Lecture 8: Vision II Flashcards
1
Q
List in order the cellular layers of the retina.
A
- Photoreceptors
- Horizontal cells
- Bipolar cells
- Amacrine cells
- Ganglion cells
2
Q
Which cells make up the photoreceptor retinal layer?
A
- rods
- cones
3
Q
What does photoreceptors do?
A
Transmit signals to outer plexiform layer.
** plexiform layer = layer of synaptic connections **
4
Q
What type of cells does the photoreceptors synapse with?
A
- Bipolar Cells
- Horizontal Cells
5
Q
Where do horizontal cells transmit signals to?
A
- Transmit signals from rods and cones to bipolar cells
- Transmit signals to outer plexiform layer
6
Q
Is the output of horizontal cells inhibitory or excitatory?
A
Output is always inhibitory (lateral inhibition).
7
Q
Where do bipolar cells transmit signals to?
A
- Transmit signals from rods, cones, and horizontal cells.
- Transmit signals to inner plexiform layer.
8
Q
Which cells do bipolar cells synapse with?
A
- Amacrine cells
- Ganglion cells
9
Q
What signals do amacrine cells transmit?
A
- Transmit signals:
- directly from bipolar to ganglion cells
- within inner plexiform layer from axons of bipolar cells to dendrites of ganglion cells or to other amacrine cells
10
Q
Which type of cells in the retinal layers transmits signals from the retina to the brain?
A
Ganglion Cells !!!!!
11
Q
What do the axons of ganglion cells make up?
A
Optic Nerves
12
Q
What are the only retinal cells that transmit action potentials?
A
Ganglion Cells
13
Q
Except for ganglion cells, what type of conduction does the other cell types use?
A
Electrotonic conduction which allows graded conduction of signal strength.
14
Q
What do interpexiform cells do?
A
transmit from inner plexiform layer to outer plexiform layer (retrograde)
15
Q
Are interplexiform cells involved in lateral inhibition?
A
Yes - fine tune original image that is picked up by the rod and cone cells.
16
Q
What are the four neurons that compose pure rod vision?
A
- rods
- bipolar cells
- amacrine cells
- ganglion cells
17
Q
In the foveal region, what are the three neurons that compose the direct pathway?
A
- cones
- bipolar cells
- ganglion cells
18
Q
Which neurotransmitter goes from the rod and cones to bipolar cells?
A
Glutamate
19
Q
Which neurotransmitters are released from amacrine cells?
A
- GABA
- glycine
- dopamine
- acetylcholine
- indolamine
**they are ALL INHIBITORY**
20
Q
What are the functions of amacrine cells?
A
- About 30 kinds:
- one type is part of direct pathway for rod conduction
- one type responds strongly to onset of continuing visual signal but fades rapidly
- some types respond strongly at the offset of visual signals, but the respone fades rapidly
- some respond when a light is turned on or off
- one type responds to movement of a spot across the retina in a specific direction
- THEREFORE, MOST AMACRINE CELLS ARE INTERNEURONS THAT HELP ANALYZE VISUAL SIGNALS BEFORE THEY LEAVE THE RETINA!
21
Q
What are the 3 types of ganglion cells?
A
W, X, and Y
22
Q
How many rods and cones converge on each ganglion cell and the optic nerve fiber from the ganglion cell?
A
Average 60 rods and 2 cones.
23
Q
What happens to the number of rods and cone that converge on each ganglion cell as you approach the fovea?
A
Fewer rods and cones converge on each optic fiber and rods and cones become more slender:
- increased visual acuity in central retina
- in central fovea there are only slender cones ( about 35,000) and NO rods.
24
Q
Is the peripheral retina more sensitive to weak light?
A
Yes - thus night vision is better out of the corner of your eye.
- As many as 200 rod converge on a single optic fiber in the more peripheral regions of the retina.
25
What percentae of ganglion cells are made up of W type and what is its function?
* 40%
* Small
* Transmit signals 8 m/sec
* Receive most of their excitation from rods transmitted by way of small bipolar cells ad amacrine cells
* They have broad fields in the peripheral retina because their dendrites spread widely in the inner plexiform layer.
26
How do W ganglion cells receive most of their excitation?
From rods transmitted by way of smal bipolar cells and amacrine cells.
27
Why do W ganglion cells have broad fields in the peripheral retina?
Because their dendrites spread widely in the inner plexiform layer.
28
What percentage of ganglion cells are made up of X-type and what are their functions?
* 55%
* Medium diameter
* Transmit signals 14 m/sec
* They have small fields
* signals represent discrete retinal locations
* Every X ganglion cell receives input from at least one cone cell; therefore, probably responsible for ALL color vision.
29
Which type of ganglion cell is probably responsible for ALL color vision?
X ganglion cells
30
Do X-ganglion cells have a small or large field in the retina?
Small - signals represent discrete retinal locations.
31
What percetage of ganglion cells are made up of Y-type cells and what is their function?
* 5%
* Large diameter
* Transmit signals 50 m/sec or faster
* Respond to rapid changes in visual image
* Presumably apprise the CNS almost instantaneously when a new visualevent occurs anywhere in the field without great accuracy with respect to location of field.
32
Which ganglion cell type presumably apprise the CNS almost instantaneously when a new visual event ocurs anywhere in the field without great accuracy with respect to location of field?
Y Ganglion Cells
33
What is the function of the dorsal lateral geniculate nucleus?
* Receives input from the optic nerve
* Relays information from optic tract to visual cortex by way of optic radiation (geniculocalarine tract).
34
How much decussation occurs in the optic chiasm?
50% decussation in optic chiasm.
35
How many nuclear layers make up the lateral geniculate nucleus?
6 nuclear layers in lateral geniculate nucleus.
* II, III, V receive signals from lateral half of ipsilateral retina
* I, IV, VI receive signals from medial half of opposite retina
36
Where do layers II, III, and V of the lateral geniculate nucleus receive signals from?
Lateral half of ipsilateral retina
37
From where does layers I, IV, and VI of the lateral geniculate nucleus receive signals from?
medial half of opposite retina
38
Where does the dorsal lateral geniculate nucleus relay information from and to?
* From Optic Tract
* To Visual Cortex by way of the optic radiation (geniculocalcarine tract)
39
Where does the left visual cortex get visual information from?
Temporal field of the left eye and the nasal field of the right eye.
40
Where does the right visual cortex receive visual information from?
Temporal field of the right eye and the nasal field of the left eye.
41
What kind of neurons do layers I and II of the dorsal lateral geniculate nucleus contain?
Large Neurons
42
Which layers of the dorsal lateral geniculate nucleus are considered the magnocellular layers?
Layers I and II
43
What type of cell do layers I and II of the dorsal lateral geniculate nucleus receive input almost entirely from?
Large Y type ganglion cells.
44
Which layers of the dorsal lateral geniculate nucleus transmit only black and white?
Layers I and II
45
Is point to point transmission poor in layers I and II of the dorsal lateral geniculate nucleus?
Yes
46
What do layers I and II of the dorsal lateral geniculate nucleus provide?
Provides rapidly conducting pathways to visual cortex.
47
Which layers of the dorsal lateral geniculate nucleus are considered parvocellular layers?
layers III through VI (3, 4, 5, and 6)
48
What size of neurons do layers III through VI of the dorsal lateral geniculate nucleus contain?
Small to medium-size neurons.
49
Which type of ganglion cell do layers III through VI of the dorsal lateral geniculate nucleus receive input almost entirely from?
X-type ganglion cells.
50
What do layers III through VI of the dorsal lateral geniculate nucleus provide?
Provides moderate conducting pathway to visual cortex.
51
Does layers III through VI of the dorsal lateral geniculate nucleus have accurate point to point transmission?
Yes
52
What is tranmission gating in the dorsal lateral geniculate nucleus?
Lateral geniculate nucleus controls how much of the signal is allowed to pass to the cortex.
53
What are the 2 sources of gating control in the dorsal lateral geniculate nucleus?
* Corticofugal fibers from primary visual cortex
* Reticular areas of the mesencephalon
\*\*Both of these sources are inhibitory and help highlight visual information that is allowed to pass\*\*
54
What is another name for the primary visual cortex?
Striate Cortex
55
Where is the primary visual cortex located?
Occipital Lobes
56
Where do geniculocalcarine fibers of the primary visual cortex terminate mainly?
Layer IV
57
How many layers make up the primary visual cortex?
Six Distinct Layers
58
In the primary visual cortex, where do signals from the more peripheral retina terminate?
At or in concentric half circles anterior to the pole but still along the calcarine fissure.
59
In the primary visual cortex, where do signals from the macular area terminate?
Near the occipital pole.
60
In which subdivision of layer IV of the primary visual cortex, where do signals from Y ganglion cells terminate?
Layer IVc-alpha
61
In which of the subdivisions of layer IV of the primary visual cortex do signals from X ganglion cells terminate?
Layer IVc-beta and IVa
62
True or Fasle:
The visual cortex is organized into several thousand vertical columns of neurons.
False - organized into several million vertical columns of neurons.
* diameter = 30 - 50 micormeters
* about 1000 neurons per column
63
What type of special column-like areas are located among the columns of the secondary visual areas?
Color Blobs
64
What do color blobs receive?
Receive lateral signals from adjacent visual columns and are activated specifically by color signals.
65
What specifically activated color blobs?
Color signals
66
What subdivision of layer 4 of the primary visual cortex does fast, black and white signals from Y type ganglion cells terminate in?
IVc-alpha
67
What subdivision of layer 4 of the primary visual cortex does very accurate, color signals from X type ganglion cells terminate in?
IVa and IVc-beta
68
What does the cortical area of the primary visual cotex decipher?
Whether the respective areas of the two visual images from the two separate eyes are in register with each other.
69
What is the deciphered information from the cortical area of the primary visual cortex used for?
To adjust the directional gaze of the separate eyes.
70
What is required for stereopsis?
The deciphering by the coritcal area to whether the respective areas of the two visual images from the two separate eyes are in register with each other.
71
What nerve controls both sets of ciliary muscles?
CN III controls both sets of ciliary muscles (occulomotor nerve).
72
What is the mechanism of accommodation in a young person?
* when the lens is in a relaxed state with no tension on its capsule, it assumes an almost spherical shape.
* suspensory ligaments attached radially around the lens create a tenion that causes the lens to remain relatively flat under normal eye conditions.
* meridional fibers of ciliary muscle contract and release tension of lens
* circular fibers of ciliary muscle also decrease tension on lens
73
Explain accommodation in an older person.
* lens becomes larger and thicker with age
* lens becomes less elastic with age
* power of accommodation decreases to less than 2 diopters by the age of 45 - 50
* it decreases to 0 by the age of 70
* prebyopia
74
