Exam 10 (CH. 9/10)

Question 1

What cells have axons that leave the retina?

Answer 1

Retinal Ganglion Cells (RGC)

Question 1

-What are the types of photoreceptor? Compare and contrast their structure and function.

Answer 1

• Rods and cones
• Rods are long and cylindrical in shape. They are more numerous than cones and are mainly located in the peripheral regions of the retina. Rods contain a pigment called rhodopsin, which is sensitive to low levels of light. Rods are responsible for vision in dim light conditions (scotopic vision). They are highly sensitive to light and can detect even small amounts of light. However, rods do not provide color vision or sharp visual details.
• Cones are shorter and conical in shape. They are less numerous than rods and are mainly concentrated in the central region of the retina called the fovea. Cones contain three different types of pigments, each sensitive to different wavelengths of light (red, green, and blue).
  Cones are responsible for color vision and visual acuity in bright light conditions (photopic vision). They are less sensitive to light compared to rods but provide better visual acuity and the ability to perceive colors.

Question 2

-What is the structure of the retina? Describe the functionally relevant details.

Answer 2

from most superficial to deep the layers include:
1. layer of cell bodies of retinal ganglion cells (axons)
2. inner plexiform and inner nuclear layer which includes multiple cell bodies including bipolar, horizontal, amacrine
3. outer plexiform layer and outer nuclear layer
4. light sensitive layer - photoreceptor outer segments pointing to the back of your head
5. pigmented epithelium

Question 3

Describe the structure of the eye – what provides most of the focusing power?

Answer 3

cornea

Question 4

-What is the optic disk?

Answer 4

the beginning of the optic nerve

• the point at which retinal ganglion cells come together
• entry point for the major blood vessels supplying the retina
• this area is your built in blind spot
  -there are no photoreceptors, interneurons, or ganglion cells in this area. our nervous system fills in the blind spot for us

Question 5

What is the pathway from retina to primary visual cortex? Know the cells along the way. Also, know the
decussations, and what fibers are crossing (and explain why).

Answer 5

retina-> retinal ganglionic cells -> bipolar, horizontal, and acriman cells -> photoreceptors -> ganglion axons collect in a bundle called the optic disk -> emerge from the back of the eye as the optic nerve -> optic chiasm -> optic tract -> many cells terminate in the LGN (Lateral Geniculate Nucleus) in the dorsal aspect of the thalamus -> visual cortex (V1 also known as Area 17, the posterior portion of the occipital lobe)
- the decussation (crossing, usually in an X) of the visual pathway occurs in the optic chiasm

• the nasal retinal space crosses to supply the contralateral side with that visual field
• temporal retinal space stays on ipsilateral side

Question 6

What is the organization of the LGN?

Answer 6

6 Layers
Layers 1,4,6 are from contralateral eye (opposite)
Laters 2,3,5 are from ipsilateral eye (same)

How it projects:
-Right Temporal Retina= Right LGN
-Left Nasal Retina= Right LGN
-Right Nasal Retina= Left LGN
-Left Temporal Retina= Left LGN

3-6 are Small cell type (P and parvocellular)
1-2 are large (magnocellar and Mtype)

Question 7

What is an off-center/on-surround receptive field? What about on-center/off-surround? What does this
mean functionally?

Question 8

What would lesions to this pathway at different points cause in terms of vision problems?

Answer 8

cut the chiasm?
- lost temporal/peripheral space
cut optic tract?
- lost opposite visual space.
cut dorsal part?
- lose ventral visual space

Question 9

-How is the spatial arrangement of visual information maintained throughout the pathway (what is it called)?

Question 10

What are the dorsal and ventral visual pathways concerned with? What is an example of each?

Answer 10

dorsal stream is the “where” pathway: processing visual motion, where things are at in space

• ventral stream is the “what” pathway: processes color, what shape, what is the identity of the stimuli
• ventral stream” layers 3-6 of the LGN; small ganglion cells
• “dorsal stream”
  layers 1 and 2 of the LGN; sensitive to movement and contrast; larger ganglion cells

Question 11

What are ocular dominance columns, orientation selectivity, and directional selectivity?

Answer 11

• stripes of neurons in the visual cortex that respond preferentially to input from one eye or the other
• these cells are tuned to different angles to help us identify the edges of objects
  allows you to know the orientation of an object
  on set/off surround sharpens the image
• cells discharge in response to left-right OR right-left stimulus movement

Question 12

Where does information from both eyes first become integrated?

Answer 12

optic chiasm; the crossing fibers