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sensory systems > basic visual pathway > Flashcards

basic visual pathway Flashcards

1
Q

thalamus

A
  • Large structure
  • Divided into multiple nuclei with distinct functions
    -some visual
    -some non-visual
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2
Q

lateral geniculate nucleus

A
  • Primary visual part of the thalamus
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3
Q

what projects to teh LGN in a primate?

A

~90% of retinal ganglion cells

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4
Q

role of teh thalamus

A
  • Plays a major gating/ modulatory role in the relay of sensory information
  • Integrates information from cerebellum and basal ganglia, sending this information to the motor regions of cortex
  • Determines whether information should reach consciousness awareness and is involved with sleep/ wake and attention
    -determines whether we ‘notice’ specific pieces of sensory information
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5
Q

thalamic organisation

A
  • The main visual component of the thalamus is the LGN
  • Other region of processing are:
    -Pulvinar (communicates to higher visual cortex)
    -thalamic reticular nucleus
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6
Q

general thalamic properties

A
  • Send information to cerebral cortex for all sensory systems except olfaction
    -individual sub-nuclei that process specific senses
    -overall communicates with the entire cortex
  • Every relay nucleus receives information back from the cortex
  • Amount of feedback from cortex may equal or exceed that from sense organs
  • Feedback may be specific or diffuse, may separately target relay cells and interneurons
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7
Q

what type of structure is the LGN?

A

laminated

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8
Q

how many layers of laminae in the LGN?

A

6 layers

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9
Q

which layers are magnocellular?

A

1 and 2

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10
Q

which layers are parvocellular

A

3,5,6

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11
Q

what stain shows up cell bodies in the LGN?

A

nissl stain

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12
Q

large cells

A

magnocells

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13
Q

small cells

A

parvocells

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14
Q

what does each cell in the LGN receive most of its input from?

A

a single retinal ganglion cell

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15
Q

what does each LGN layer contain?

A

excitatory (relay) cells and local inhibitory interneurons

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16
Q

what is underneath each laminae?

A

very small excitatory relay cells: koniocellular layers

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17
Q

how are retinal projections ordered?

A

retinotopically

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18
Q

where does each LGN get its signals from?

A

RGCs viewing the opposite visual hemifield

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19
Q

what do adjacent cells within each LGN layer view?

A

adjacent portions of visual space

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20
Q

what representation does the foveal region have in the LGN

A

a disproportionately large representation: half the mass of the LGN

21
Q

how many eyes does each layer of the LGN receive input from?

A

one

22
Q

what is the effect of each laminae only receiving input from one eye?

A

there are multiple representations of the same ‘retinotopic’ space in each LGN

23
Q

cells along the projection line all view…

A

overlapping region of visual space

24
Q

what is the receptive field of a sensory neuron

A

a region of space in which the presence of a stimulus will alter the firing of that neuron

25
Q

what organisation of receptive field to LGN cells have?

A

concentric centre-surround antagonistic

26
Q

what do LGN centre surround receptive fields act as?

A

local edge detectors

27
Q

spatial acuity small receptive field

A

high spatial acuity: more detail

28
Q

spatial acuity large receptive field

A

low spatial acuity: less detail

29
Q

temporal frequency of RFs that respond best to slow stimuli

A

low preferred temporal frequency

30
Q

temporal frequency of RFs that respond best to fast stimuli

A

high preferred temporal frequency

31
Q

parvocellular LGN neurons (8 points)

A
  • Dorsal 4 layers have smaller cell bodies
  • Small receptive fields
  • High spatial acuity (can resolve fine detail)
  • Prefer low temporal frequencies (slow changes)
  • Receptive fields have concentric centre/surround like the retina
  • Both On and Off centre subtypes
  • Chromatic (red/green) but can respond to brightness
  • Input from retinal P ganglion cells
32
Q

magnocellular LGN neurons (8 points)

A
  • Ventral 2 layers
  • Have larger cell bodies
  • Lower spatial acuity (can’t resolve fine detail)
  • Prefer high temporal frequencies (fast changes)
  • Receptive fields have concentric centre surround like the retina
  • Both On and Off-centre subtypes
  • Achromatic
  • Input from retinal M ganglion cells
33
Q

koniocellular LGN neurons (5 point)

A
  • Very small cells found between laminae
  • Direct input from blue/yellow RGC’s
  • Indirect input from superior colliculus
  • Heterogenous types?
  • Functional properties/ function largely unknown
34
Q

organisation within laminae

A

eccentricity

35
Q

what is magnified with LGN retinotopic map?

A

fovea

36
Q

what changes with eccentricity

A

receptive field size/ proportion of M and P cells

37
Q

relay cells (4 points)

A
  • ~90% of LGN cells are relay, single axon projections to V1
  • Use glutamate- therefore are excitatory
  • Each has an axon contralateral just above the LGN
38
Q

where does the contralateral axon to each relay cell (just above the LGN) terminate?

A

in the visual sector TRN, known as the perigeniculate nucleus (PGN)

39
Q

what neurotransmitter do all inhibitory cells use?

A

gamma-aminobutyric acid (GABA) as a neurotransmitter

40
Q

what are the two populations of inhibitory neurons

A

feed forward inhibition and feedback inhibition

41
Q

feed forward inhibition neurons

A

modulates centre:surround inhibition
intrinsic to the LGN
receives retinal input
project locally

42
Q

feedback inhibition neurons

A

global changes in the LGN cell responses
with the perigeniculate nucleus
project widely within the PGN
feedback to LGN

43
Q

where does the LGN send excitatory input to?

A

V1

44
Q

modulatory systems

A

long projection systems from the brainstem and basal forebrain that adjust thalamic function

45
Q

noradrenaline

A
  • Produced in locus coeruleus (LC):
    -small periaqueductal gray matter cell group ~10,000 cells/side
  • Maintains vigilance, fight or flight responses
  • Extensive projections incl. thalamus and cortex
  • Modulates visual sensitivity
46
Q

acetylcholine

A
  • Basal forebrain groups: innervates entire cerebral cortex including amygdala and hippocampus
  • Pontine groups: innervate brainstem reticular formation and thalamus
    important for arousal and REM sleep
47
Q

serotonin

A
  • Serotonergic cells found in the Raphe nuclei
  • Pons and midbrain groups project the whole of the forebrain
  • Role in mood, cardiovascular control, thermoregulation + modulate thalamic and cortical function
  • Specific function largely unknown
48
Q

dopamine

A
  • Multiple cell groups, some of which provide input to thalamus
    not those with Parkinson’s
  • Roles in reward, neuroendocrine, motor control
  • Thalamic projections mainly avoid primary sensory areas
  • Dopaminergic modulation of the thalamus

sensory systems (17 decks)

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