect against dust, sweat and foreign bodies
- Eyelashes and eyelids = respond to reflex closure when eye exposed to bright
light
- Tears = secreted by lachrymal glands.
- wash away irritating dust and grit
- keep conjunctiva moist
- contain lysosome enzymes which acts as an anti-microbial
- Glands og meiboom = oily secretion which mixes with tears
- lubricate eyes and prevent dehydration
EXTERNAL FEATURES
OF THE EYE
II. EYE MUSCLES
- 3 pairs = hold eyeball in position
- side to side
- up and down
- at an angle
- voluntary muscles but also require autonomic control for coordination ,
convergence and accommodation
III. BINOCULAR VISION
- co-ordination of eye muscles ensure eyes work together to focus on objects
- each eye sees from different angle
R
, - images from 2 eyes fused in cerebrum so that only one image perceived - this is
called binocular/stereoscopic/3D vision.
- this enables us to see depth and distance
IV. PUPILLARY MECHANISM (REFLEX ACTION)
- IN BRIGHT LIGHT:
- Circular muscles of iris contract
- Radial muscles relax
- Pupil constricts
- Amount of light entering eye reduces
- IN DIM LIGHT:
- Radial muscles of iris contract
- Circular muscles relax
- Pupil dilates
- Amount of light entering eye increases
V. ACCOMODATION
- process by which the lens becomes more convex (fatter) so that incoming light rays
from objects closer than 6m are bent for clear focusing
- rays must be bent to produce a sharp, clear image on retina
- lens must become fatter to refract more light
NEAR VISION PROCESS:
1. ring of ciliary muscle contract
2. less pull placed on suspensory ligaments (they slacken)
3. slack ligaments don't pull lens
4. elastic lens becomes convex (fatter)
5. more light refracted to bring focus onto retina
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