1. Special Senses
Chapter 8

2. Layers forming the wall of the eyeball
Fibrous layer
Outside layer
Vascular layer
Middle layer
Sensory layer
Inside layer

3. Extrinsic eye muscles
Six muscles attach to the outer surface of the eye
Produce eye movements

4. Photoreceptors
Inner neural layer contains receptor cells (photoreceptors)
Rods: more numerous (120 million)
Cones (6-7 million)

5. Photoreceptors
Signals pass from photoreceptors via a two- neuron chain
Bipolar neurons
Ganglion cells

6. Photoreceptors

7. Photoreceptors
Signals leave the retina toward the brain through the optic nerve
Optic disc (blind spot) is where the optic nerve leaves the eyeball
Cannot see images focused on the optic disc

9. Photoreceptors
Rods

10. Photoreceptors
Cones

12. Cone sensitivity Three types of cones
Sensitive to different wavelengths

15. Colorblindness: lack of one cone type
the result of the lack of one cone type

16. Rods vs. Cones

17. Photoreceptors
No photoreceptor cells are at the optic disc (blind spot)
BLIND SPOT TEST

18. Cataracts Result when the lens becomes hard and opaque with age
Vision becomes hazy and distorted
Eventually blindness

19. Chambers of Eye (segments)
Anterior (aqueous) Anterior to the lens
Contains aqueous humor
Posterior (vitreous) Posterior to the lens
Contains vitreous humor

20. Posterior Wall of Retina

21. Pathway of light through eye
The eye is set for distance vision (over 20 feet away)
The lens must change shape to focus on closer objects (less than 20 feet away)
Accommodation

22. Pathway of light through eye
Image formed on the retina is a ‘real image’
Reversed from left to right
Upside down
Smaller than the object

23. Visual Fields and Visual Pathways