weeks 4-6 Flashcards
visible human spectrum of light?
400-750nm
colour in retina?
3 cones, red green and blue.
red - 560
green - 530
blue - 430
combination of red:green discrimination and blue:yellow.
diagrams centre on off thingy
slides.
blue:yellow colour?
excited by blue in centre, inhibited by yellow in centre.
blue connected to ON bipolar
red/green connected to OFF bipolar
colour opponent ON and OFF bipolars.
red:green response?
high response to red, low response to green.
colour opponent centre surround
what wavelength of light does retinaldehyde absorb?
around 380 peak, UV range.
how can retinaldehyde absorb visible light then?
when bound to opsin, its function shifts to a different part of the spectrum.
when bound to rhodopsin where does retinaldehyde absorb light?
500 peak.
describe red/green colour blindness.
RG ganglion cells are on x chromosomes, only one copy in males.
can lack this if fucked up.
can still differentiate between blue/yellow
how do species differ?
number of cone classes
spectral sensitivity
why may species differences in colour vision occur?
ie telious fish, live at surface of water, they have >4 cone opsin genes.
look at deep sea species, only have 1 or 2 blue sensitive pigments. water filters out light at different wavelengths.
how did primates re evolve a 3rd cone opsin gene?
slides.
only females.
2 different x chr colours, can get 2 different ones by chance.
duplication of green on x chr for old world primates.
basic visual system pathways?
passes through lateral geniculate nucleus, to reach the primary visual cortex
basic CNS anatomy?
optic nerve from eye to optic chiasm, up to part of the thalamus (LGN) which projects to V1.
10% projects to other places.
what is the thalamus?
The thalamus is part of the brain which connects the midbrain (and therefore the periphery – the outside world) to the twinned cerebral hemispheres.
Essential link in transfer of sensory information to cerebral cortices
Originally thought of as “passive gateway”, isn’t since it can be selective.
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 or not sensory information should reach conscious awareness and is involved with sleep/wake and attention.
what is the main visual component of the thalamus?
dorsal lateral geniculate nucleus.
dLGN
what surrounds the thalamus?
thalamic reticular nucleus
job of the thalamus?
Sends information to cerebral cortex for all sensory systems except olfaction (communicates with the entire neocortex).
Every relay nucleus receives information back from cortex
Amount of feedback from cortex may equal or exceed amount of input from peripheral sense organs.
Feedback may be specific or diffuse and may separately target relay cells (cells projecting to the cortex) and inhibitory interneurons.
describe the structure of the LGN.
nissl stained.
6 layers.
1 ventral side, 6 dorsal side.
1 and 2 magnocellular layers (large cells)
3 to 6 parvocellular (small cells)
Each layer contains both excitatory (aka relay or projection) cells and (intrinsic) inhibitory interneurons
Very small cells between the laminae (koniocellular, or interlaminar), also excitatory relay cells.
Fovea/parafovea has a larger representation than peripheral retina (~half of the mass of the LGN) – aka the magnification factor
what does a nissl stain do?
look at cell density
where do LGN cells recieve their retinal input from?
Each cell receives most of its retinal input from a single retinal ganglion cell
describe projection onto the LGN.
Projection is orderly, each LGN having a representation of the opposite side of retinotopic space, the contralateral half of the visual field.
switches at optic chiasm.
as you move across the layers you move across visual space.
contralateral and ipsolateral?
contralateral opposite side.
ipsolateral same side
describe input to each layer oft he LGN.
each layer receives retinal input from only one eye.
There are therefore multiple representations of the same “retinotopic” space in each dLGN.
1 contra 2 ipsi 3 ipsi 4 contra 5 ipsi 6 contra
what is a receptive field?
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.
Receptive fields have been identified for neurons of the auditory system, the somatosensory system, and the visual system.
what is spatial frequency?
high = more detail.
low - larger receptive field. like pixels.
where is spatial frequency the highest?
fovea
describe parvocellular cells.
Dorsal 4 layers have smaller cell bodies
Input from retinal P ganglion cells
Receptive fields are concentric centre/surround organised, like the retina
Both On and Off centre subtypes
Chromatic, selective to colour (but can respond to brightness)
Small receptive fields
Higher preferred spatial frequency (cycles/degree)
Lower preferred temporal frequency (cycles/sec)
what is temporal frequency?
movement.
describe magnocellular cells
Ventral 2 layers, have larger cell bodies,
Input from retinal M ganglion cells
Receptive fields are concentric centre/surround organised, like the retina
Both On and Off centre subtypes
Achromatic, look for brightness. not rod vision.
Larger receptive fields (but note eccentricity effect)
Lower preferred spatial frequency (cycles/degree)
Higher preferred temporal frequency (cycles/sec)
what are koniocellular (k/i) cells?
Newest addition to the family
Very small cells found between main laminae
Direct input from blue/yellow RGC’s
Indirect input from SoveriaColiculus!
Heterogenous types?
Functional properties/function largely unknown
how often do you use rods?
very rarely, even streetlights keep cones going.
describe relay cells
~90% of LGN cells are relay, single axon projects to V1
Each has an axon collateral which sprouts just above the LGN – terminates in the visual sector of the thalamic reticular nucleus (TRN) known as the perigeniculate nucleus (PGN)
Also use glutamate (or perhaps aspartate) as their neurotransmitter and are therefore excitatory
describe inhibitory cells.
All use Gamma-aminobutyric acid (GABA) as neurotransmitter
Two populations:
intrinsic to the LGN, project locally (possibly using dendro-dendritic communication) and receive retinal input
feed-forward inhibition
input from retinal ganglion cells, turn into inhibitory message and pass on to relay cells.
within the perigeniculate nucleus (PGN), project widely within PGN, and back into LGN
feed-back inhibition
copy of message from relay cells, sends to cortex, comes back to LGN to feedback to cells which provided the excitatory message originally.
describe modulatory systems.
Long projections systems, initially classified by the neurotransmitter and position in the brainstem
– a family that includes adrenaline, noradrenaline and dopamine! (amongst others…)
describe the locus coeruleus (A6)
In the brainstem (pons) gray matter ~ 10,000 cells/side
Maintains vigilance, responsiveness to the unexpected
Extensive projections to the thalamus, cortex and cerebellum
Also projects within brainstem and spinal cord:
parkinsons?
damages thalamic cells, dopamine.
serotonin?
Serotonergic (tryptaminergic) cells found in the Raphe n. (Fr. Raphé = seam)
Pons and midbrain groups project the whole of the forebrain
Role in hypothalamic cardiovascular control, thermoregulation and modulate thalamic and cortical function:
ACh?
Cholinergic neurons in the upper pontine tegmentum (tegmentum = “covering”) and basal forebrain diffusely innervate much of brain stem and forebrain.
Basal forebrain groups: innervates entire cerebral cortex including amygdala and hippocampus
Pontine groups: innervate brainstem reticular formation and thalamus
alzheimers where?
basal forebrain groups ACh, not pontine groups.
names for primary cortex?
area 17, striate cortex, V1
describe the structure of the primary cortex.
6 layer structure.
some sub lamination particularly in layer 4.
golgi staining?
stains unique cells, not sure why those are chosen.
allows to see internal organisation of something, suggests circuit when done on cortex.
types of cells in the cortex?
pyramidal cell
spiny stellate cell, looks like a star.
spiny/non spiny:
spiny - glu
non spiny - GABA are minority, below 20%
advantage of spiny dendrites?
increase surface area for synaptic contact/inputs.
excitatory v inhibitory cortical cells
table in lecture.
describe layers in the primary cortex.
1,2,3 are supragranular (above granular layer)
5,6 are infragranular (below granular cell layer).
Layer 1 – small no of cells, all GABA, no idea what it does.
Layer 2/3 gradation not a straight line.
L2 external granule layer with small spherical cells.
L3 more pyramidal cells, external pyramidal layer.
Layer 4 – stellate cells, mostly spherical cells. granule cell layer.
Layer 5 – the internal pyramidal cell layer, cells biggest out of layers.
Layer 6 – heterogeneous mix; polymorphic or multiform layer, “blends” into white matter
inputs to visual cortex? v complicated
draw out be easier.
describe ocular dominance columns.
Axons from the laminated LGN go to separate “zones” in the cortex, forming “ocular dominance columns”.
Ocular dominance columns – equal space devoted to each eye, each about 500µm in width – form a “zebra-like” pattern across the cortical surface.
describe simple cells.
orientation preference and seperate ON/OFF cells.
describe a complex cell
add simple cells with similar orientation, receptive field now has overlapping ON/OFF responses.
hypercomplex cells?
length tuned too.
one short excitatory input, one long inhibitory input.
like a stretched LGN field.
simple vs comples cells.
graph
