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Organ Systems III MTI Neuroanatomy > Visual System Part IV: Central Visual Pathways > Flashcards

Visual System Part IV: Central Visual Pathways Flashcards

1
Q

T/F?

The visual field is bisected into right and left sides, each side projecting to the ipsilateral of the brain.

A

False. Right and left sides project to the contralateral side of the brain.

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2
Q

How is visual information from the right side of the visual field sent to the left side of the brain?

A 
Partial decussation (crossing) of ganglion cell axons in the optic chiasm. 
i.e. right visual field of right eye and right visual field of left eye go to left LGN and then left primary visual cortex
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3
Q

T/F?

The image in the fovea of the retina is projected in total to both sides of the brain.

A

True.

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4
Q

What causes total blindness in one eye?

A

Lesion of one optic nerve distal to the chiasm.

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5
Q

What is heteronymous hemianopsia? What causes it?

A

Tunnel vision affecting opposite visual fields (ie right field in right eye and left field in left eye affected)

Lesion of central optic chiasm (pituitary tumor)

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6
Q

What is homonymous hemianopsia? What causes it?

A

Tunnel vision affecting same side visual fields (ie left field in right eye and left field in left eye affected)

Lesion of optic system between optic chiasm and visual cortex

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7
Q

What retinal cells project their information along the parvocellular pathway? Magnocellular?

A 
Midget = parvocellular
Parasol = magnocellular
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8
Q

What is the function of the parvocellular pathway?

A

Object perception and identification. “What”

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9
Q

What is the function of the magnocellular pathway?

A

Perception of motion and direction relative to self to enable operating in your environment. “Where”

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10
Q

Parvo or Magno?

90% of axons in optic nerve devoted to this

A

Parvo

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11
Q

Parvo or Magno?

Receives info from larger group of PRs (esp rods in periphery)

A

Magno

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12
Q

Parvo or Magno?

Receive input from 1 or a few PRs (esp cones in fovea)

A

Parvo

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13
Q

Parvo or Magno?

High acuity with smaller center-surround receptive fields.

A

Parvo

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14
Q

Parvo or Magno?

Respond to movement with low spatial resolution - dark or night vision.

A

Magno

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15
Q

Parvo or Magno?

Sensitive to color and shape

A

Parvo

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16
Q

Six layered structure in thalamus that receives input from each eye in alternating layers.

A

Lateral geniculate nucleus

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17
Q

Parvo and magno pathways project their small and large receptive field fields to (different or same) sections of the LGN.

A

Different

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18
Q

Describe the organization of the visual cortex.

A

V1. Primary visual cortex. Medial occipital lobe
V2, V3, V5. Concentric cortical areas extend out from V1
LGN sends axons back to V1.

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19
Q

Broadman’s area 17 corresponds to what area of the visual cortex?

A

V1 (primary visual cortex)

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20
Q

What is the job of the Primary Visual Cortex (V1)? What types of cells are involved?

A

Develops perception of form, color, direction of movement and binocular vision
Simple and complex cells

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21
Q

What is one way that simple cell receptive fields in V1 are different from receptive fields in the retina?

A

V1 RFs - oval

Retinal RFs - round

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22
Q

What inputs are gathered by a simple cell?

A

Combine input from several geniculate cells that individually respond to contiguous points along the bar of light

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23
Q

What do simple cells respond to?

A

Bars of light with specific orientations, directions of movement, and exact location within RF. Respond to edges.

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24
Q

How are complex cells similar to simple cells?

A

Complex and simple cells both respond to a properly oriented edge or bar of light

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25
Q

How are complex cells different from simple cells?

A

Complex cells respond anywhere within the RF.

Complex cells combine the info. of several simple cells and detect the position and orientation of a structure

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26
Q

What is the function of hyper-complex cells?

A

Detect endpoints and crossing lines from information about position and orientation

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27
Q

What integrates info. from simple, complex, and hyper complex cells to generate a sensibility of familiar objects?

A

V2 Association (secondary) cortex

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28
Q

Visual cortices ________ (construct/deconstruct) visual images ____ (into/from) varients of orientation, contrast, and shape.

A

Deconstruct/into

29
Q

What are visual cortical columns?

A

Vertical zones of cortex that use combinations of simple and complex cells to sort information into various properties (color, shape, size, direction, orientation of edges, R or L eye)

30
Q

How is color information organized and understood by the visual cortex?

A

Color red/grn or blu/yel center-surround RFs from retina and LGN are sorted into regions called “blobs”
Blobs are inserted within cortical columns and process color info to form perception

31
Q

For each say T/F regarding binocular vision:
A. You must have binocular vision for depth perception
B. Binocular clues include convergence of the eyes and retinal disparity
C. Involves simple cells in upper & lower layers of LGN.
D. The greater the retinal disparity, the greater the depth.

A

A. False. Depth perception w/ one eye uses visual clues (linear perspective, shading, relative motion, etc)
B. True
C. False. Complex cells in the upper and lower layers of primary and association cortex. V1, V2
D. True.

32
Q

What are the two sources of feedback to the LGN that help shape sensory input?

A
  1. Cortical columns

2. Brainstem (reticular formation) pathways using NEPI, Serotonin, ACh, and NO

33
Q

What is the benefit of cortical feedback to the LGN? What is the effect of this feedback?

A

Allows cortical functions to focus on particular aspects of environment to guide behaviors.
Rapid feedback affects what, when & how visual signals are transferred to cortex.
Regulates how much information comes into a neuron (homeostasis)

34
Q

How does cortical feedback affect firing rates in LGN neurons? What is the mechanism?

A

Feedback = LGN responses more discrete (acuity)
W/o feedback = Generalized activity, few gaps

Alters lateral-inhibition-like mechanisms among LGN neurons.

35
Q

What is the mechanism by which cortical feedback to LGN aids in “recruitment” of LGN cells to respond to a stimulus?

A

Cortical cells that respond optimally to X will sharpen the responses of any LGN cell that responds to X.

  • -> Increases # of LGN cells responding to X
  • -> Enhances LGN-cortical transmission of info.
  • -> Generates synchrony among cortical neurons = more responsive
36
Q

T or F?

The visual cortex can override visual input. It can focus activity according to expectations and ignore variations.

A

True.

37
Q

How do brainstem pathways modulate LGN cells? What specific area of the brain is involved?

A

Reticular formation (brain stem) releases
nEPI, Serotonin, ACh, NO
ACh & NO stimulate LGN and cortex. Make cortical cells more responsive to light.

38
Q

Modulatory activity by brainstem pathways (nEPI, ACh, Serotonin, NO) shifts the brain between _______ and _______ states.
This also allows for what affect on the thalamus?

A

Sleeping and waking

Wakes up thalamus for increased attention and focused activity

39
Q

Reticular formation

A

Region of brainstem that sends out “wake up” signal to cortex so that it can focus on something.

40
Q

Parvocellular and magnocellular pathways meet in what region of the brain?
The information is put into what type of memory?

A

Prefrontal cortex

Working memory

41
Q

What region of the brain is associated with the dorsal pathway? Ventral?

A 
Dorsal = posterior parietal cortex
Ventral = association cortices, including inferotemporal gyrus
42
Q

Role of V1 cortex

A

Projects orientation, spatial frequency, color to association cortices

43
Q

Role of V2 cortex

A

Angles
Contours
Figure/ground

44
Q

Role of V4 cortex

A

Color

More complex shape attributes

45
Q

T or F? The inferotemporal cortex responds to _______
A. Responds to faces and emotional expression
B. Responds to simple geometric shapes
C. Responds to scale and position invariance
D. Responds to one half of the visual field

A

A. True
B. False. Responds to shape/color of complex shapes
C. True.
D. False. Responds to both halves. (info transmitted by interhemispheric axons via the corpus callosum)

46
Q

Role of middle temporal (MT) cortex

A

Part of dorsal stream

Detect complex, global motion

47
Q

T or F? Characteristics of the inferotemporal cortex.
A. The convergence of simple and complex cells determines what IT neurons will respond to.
B. IT neuron activity is modulated by what is focused on.
C. IT cells show only short term memory for visual stimuli.

A

A. True
B. True.
C. False. Both short or long term memory for visual stimuli and their selectivity can be modified by experience.

48
Q

Limbic structures responsible for consolidating memory into cortex. Control level of familiarity and emotional importance.

A

Hippocampus and amygdala

49
Q

What is visual neglect syndrome? Are people who suffer from this condition aware of their vision loss?

A

Loss of function in the right visual association cortices.

No, they are not aware of their vision loss.

50
Q

Part of the brain that aids in face recognition, esp with emotional weight (connection to amygdala). Provides strongest emotional context and enables reactions before consciousness.

A

Fusiform gyrus

51
Q

Hereditary condition where one experiences different modalities simultaneously, eg. sees numbers as having a specific color. Possibly caused by cross reaction of color coded and number neurons in the fusiform gyrus.

A

Synesthesia

52
Q

Inappropriate activity of the fusiform gyrus can lead to _________________ that are created by overreactivity/malfunction of the reticular formation.

A

Visual hallucinations

53
Q

Two types of secondary visual pathways that enable non-conscious visual responses and behavior.

A

Konicellular

Melanopsin

54
Q

T or F? Konicellular ganglion cells - Konicellular Pathway
A. KGCs –> sup. colliculus. –> brain stem & spinal cord –> cortex –> eye movements (incl. saccades)
B. KGCs –> sup. coll. –> pulvinar –> brain stem & spinal cord –> circadian rhythms
C. KGCs are also involved in pupillary reflex and emotion.

A

A. False. KGCs –> sup colliculus –> pulvinar –> cortex –> eye movements (incl saccades)
B. False. Function is head turning (rest is correct)
C. False. Blindsight, Emotion. Pupillary reflex is part of Melanopsin pathway

55
Q

Where do melanopsin ganglion cells project to? What is their function?

A

Pretectum - pupillary reflex

Suprachiasmatic nucleus - circadian rhythms

56
Q

What is / where is Superior Colliculus?

A

Laminar structure on post. surface of midbrain

57
Q

What are the inputs to the konicellular pathway?

A

Retinal konicellular ganglion cells. Moderate spatial resolution, large receptive fields, no center-surround fields.
Visual, auditory, association and motor areas of cerebral cortex.

58
Q 
T or F: Saccadic eye movements
A. Quick simultaneous movements of both eyes in same direction
B. Initiated by Sup. Coll only
C. Modulates CN III, IV, and VI activity
D. Vision is continuous as you scan
A

A. True
B. False. Sup. Coll or by cortex
C. True
D. False. Vision is fixated between the saccades (start/stop as you scan). Seeing occurs only during pauses not during movements.

59
Q

What is the difference between reflexive and scanning saccade?

A

Reflexive saccade triggered exogenously by peripheral stimulus to orient your vision
Scanning saccade is triggered endogenously for the purpose of exploring the visual environment or reading.

60
Q

T or F: Blindsight
A. Lesion of V1 –> lose consciousness of visual info.
B. “Extrastriate” midbrain pathway
C. KGCs –> LGN –> V1 –> post. parietal cortex and amygdala
D. Associated with primitive visual system, “automatic pilot,” newborn reflexes

A

A. True
B. True
C. False. KGCs –> Sup Coll. –> Pulvinar nucleus –> post parietal cortex and amygdala (BLINDSIGHT SKIPS LGN/V1)
D. True

61
Q

Externally/Internally?
_________ perceived things involve activation of mostly occipital and inferotemporal.
_________ perceived things involve activation of mostly frontal and parietal areas.

A

Externally - occipital and inferotemporal

Internally (mind’s eye) - frontal and parietal

62
Q

T or F: Visual Hallucinations
A. Named Charles Bonnet Syndrome (CBS)
B. Hallucinations of faces associated with increased activity of inferotemporal face area
C. Hallucinations of colors associated with increased activity of human color center in V4.
D. ACh and Serotonin deficiencies influence anterior ventral temporal regions more than occipital areas, resulting in complex hallucinations.

A

A. True
B. False. Fusiform face area
C. True
D. True

63
Q

Melanopsin-containing retinal ganglion cells project to ________________________
Melanopsin is most sensitive to______ light
Light absorption initiates action potentials __________ directly or indirectly (through rods and cones)

A

Suprachiasmatic nucleus (SCN)
Blue
Directly

64
Q

T or F: Circadian rhythms
A. Paraventricular nucleus (PVN) is pacemaker of circadian rhythms “master clock”
B. Suprachiasmatic nucleus (SCN) regulates pineal release of melatonin via parasympathetic system.
C. Melatonin regulates various organs and hormones either directly or via SCN.
D. Melatonin is released at night.

A

A. False. Suprachiasmatic nucleus is pacemaker. It projects to PVN.
B. False. Sympathetic
C. True
D. True

65
Q

What happens in the pupillary light reflex?

A

Reflexive constriction of both pupils in response to light shown in one eye.

66
Q

What is the pathway of nerve impulses in the pupillary light reflex?

A

Light –> melanopsin ganglion cells –> Pretectal n. –> EW nucleus –> Ciliary ganglion –> Pupil

67
Q

What is the sympathetic response of the eye and eyelid? What is the pathway? What would cause this to happen?

A

Dilate pupil, raise eyelid
T1, T2 –> Superior cervical ganglion cells –> dilator pupillae and tarsal muscle
THERE IS NO SYMPATHETIC CONTROL OF CILIARY MUSCLE/LENS
happens b/c of local reflexes & emotional state

68
Q

Damage to some elements of the sympathetic nervous system can inhibit the ___________ muscle, causing droop (ptosis). This is seen in __________ syndrome.

A

Tarsal

Horner’s

Organ Systems III MTI Neuroanatomy (5 decks)

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