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Neuroscience1 > Visual System > Flashcards

Visual System Flashcards

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
Q

Ganglion cell function

A

Final stage of retinal processing, and transmit info to subcortical visual centers in the brain, axons form optic nerve

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26
Q

Receptive field

A

The area in visual space (or the corresponding area of retinal surface) which upon illumination influences the signaling neuron

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27
Q

Sustained ganglion cells

A

Respond as long as the stimulus remains w/in the receptive field

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28
Q

Transient ganglion cells

A

Respond only when the light is turned on or off

29
Q

P-cells

A

Small ganglion cells that provide info about fine detail and color

30
Q

M-cells

A

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
Q

Topography

A

Each point on retinal surface sees a particular point in the visual field, w/ neighboring retinal points seeing neighboring visual fields

32
Q

Hemifields

A

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
Q

Homonymous

A

Both eyes viewing the same of corresponding visual field

-everything caudal to the optic chiasm is carrying only contralateral Homonymous sensation

34
Q

Hemianopia

A

Loss of visual perception of half of the entire visual field

35
Q

Heteronymous

A

-each individual eye viewing different visual fields

36
Q

Binasal heteronymous Hemianopia (or binasal Hemianopia)

A

Each eye is only able to see the ipsilateral temporal visual fields and not the nasal visual fields

37
Q

Nasal visual hemifield visual pathway

A
  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
Q

Temporal visual hemifield visual pathway

A
  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
Q

Lower hemifield visual pathway

A
  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
Q

Upper hemifield visual pathway

A
  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
Q

Contralateral upper Homonymous Quandrantanopia

A

Myers loop (fibers of upper visual hemifield) is damaged

42
Q

Location of fibers from peripheral vs. central visual fields

A
  • peripheral- more superficially located

- central- more internally located

43
Q

Lateral geniculate nucleus

A

Located at the termination of the optic tracts in the thalamus, composed of 6 layers (magnocellular and parvocellular)

44
Q

LGN- topography

A

Each LGN contains a representation of the contralateral visual hemifield

45
Q

Magnocelluar layer

A

Layer of LGN

Perception of dark and light contrast

46
Q

Parvocellular layer

A

LGN layer

Process fine spatial and color information

47
Q

Branches of fibers off of superior Colliculus

A
  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
Q

Quadrant defects

A

First clue to pathology in silent areas of cortex, especially temporal lobe cortex

49
Q

Macular sparing

A

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
Q

The central visual field is represented by ________ in the primary visual cortex while the peripheral visual field is represented by _______

A

Posterior pole

Anterior portions of the calcarine sulcus

51
Q

Tract through primary visual cortex

A 
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
Q

Areas of temporal lobe function

A

Object recognition

53
Q

Areas in posterior parietal lobe function

A

Perception of motion, rotation, depth

54
Q

Areas in parieto-temporal lobe junction function

A

Perception of color, motion, rotation, depth

55
Q

P pathway

A

cell of LGN responsible for relaying info on form and color of objects to temporal lobe regions

56
Q

M pathway

A

Cell of LGN responsible for relaying info of gross form and motion to parietal lobe areas

57
Q

Lesion of area 17 bilaterally

A

Blindness, although some limited visual capabilities can be present, such as pupillary light reflex

58
Q

Prestriate Cortex (areas 18 and 19) receives info from

A
  • ipsilateral primary visual cortex
  • ipsilateral superior Colliculus
  • contralateral prestriate cortex
59
Q

Prestriate cortex lesion

A

Deficits in discriminating between objects or patterns

60
Q

Posterior half of the middle and inferior temporal gyri receives info from

A

Prestriate cortex and superior Colliculus

61
Q

Posterior half of the middle and inferior temporal gyri visual field

A

First level of system where visual stimuli from both hemispheres are merged into a single image

62
Q

Posterior half of the middle and inferior temporal gyri bilateral lesion

A

Difficulty in identifying salient feature of objects or patterns that distinguish them

63
Q

Area V5

A

Junction of posterior temporal lobe and inferior parietal lobe (p pathway)

64
Q

Area V5 function

A

Form and color recognition, translational movements

65
Q

Brodmann’s areas 20 and 21 location

A

Anterior half of the middle and inferior temporal gyri (p pathway)

66
Q

Brodmann’s area function

A

Memorizing a visual pattern (object recognition)

67
Q

Area V3 (Brodmann’s area 7)

A

Posterior parietal lobe, receives projections from visual association areas (m pathway)

68
Q

Area V3 function

A

Identify rotational and directional movements, visual spatial orientation, position of body in space (depth perception)

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