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Neuroscience1 > Visual System > Flashcards

Visual System Flashcards

(68 cards)

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1
Q

Macula lutea

A

Contains central fovea (pit)

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2
Q

Four cell layers of retina

A
  1. Pigment cell layer
  2. Rods
  3. Cones
  4. Ganglion cell layer
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3
Q

Pigment cell layer

A

Derived from choroid, attaches retina to eye ball, absorbs stray light

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4
Q

Rods

A

Light receptors

Located at periphery of retina, for low light vision & perception of movement

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5
Q

Cones

A

Light receptor
Concentrated in central retina, fovea only contains cones and is the area of max visual acuity, color and brightness discrimination

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6
Q

Ganglion cell layer

A

Myelinated axons of these cells form the optic nerve

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7
Q

Refraction

A
  1. inverted image of the object is focused on the retina

2. Light is refracted by cornea, aqueous humor, lens (where image is inverted) and the vitreous humor

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8
Q

Lens function

A

Changes refractive power by changing shape of lens (rounder for close viewing, flatter for distant)

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9
Q

Lens at rest

A

Lens is held relatively flat by suspensory fibers that connect it to the ciliary muscle

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10
Q

Accommodation

A

Lens increases its refractive power to view a near object by becoming more convex (rounder)

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11
Q

Accommodation steps

A
  1. Ciliary muscle contracts (parasympathetic fibers)
  2. Tension on suspensory fibers is reduced
  3. Lens contracts into a more spherical shape
  4. Can see near objects
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12
Q

Emmetropia

A

Normally occurring condition in which the image of an object is focused on the retinal surface

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13
Q

Hypermetropia

A

(Far- sightedness)

Focal point falls behind the retinal surface

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14
Q

Myopia

A

(Near sidedness)

Focal point falls in front of the retina

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15
Q

Presbyopia

A

Loss of lens elasticity noted with age.

Bifocals needed

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16
Q

Bifocals

A

Part of the lens corrects vision for distance and a part that corrects for near vision

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17
Q

Optic disc

A

Produces blind spot, exit of optic nerve

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18
Q

Rod receptor function

A

Used in dim conditions due to low threshold, low rod acuity

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19
Q

Cones receptor function

A

Used in high light conditions due to high threshold, high acuity and provides color vision

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20
Q

Color vision

A

3 different cones: blue, green, red are sensitive to different wavelength of light
-perception of other colors is due to the relative excitation of the different cones

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21
Q

Color blindness

A

Result of absence of one or more cone populations

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22
Q

Neural coding of visual signals

A

Potentials in receptors are transmitted to bipolar cells and then altered by other cells in the retina through: the vertical system or horizontal system

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23
Q

Vertical system function

A

Signals pass from receptors to bipolar cells to ganglion cells

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24
Q

Horizontal system function

A

Horizontal and amacrine cells provide lateral interactions (lateral inhibition) between different vertical system components

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25
Ganglion cell function
Final stage of retinal processing, and transmit info to subcortical visual centers in the brain, axons form optic nerve
26
Receptive field
The area in visual space (or the corresponding area of retinal surface) which upon illumination influences the signaling neuron
27
Sustained ganglion cells
Respond as long as the stimulus remains w/in the receptive field
28
Transient ganglion cells
Respond only when the light is turned on or off
29
P-cells
Small ganglion cells that provide info about fine detail and color
30
M-cells
Large ganglion cells that are primarily concerned with signaling changes in the scene being viewed including: movement, changes in light/dark contrast and basic form analysis
31
Topography
Each point on retinal surface sees a particular point in the visual field, w/ neighboring retinal points seeing neighboring visual fields
32
Hemifields
Visual field can be divided by into a L and R hemifield - each half of brain receives info from contralateral hemifield - separation is accomplished at level of optic chiasm
33
Homonymous
Both eyes viewing the same of corresponding visual field | -everything caudal to the optic chiasm is carrying only contralateral Homonymous sensation
34
Hemianopia
Loss of visual perception of half of the entire visual field
35
Heteronymous
-each individual eye viewing different visual fields
36
Binasal heteronymous Hemianopia (or binasal Hemianopia)
Each eye is only able to see the ipsilateral temporal visual fields and not the nasal visual fields
37
Nasal visual hemifield visual pathway
1. Temporal retina fibers run along lateral edge of optic nerve, chiasm and tract 2. 80% synapse in ipsilateral lateral geniculate nucleus, 20% synapse in sup Colliculus via brachium 3. Terminate in ipsilateral primary visual cortex (area 17, calcarine cortex)
38
Temporal visual hemifield visual pathway
1. Nasal retina fibers run along medial edge of optic nerve 2. Cross in optic chiasm 3. Course along medial optic tract 4. 80% synapse in contralateral LGN and 20% in sup Colliculus 5. Terminate in primary visual cortex (area 17, calcarine cortex)
39
Lower hemifield visual pathway
1. Upper retina fibers run along dorsal edge of optic nerve, chiasm, tract 2. Synapse in LGN 3. Run directly around lateral ventricle 4. Terminate in superior calcarine fissure at the cuneus
40
Upper hemifield visual pathway
1. Lower retina fibers run along ventral optic nerve, chiasm, tract 2. Synapse in LGN 3. Run around temporal horn of lateral ventricle 4. Run inferiorly through temporal lobe to reach inferior calcarine fissure- lingual gyrus
41
Contralateral upper Homonymous Quandrantanopia
Myers loop (fibers of upper visual hemifield) is damaged
42
Location of fibers from peripheral vs. central visual fields
- peripheral- more superficially located | - central- more internally located
43
Lateral geniculate nucleus
Located at the termination of the optic tracts in the thalamus, composed of 6 layers (magnocellular and parvocellular)
44
LGN- topography
Each LGN contains a representation of the contralateral visual hemifield
45
Magnocelluar layer
Layer of LGN | Perception of dark and light contrast
46
Parvocellular layer
LGN layer | Process fine spatial and color information
47
Branches of fibers off of superior Colliculus
1. Prestriate visual areas around PVC (areas 18 & 19) 2. Nucleus of the pretectal area rostral to superior Colliculus- afferent pupillary light reflex 3. Oculomotor complex- constriction of pupil 4. T1 and T2 intermediolateral cell column - dilation of pupil
48
Quadrant defects
First clue to pathology in silent areas of cortex, especially temporal lobe cortex
49
Macular sparing
Field defects which include everything except macular field (central vision) - occurs when entire ipsilateral visual cortex is destroyed except for occipital pole - occipital pole (foveal representation) receives an overlapping blood supply
50
The central visual field is represented by ________ in the primary visual cortex while the peripheral visual field is represented by _______
Posterior pole | Anterior portions of the calcarine sulcus
51
Tract through primary visual cortex
``` Areas 18 and 19 then: -temporal lobe -posterior parietal lobe -parieto-temporal lobe Allow us to perceive visual space (depth and movement) & object specificity (color and form) w/in visual space ```
52
Areas of temporal lobe function
Object recognition
53
Areas in posterior parietal lobe function
Perception of motion, rotation, depth
54
Areas in parieto-temporal lobe junction function
Perception of color, motion, rotation, depth
55
P pathway
cell of LGN responsible for relaying info on form and color of objects to temporal lobe regions
56
M pathway
Cell of LGN responsible for relaying info of gross form and motion to parietal lobe areas
57
Lesion of area 17 bilaterally
Blindness, although some limited visual capabilities can be present, such as pupillary light reflex
58
Prestriate Cortex (areas 18 and 19) receives info from
- ipsilateral primary visual cortex - ipsilateral superior Colliculus - contralateral prestriate cortex
59
Prestriate cortex lesion
Deficits in discriminating between objects or patterns
60
Posterior half of the middle and inferior temporal gyri receives info from
Prestriate cortex and superior Colliculus
61
Posterior half of the middle and inferior temporal gyri visual field
First level of system where visual stimuli from both hemispheres are merged into a single image
62
Posterior half of the middle and inferior temporal gyri bilateral lesion
Difficulty in identifying salient feature of objects or patterns that distinguish them
63
Area V5
Junction of posterior temporal lobe and inferior parietal lobe (p pathway)
64
Area V5 function
Form and color recognition, translational movements
65
Brodmann's areas 20 and 21 location
Anterior half of the middle and inferior temporal gyri (p pathway)
66
Brodmann's area function
Memorizing a visual pattern (object recognition)
67
Area V3 (Brodmann's area 7)
Posterior parietal lobe, receives projections from visual association areas (m pathway)
68
Area V3 function
Identify rotational and directional movements, visual spatial orientation, position of body in space (depth perception)

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