Visual System Flashcards
where does the pathways subserving visual perception originate?
retina
where does the pathway of vision go from retina?
retina –> dorsal nucleus of lateral geniculate body of thalamus –> primary visual cortex (striate cortex, area 17, V1)
then to occipital, temporal and parietal association areas
where do the retinal ganglion cell axons pass via?
optic nerves, optic chiasma and optic tract
how many axons does the optic nerves have?
1 million myelinated axons
describe the optic chiasm
–Partial crossing of optic nerve fibres
-ganglion cell axons from nasal retina cross here
–Essential for binocular vision
describe the optic tract
–Curves around the rostral midbrain and ends in the lateral geniculate body of the thalamus
what is binocular and monocular crescents field?
binocular –>visual field viewed by both eyes
monocular crescents –> visual field viewed by only one eye
where does the left hemifield project to in the brain? and vice versa
left hemifield to right side of the brain –> the right LGN and right visual cortex (right hemifield to left side of brain
describe the upper half of the visual field (which fall on the bottom parts of the retina)
– processed by lateral LGN and visual cortex below the calcarine sulcus
describe the lower half of the visual field (which fall on the top parts of the retina)
– processed by medial LGN and visual cortex above the calcarine sulcus
describe the macula (colour, information of high acuity)
– processed by posterior LGN and
posterior 1/3 of visual cortex
describe the lateral geniculate body
-The lateral geniculate body is a small swelling beneath the posterior projection of the pulvinar of the thalamus
- Fibres of the optic tract terminate in the dorsal nucleus
-Receptive fields of LGN neurons: almost identical to the ganglion cells that feed them
-At the level of the lateral geniculate body the information from the two eye are kept separate
how many layers does the LGN have and describe the magnocellular LGN neurons, parvocellular LGN cells and nonM-nonp cells
-6 distinct layers
-Magnocellular LGN neurons: large centre-surround receptive fields with transient response –> layers 3-6 and these layers innervated by P-type retina cells
-Parvocellular LGN cells: small centre-surround receptive fields with sustained response –> layers 1, 2 and these layers innervated by M-type retina cells
-nonM-nonP retina cells project to K1-K6 (areas between layers) to the Koniocellular LGN layer
what layers for crossed and uncorssed fibres end in the LGN
-Crossed fibres end in layers 1, 4, &6
- Uncrossed fibres end in layers 2, 3, &5
what does the visual cortex (aka striate cortex) occupy?
-primary visual cortex occupies the upper and lower lips of the calcarine sulcus of the medial occipital lobe (area 17)
describe the geniculocalcarine tract
from the LGN to the V1 via this tract
how many layers of the striate cortex
-6, I - VI
-IV –> broken up into IVA, IVB, IVC (alpha and beta)
what is contained in layer IVC in V1?
spiny stellate cells (spine-covered dendrites)
What layers are the pyramidal cells (spines and thick apical dendrites) contained in V1?
layers III, IVB, V, VI
What layers are the inhibitory neurons (lack spines) in the V1?
all layers, form local connections
Where do magnocellular LGN neurons project to in the V1?
layer IVC-alpha
Where do parvocellular LGN neurons project to in the V1?
layer IVC-beta
Where do Koniocellular LGN neurons project to in the V1?
-Koniocellular LGN axons make synapses primarily in layers I and III
-direct projections from koniocellular layers of LGN to blobs in layer II/III
What are the patterns of intracortical connections in the V1
-Connections within the cortex are vertically organised
-preserves retinotopic mapping of layer IV through different cortical layers - hence cortical “columns”.
thought to be basis of information processing in cortex
- there are also lateral connections in layers III and V that may be involved in processing across the cortex e.g. for “perceptual binding
