Primary visual (v1) cortex: location & organisation Flashcards
what does the v1 area of brain allow for us to have
conscious visual perception
where is the primary visual cortex located in relation to the primary visual pathway
the apex
list the steps of the primary visual pathway
- retinal ganglion cells
- optic nerve, chiasm, tract
- lateral geniculate nucleus
- optic radiations
- primary v1 cortex
what do the neurons of the LGN travel out of in the primary visual pathway
optic radiations
what do the optic radiations make neural connection with
the primary visual area in the occipital lobe
where is the occipital lobe located within the cerebral cortex
the back end
how many layers of cells does the primary visual v1 cortex consist of
6
which layer in the primary visual cortex has subdivisions
layer 4
what are the names of the subdivisions of layer 4 called
- 4a
- 4b
- 4c alpha
- 4c beta
which of the layers is wide
layer 4
why is layer 4 in the primary visual cortex particularly wide
due to its 3 major subdivisions
in which orientation are the intra-cortical connections of the primary visual cortex
vertical/columnar
where is the primary visual v1 cortex located in the occipital lobe
mainly medial, upper & lower banks of the calcimine sulcus in each hemisphere
what is the primary visual v1 cortex also known as
- area 17
- striate cortex
which visual hemifield does the primary visual v1 cortex represent
opposite
what does unilateral damage of the primary visual v1 cortex cause
hemianopia
loss of vision or blind in opposite half of visual field
give an example of the outcome of unilateral damage of the primary visual v1 cortex
left v1 damaged = right hemianopia
which two lobes does the calcarine sulcus divide
parietal lobe from the occipital lobe
at what angle is the calcimine sulcus to the parieto-occipital sulcus
90 degrees
which matter is the calcarine sulcus found above & below the primary visual area
grey matter
describe the structure of the calcarine sulcus
it is not a slit, but more like a U-bend with cortical tissue in its depth (is a continuous structure) called a fundus
what is a cyto-architecture referred to of a particular region
its cellular organisation
list the cellular organisation of brodmann area 17 that is in common with all other areas of the cerebral cortex
- has 6 separate layers of cells in the gray matter (few in layer 1)
- small granule or stellate (star shape) cells concentrated in layer 4
- receives direct input from the thalamus (LGN) & has direct communication with pyramidal cells in the layer directly above and below to continue processing of the visual image
list the cellular organisation of brodmann area 17 that is unique which is found nowhere else in the cerebral cortex
- layer 4 is very wide (1/3 of cortical thickness) & has 3 separate sub-layers (A, B, C)
- with sublayers 4a & 4b containing pyramidal and not granule cells
- layer 4c with granule cells having separate upper (alpha) and lower (beta) sub-layers
- layer 4b contains a band or stripe of myelinated axons
what is the name of the band/stripe of myelinated axons located in layer 4b
the stria of gennari
what do sub-layers 4a and 4b not contain
granule cells
what do sub-layers 4a and 4b only contain
pyramidal cells
out of the 6 layers within the grey matter, which layer does not contain cell bodies of cortical neurons
layer one
which layers out of the 6 in the primary visual cortex contains cell bodies of cortical neurons
2-6
what does layer 1 out of the 6 contain in the primary visual cortex
dendrite & axons synaptic connections
which surface is layer 1 found just below of
pial surface
how intense is layer 1 of the v1 cortex and why
pale
due to no neurons or cell bodies found within this layer
which layer has the deepest intensity under the microscope and why
layer 4c
due to highest density of neurons and cell bodies and stellate cells
what does layer 4c alpha and 4c beta receive input from
LGN
in which layers does layer 4c alpha and 4c beta connect to cells of
layers above 2-4b
&
below 5-6
how wide and tall is the grey matter of the cerebral cortex
2mm x 2mm
what do stellate cells form in layer 4c
small ‘local circuit’ neurons, which relay information they receive from the LGN via short axons to pyramidal cells in the layers just above or below them
how short are the dendrites of stellate cells in layer 4c
no longer than layer 4c
which orientation do the axons of stellate cells in layer 4c travel
vertically (axons go up & down)
what do the vertical axons of stellate cells in layer 4c connect to
pyramidal cells
what sort of dendrites do pyramidal cells have and which direction do they go
fat vertical
going up
what sort of circuit do pyramidal cell neurons have
not a local circuit neuron but is large projection neurons
where do the axons of pyramidal cells do
they do not stay in v1 but will go to different locations/distant targets via long axons
how are the local cortical circuits organised
mainly in vertical columns
why are the local circuits organised in vertical columns
because granule cell axons run mainly vertically across the layers to make excitatory synapses on the prominent vertically-oriented (primary) dendrites & dendritic spines of all pyramidal cells
which input to granule/stellate cells in layer 4c receive
LGN
what do pyramidal cells in layers 2-4b connect to
other nearby extra striate (beyond striate cortex) areas of visual association cortex which are other areas of the cerebral cortex
what sort of connections do pyramidal cells below layer 4c have
descending sub cortical connections eg layer 5 not to the LGN but to the superior colliculus (which is lower down) and layer 6 supplies excitatory connections back to the LGN which supplies the input
what do pyramidal and granule/stellate cells use as their neurotransmitter
glutamate
which v1 cortical cells are inhibitory
basket cells
&
chandelier cells
what are the neurotransmitters of the inhibitory cells of the v1 cortical cells
GABA
what are the inhibitory cells of the v1 cortical cells involved with
lateral GABA-ergic inhibitory processes that also influences the RF properties of nearby pyramidal cells
which brodmann area is found on the upper bank of the medial calcarine sulcus
18
which brodmann area is found on the lower bank of the medial calcarine sulcus
18
which brodmann area is the myelinated stria only found in
17
which brodmann area is the calcarine sulcus fundus
17
what is the U bend
where the grey matter is continuous
what is the name of the U bend of grey matter
fundus of calcarine sulcus
what does the striate cortex only found in v1 area 17 contain
has a continuous band of myelinated axons (white matter) running in grey matter of the calcarine sulcus
what layers does the stria of gennari straddle along
4c alpha & 4b
list the chemical organisation of area v1 that is in common with all other areas in the cerebral cortex
- neurons in all cell layers of v1 have mitochondria
- which contain the metabolic enzyme cytochrome oxidase (CO) (& found in all mitochondria of body & all neurons of body have this)
- can be visualised with special staining techniques
list the properties of the pattern of cytochrome oxidase activity which is found nowhere else in the cortex apart from v1
- columns of intensely CO stained cells in layers 2-4b & weaker in layers 5-6
- apporox 0.25mm wide
- separated by columns of less CO stained cells in these layers of width
- view horizontally across the layers, the CO-rich cells form a regular polka dot arrangement across whole of v1
- with polka dot to dot centre spacing of ~0.5mm
what is the name of the cytochrome rich cells
the cytochrome oxidase blobs
what is the name of the cytochrome poor cells
the inter blob cells which contains less cytochrome oxidase
which layer is uniformly cytochrome oxidase rich
4c
where are there columns rich of cytochrome oxidase
above and below layer 4c
when viewing layer 3 of primary v1 cortex under a microscope, what do the dark dots represent
blobs
when viewing layer 3 of primary v1 cortex under a microscope, what do the lighter patches represent
interblobs (surrounded by blobs)
when viewing layer 3 of primary v1 cortex under a microscope, what do the holes represent
blood vessels
what are the neurons in the blobs
colour selective (interested in chromatic sensitivity placed in their RFs)
what are the neurons in the inter blobs
contour selective (interested in responding to different lines and edges/form processing)
what property do inter blobs have
orientation selectivity
list the series of connections which start by the midget ganglion cells of the retina
- midget ganglion cell axons connect to the parvo cellular layer 3-6 of the LGN
- which go through the parvo cell pathway & make connections with the 4c beta granule cells
- which provide inputs for
1. blob cells (involved in red green colour processing)
2. inter blob cells (involved in form processing)
list the series of connections which start by the parasol/magno ganglion cells of the retina
- parasol ganglion cell axons connect to the mango cellular layer 1 & 2 of the LGN
- which go through the magno cell pathway & make connections with the 4c alpha granule cells
- which provide inputs for
1. inter blob cells (involved in form processing)
2. layer 4b (contours and direction in space)
list the series of connections which start by the small bi-stratified ganglion cells of the retina
- small bi-stratified cell axons connect to the koniocellular layers of the LGN
- which go through the konio cell pathway & provide direct inputs for the blob cells (involved wavelength selective blue yellow processing which is different to other blobs)
what is the properties of contours & direction in space where a contour is moving in layer 4b called
direction selectivity
what is direction selectivity of layer 4b involved in
motion pathway
why do 4c alpha granule cells also make connections with inter blob cells as well as 4c beta cells
to contribute to form processing
