1. Journal #3: Which 3 cranial nerves monitor the tongue?
Objective #3: Explain how light stimulates nerve impulses and trace the visual pathways to the brain.

2. Visual Physiology Notes
Interactive pgs

3. 2 Types of Photoreceptors
Rods:
respond to almost any photon, regardless of energy content
Cones:
have characteristic ranges of sensitivity

4. Photoreceptor
Figure 17–13a

5. Photoreceptor Outer segment with membranous discs Inner segment:
narrow stalk connects outer segment to inner segment

6. Visual Pigments Is where light absorption occurs
Derivatives of rhodopsin (opsin plus retinal)
Retinal:
synthesized from vitamin A

7. Retinitis Pigmentosa (RP)
Collection of inherited retinopathies
Most common inherited visual abnormality
Visual receptors gradually deteriorate
Blindness eventually results

8. Bleaching Rhodopsin molecule breaks down into retinal and opsin
Figure 17–15

9. Night Blindness
Results from deficiency of vitamin A

10. Color Sensitivity
Integration of information from red, green, and blue cones
Figure 17–16

11. Color Blindness
Inability to detect certain colors
Figure 17–17

12. Dark-Adapted State
Most visual pigments are fully receptive to stimulation

13. Light-Adapted State Pupil constricts
Bleaching of visual pigments occurs

14. Visual Pathway Begins at photoreceptors
Ends at visual cortex of cerebral hemispheres
Message crosses 2 synapses before it heads toward brain:
photoreceptor to bipolar cell
bipolar cell to ganglion cell

15. Each Photoreceptor
Monitors a specific receptive field in retina

16. Each Ganglion Cell
Monitors a specific portion of a field of vision

17. M Cells Are ganglion cells that monitor rods Are relatively large
Provide information about:
general form of object
motion
shadows in dim lighting

18. P Cells Are ganglion cells that monitor cones
Are smaller, more numerous
Provide information about edges, fine detail, and color

19. Cones
Provide more precise information about visual image than rods

20. On-Center Neurons Are ganglion cells
Are excited by light arriving in center of their sensory field
Are inhibited when light strikes edges of their receptive field

21. Off-Center Neurons Inhibited by light in central zone
Stimulated by illumination at edges
Figure 17–18

22. Visual Pathway Axons from ganglion cells converge on optic disc
Penetrate the wall of the eye
Proceed toward diencephalons as optic nerve (II)
2 optic nerves (1 for each eye) reach diencephalons at optic chiasm

23. Visual Pathway
Figure 17–19

24. Visual Data
From combined field of vision arrive at visual cortex of opposite occipital lobe:
left half arrive at right occipital lobe
right half arrive at left occipital lobe

25. Depth Perception
By comparing relative positions of objects between left–eye and right–eye images
Figure 17–19