Wednesday, February 1, 2012

Objective 2.86 - The Eye

Iris Reflexes: 

2.86 describe the structure and function of the eye as a receptor.


Sclera - is the tough outer coat, which is the visible white part of the eye. 

Cornea - found at the front of the eye - it is convex + transparent - it lets light into the eye. 

Iris - found behind the cornea - it is a colored ring of tissue and it is pigmented (decided the color of your eye) - its muscles contract and relax to alter the size of its pupil (controlling how much light enters the eye)

Pupil - found in the middle of the iris hole - it lets the light through - it is black because there is no light escaping from the inside of the eye. 

Choroid - is a dark layer found underneath the sclera - it is dark because it contains many pigment cells + blood vessels - the pigment stops light being reflected around inside the eye. 

Retina - is the innermost layer (found underneath the Choroid - this is where light energy is transduces into electrical energy of nerve impulses - the retina contains 2 types of photo-receptor cells, 
a) Rods - sensitive to dim light + black and white 
b) Cones - sensitive to colour 

Fovea - found in the middle of the retina - is a small area concentrated with Cones ( cones give sharper images than rods) 

Optic nerve - is a bundle of sensory nerves found at the back of the eye - they carry impulses from the eye to the brain. 

Blind spot - located where the optic nerve leaves the eye at the back of the Retina - an image cannot be formed here because there are no Rods or Cones here. 

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