Visual Part 4 Flashcards
1
Q
What are two ways in which the visual field is bissected?
A
- partial decussation of ganglion cells at optic chiasm. 2. R and L visual fields project to opposite LGBs and visual cortexes.
2
Q
What is a cause of total blindness in one eye?
A
a lesion of the optic nerve before the optic chiasm
3
Q
What is hemianopsia?
A
loss of half of the visual field
4
Q
What is heteronymous hemianopsia?
A
loss of opposite visual fields due to a lesion at the central optic chiams (eg. from pituitary tumors)
5
Q
What is homonymous hemianopsia?
A
loss of the same visual fields due to a lesion between the optic chiasm and the visual cortex
6
Q
where is the lateral genticulate nucleus?
A
in the thalamus
7
Q
What kind of visual information does the parvocellular pathway transmit?
A
color and shape information for object perception and information
8
Q
What kind of visual information does the magnocellular pathway transmit?
A
movement related information for perception of motion, direction, attention and alerting
9
Q
What kind of information does the koniocellular pathway transmit?
A
low acuity color information to the primary visual cortex for unconcsious visual behavior (eg. blindsight)
10
Q
90% of axons in the optic nerve are a part of what pathway?
A
the parvocellular pathway (P or midget cells)
11
Q
5% of axons in the optic nerve are a part of what pathway?
A
the magnocellular pathway (M or parasol cells)
12
Q
Which pathway is high acuity? the parvocellular or the magnocellular pathway?
A
the parvocellular is high acuity
13
Q
Which visual pathway recieves information mostly from cones?
A
the parvocellular pathway
14
Q
Which visual pathway recieves information mostly from rods and is good in night vision?
A
the magnocellular pathway
15
Q
How many layers does the lateral geniculate nucleus have?
A
six (four parvcellular and two magnocellular)
16
Q
Where is the primary visual cortex (V1)?
A
medial surface of the occipital lobe
17
Q
V2, V3 and V5 are what kind of areas?
A
association visual corteces
18
Q
What do the LGN neurons project to the primary visual cortex?
A
information from the retinal center-surround receptive fields
19
Q
What are four types of information that the primary visual cortex perceives?
A
form, color, motion, binocular vision
20
Q
What do simple cells in the primary visual cortex do?
A
combine input from several geniculate cells that respond to the same bar of light
21
Q
how do simple cell RFs differ from retinal or geniculate RFs?
A
they are more oval/rectangular that retinal/geniculate round RFs
22
Q
How do complex cells differ from simple cells?
A
complex cells can respond to properly oriented edges/bars of light anywhere within the RF
23
Q
What type of cells seem to reflect both parallel paths from the geniculate as well as interactions among simple cells and cortical neurons?
A
complex cells of the PVC (V1)
24
Q
What type of PVC cells detect egdes only?
A
simple cells
25
What type of PVC cells detect position and orientation of a structure?
complex cells
26
What type of cells detect endpoints and crossing lines from position/orientation information?
hyper-complex cells
27
What cortex integrates information from simple, complex and hyper-complex cells to generate object familiarity?
association (secondary) visual corteces
28
What are visual cortical columns?
vertical zones of the cortex that combine simple and complex cells to sort information. used to provide feedback to LGN
29
What kind of information do the cortical columns sort?
edge orientation, color, shape/size, direction of movement and R/L eye dominance
30
How is color perception organized in the retina, LGN and cortical regions?
red-green or blue-yellow center-surrounds that get organized into 'blobs' in the cortex
31
What is stereopsis?
stereopis is binocularity
32
how is depth perception generated?
retinal disparity and binocular input from complex cells in upper and lower layers of primary and association visual cortices.
33
How is depth perception acquired in monocular vision?
visual clues such as interposition, shading, relative size, linear perspective, etc
34
What is the purpose of cortical feedback?
to shape sensory input according to behavior, enhance acuity, altering lateral inhibition-like mechanism. enhances responsiveness to a particular stimulus
35
LGN cells are modified by what structures?
cortical columns and brainstem pathways (from norepi, serotonin, Ach, NO) (reticular formation, eg)
36
How does cortical feedback work?
cortical cells that respond to a specific RF will sharpen the response of corresponding LGN cells. This increases the number of LGN cells responding to the same stimulus, enhancing LGN-cortical transmissions
37
What is the purpose of brainstem pathways that modulate the LGN?
modulate wakefulness, acuity, arousal, attention and focus. shifts between wakefulness and sleep states, eg. responds to intense emotions and flashes of light
38
How does the brainstem communicate with the LGN and the cortex?
NO, ACh released from the parabrachial nucleus in the brainstem. Norepi and serotonin (5-HT) also released from the reticular formation
39
What are the two visual association cortices?
The ventral (parvocellular) stream for color, acuity and object identification. The dorsal (magnocellular) stream for action, object manipulation and "where"/"how".
40
The ventral system receives information from what type of photoreceptors and where does that information go?
from cones, goes to the inferotemporal gyrus for identification of form, color, and "working memory"
41
The dorsal system receives information from what type of photoreceptors?
rods
42
The dorsal and ventral visual association streams form what?
the prefrontal cortex and become "working memory"
43
What does the V1 cortex respond to?
orientation, spatial frequency, color
44
What is the V2 cortex tuned to?
angles between lines, orientation of illusory contours
45
What is the V4 cortex tuned to?
color, complex shape attributes such as corners, outline-shapes (human color center)
46
What is the inferotemporal cortex tuned to?
form, color, scale, position invariance, emotional connections, faces, emotional expression
47
What is the middle temporal cortex tuned to?
complex, global motion (part of the dorsal stream)
48
How is information conveyed to the inferotemporal complex?
from both halves of the visual field, by interhemispheric axons via the corpus callosum
49
How is IT stimulus organized? and how can the IT acuity be affected?
organized by the convergence of simple and complex cells. acuity is modulated by attention
50
What kind of memory is shown in the IT?
short and long term
51
What three structures are responsible for consolidating memory in the cortex?
the hippocampus, the amygdala and the limbic structures
52
What did penfield find while performing neurosurgery on patients with epilepsy?
That stimulation of the IT gyrus cortex can elicit vivid scenes from the past
53
What is visual neglect syndrome?
loss of function in the right visual association cortices. Thus, the patient sees only half of the world, does not recognize or intuit the other half
54
What does the fusiform gyrus do?
face recognition, especially with emotional valence (is connected to the amygdala)
55
Inappropriate activity in the fusiform gyrus can lead to what?
hallucinations
56
What is synesthesia? How is it hypothesized to occur?
hereditary condition in which one experiences different sensations simultaneously. possibly due to cross-activation of neurons in the fusiform gyrus
57
Why are emotional sensations often faster that recognition?
because emotional stimuli bypass the visual cortex and go straight to the fusiform gyrus/amygdala. thus they're faster
58
What are the two secondary visual (non-conscious) pathways? How are they different from conscious visual pathways?
the koniocellular and the melanopsin visual pathways. These differ because they bypass the LGN
59
Koniocellular ganglion cells project to______ and do _____(4)
The superior colliculus. visual orientation, saccades, blindsight, emotion
60
Melanopsin ganglion cells project to_____ and _____. There, they do what?
the pretectum (for pupillary reflex) and the suprachiasmatic nucleus (for circadian rythms)
61
The superior colliculus receives information from:
the retinal koniocellular ganglia and visual, auditory, association and motor cortices.
62
The superior colliculus projects information to:
cortical areas for eye movement (saccadic eye movement) and the brain stem and spinal cord (for head movement)
63
What is the purpose of the koniocellular pathway via the superior colliculus?
to orient the eyes and head to the source of the stimulus
64
How is the reflexive saccade initiated?
exogenously by peripheral stimuli
65
How is the scanning saccade initiated?
endogenously for exploring the environment/reading
66
When does seeing occur in saccadic eye movements?
during the pauses
67
What is blindsight?
a lesion of the primary visual cortex that leads to complete lack of consciousness of visual information. (retain emotional responses, but are unaware of what is being seen)
68
What pathway is proposed to generate blindsight?
the extrastriate/koniocellular pathway (bypasses the PVC). koniocellular ganglions --> SC -->pulvinar nucleus -->posterios parietal cortex (dorsal stream) and amygdala (emotions)
69
What does the pulvinar nucleus do?
conveys emotional stimuli to the amygdala, the cingulate and orbitofrontal cortex for subcortical sensory input to the limbic system.
70
What does the amygdala do?
stimulate norepi pathways from the reticular formation for mental arousal/awareness
71
externally perceived things involve activation of what areas?
specialized visual areas (visual cortex, eg)
72
internally perceived things involve activation of what areas?
mostly frontal and parietal areas, dorso-lateral prefrontal cortex
73
What are three ways that hallucinations can occur?
Charles Bonnet Syndrome, Cholinergic or Serotonergic deficiency
74
What happens in patients with Charles Bonnet Syndrome?
increased activity in the fusiform face area leads to hallucinations of faces and colors (V4 activation)
75
What are the two levels of altered neural activity that are related to hallucinations?
activation of a specific cortex or intercortical connections. neuromodulation of cortical areas by cholinergic/serotonergic pathways from the reticula formation.
76
Does Charles Bonnet Syndrome affect occipital visual or anterior ventral temporal lobe areas more? How does this affect the complexity/simplicity of hallucinations?
CBS affects occipital visual areas more, causing a predominance in simple hallucinations
77
Does cholinergic/serotonergic neuromodulation affect occipital visual or anterior ventral temporal lobe areas more? How does this affect the complexity/simplicity of hallucinations?
influences anterior ventral temporal lobes regions more, resulting in a predominance of complex hallucinations
78
What organic compound do intrinically photosensitive retinal ganglion cells have? What is it's purpose? What do these cells do?
melanopsin, which absorbs blue light for ROS protection. This initiates APs that stimulate circadian rhythm and pupillary reflex
79
intrinsically photosensitive retinal ganglion cells project information to:
the suprachiasmatic nucleus (circadian rhythms) and to the pretectum (pupillary reflex)
80
Where is the suprachiasmatic nucleus?
hypothalamic nucleus just above the optic chiasm
81
What is the pathway of the circadian rhythm stimuli?
ipRGCs-->SCN -->paraventricular hypothalamic nuclei --> (1)sympathetic IML and (2) parasympathetic DMV (vagus) systems and (3)pituitary hormone release
82
where and how is melatonin released?
SCN regulated the pineal gland to release melatonin (symathetic nervous system stimulus)
83
What is melatonin/what does it do?
regulates sleep/wake cycles, temperature and cortisol release. it's released with decreased blue light, a sleep promoting factor
84
What is the pathway of the consensual pupillary response?
light --> melanopsin ganglion cells -->pretectal nucleus --> E-W nucleus -->ciliary ganglion --> spincter pupillae m.
85
What kind of nuclei are the erdinger-westphal nuclei? (parasympathetic or sympathetic?
parasympathetic
86
How does sympathetic activity affect the pupil size?
increases pupil size
87
What is the pathway for sympathetic activity in increasing light entry into the eye?
preganglionic T1-T2 --> superior cervical ganglion -->dilator pupillae and tarsal m.
88
How is sympathetic control of the iris and upper eyelid controlled?
local reflexes and limbic/hypothalamic emotional signals
89
What is the tarsal muscle? how is it innervated?
deep to levator palpebrae, attaches to the tarsal plate of the eyelid. opens the eye in response to sympathetic and emotional states.
90
What is ptosis? when is it seens and what is it caused by?
drooping of the eyelid caused by damage to the sympathetic nervous system. seen in Horners syndrome.
