1
Q
ipsa-lateral
A
same side
2
Q
contra-lateral
A
opposite side
3
Q
Thalamus - what is it
A
- large structure
- most sensory signals pass through thalamus
- divided into multiple nuclei with distinct functions
- visual and non-visual
4
Q
Lateral geniculate
A
- primary visual part of thalamus
- majority of RGCs (~90%) project here in primates
5
Q
what are some other places RGCs send axons
A
- pretectum (pupil size)
- superior colliculus (eye, head movement)
6
Q
thalamus - what is it part of
A
- part of diencephalon - connects mid brain to cerebral hemispheres
7
Q
thalamus - what does it do
A
- receives information from periphery
- process & communicates to cortex
- essential link in transfer of sensory information
8
Q
thalamus - major role
A
- gating/ modulatory role in relay of sensory information
- off during sleep/ on during wake
9
Q
the thalamus + non-sensory information
A
- integrates information from cerebellum and basal ganglia, sending this information to the motor regions of cortex
10
Q
thalamus + attention
A
- determines whether or not information should reach conscious awareness and is involved with sleep/wake and attention
- determines whether we ‘notice’ specific bits of information
11
Q
thalamic organisation (main components)
A
- ventrolateral nuclei
- medial geniculate nucleus
- lateral geniculate nucleus
- pulvinar
- reticular nucleus
12
Q
ventrolateral nuclei
A
- process somatosensory information (touch)
13
Q
medial geniculate nucleus
A
- auditory signals
14
Q
lateral geniculate nucleus
A
- main visual component of thalamus
15
Q
pulvinar
A
communicates to higher visual cortex
16
Q
thalamic reticular nucleus
A
- switching thalamus on/off
17
Q
general thalamic properties
A
- send information to cerebral cortex for all sensory systems except olfaction
- every relay nucleus receives information back from cortex (two way)
18
Q
thalamic sensory properties
A
- indivudal sub-nuclei that process specific senses
- overall communicates with entire cortex
19
Q
thalamic properties - feedback
A
- 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.
20
Q
LGN structure
A
laminated
- 6 layers /laminae
- nissl staining
21
Q
laminae 1 and 2
A
magnocellular
- larger / more granular cells when stained
22
Q
laminae 3 to 6
A
parvocellular
- small cells
23
Q
two types of cells in laminae
A
- relay
- local inhibitory neurons
24
Q
relay cells
A
excitatory glutametergic neurons
- axons from LGN to V1 (primary visual cortex)
25
each LGN cell
- receives input from a single retinal ganglion cell
26
organisation of LGN layers
27
what cells are under each laminae
small excitatory relay cells
- (white regions when stained)
- koniocellular layers/neurons
28
LGN layers and retinal projections
- retinotopically ordered
- LGN gets signals from RGCs viewing the opposite visual hemifield
- within each LGN layer adjacent cells view adjacent portions of visual space
29
foveal representation in LGN
- foveal region has disproportionately large representation ~half the mass of the LGN
30
layers + retinal input
- each layer receives retinal input from only one eye
- darker layers (contra input)
- lighter layers (ipsi input)
31
projection line
cells along the projection line all view overlapping regions of visual space
32
receptive fields
the receptive field of a sensory neuron is a region of space in which the presence of a stimulus will alter the firing of that neuron
33
LGN cells + RGCs similarity
centre:surround organisation
34
small receptive field - LGN
- high spatial acuity
- more detail
35
large receptive field - LGN
- low spatial acuity
- less detail
36
low preferred temporal acuity
respond best to slow
37
high preferred temporal acuity
respond best to fast
38
parvocellular LGN neurons
- dorsal 4 layers
- small cell bodies
... small receptive fields
... high spatial acuity
...lower temporal frequencies
- centre:surround ON or OFF
- chromatic so can detect red/green colour
- respond to brightness
- input from retinal P ganglion cells
39
magnocellular LGN neurons
- ventral 2 layers
- large cell bodies
... large receptive fields
... low spatial acuity
... high temporal acuity
- centre:surround ON or OFF
- achromatic
- input from retinal M ganglion cells
40
Koniocellular LGN neurons
- very small
- between main laminae
- direct input from blue/yellow RGCs
- indirect input from superior colliculus
- heterogenous?
- function largely unkown
41
relay cells in LGN
- each axon has a collateral just above LGN
.. terminates in the visual sector of the TRN known as the PGN (perigeniculate nucleus) where it contacts inhibitory interneurons
42
inhibitory cells
- all use GABA as neurotransmitter
- LGN or PGN population
- modulate centre:surround properties of neuron
43
LGN inhibitory cells
- intrinsic to LGN
- receive retinal input, project locally
- feed-forward inhibition
- local switch off
44
PGN inhibitory cells
- project widely to PGN, and back into LGN
- feed-bacl inhibition
- global (switch off) changes in LGN cell responses
- critical in sleep and shutting off thalamus
45
modulatory systems
long projection systems from the brainstem and basal forebrain that adjust thalamic function
e.g. adrenaline, noradrenaline, serotonin, acetylcholine, dopamine
46
noradrenaline
- produced in locus coeruleus (LC)
- vigilance, fight or flight responses
- projections incl. thalamus + cortex etc.
- modulates visual sensitivity
47
Locus Coeruleus
- small periaqueductal gray matter cell group
48
Acetylcholine
- basal forebrain groups
- pontine groups
49
basal forebrain acetylcholine groups
innervates entire cerebral cortex including amygdala and hippocampus
50
pontine groups
innervate brainstem reticular formation and thalamus
- important for arousal and REM sleep in the thalamus
51
serotonin - 5-HT
- serotonergic cells found in Raphe nuclei
- Pons and midbrain groups projects the whole of the forebrain
- role in mood, cardiovascular control, thermoregulation + modulate thalamic and cortical function
52
dopamine
- many cell groups, some input to thalamus
- roles in reward, neuroendocrine, motor control
- thalamic projections mainly avoid primary sensory areas
BIOL21341/ Sensory Systems
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