Lecture 26 Flashcards
the major retinal projection to the brain is the ____ pathway
retinogeniculostriate pathway
where is the the striate cortex
very back of the brain
occipital lobe
where does the visual signals from each eye split
optic chism
how many LGN layers
6
LGN receives info from
retina
LGN is major relay site in the
thalamus
what happens in LGN when sleeping
inhibition of inhibitory neurons
parvocellular layer
small cell bodies
magnocellular layer
large cell bodies
koniocellular layer
very small cell bodies
visual signal in LGN organized in ))))))
retinotopic maner
retinoyopic organization
each layer on LGN receives info from 1 eye
maps complete half of the visual field
objects in right visual field activates all 6 layers of left LGN
M ganglion cells
project from retina to magnocellular layer
for large, fast moving objects
P ganglion cells
project from retina to parvocellular layer
for details of stationary objects
retinal ganglions project to 3 other subcortical structeres …
- superior colliculus
- Pretectum and Edinger-Westphal nucleus
- Suprachiasmatic nucleus (SCN)
superior colliculus
- RGCs form a retinotopic map in the SC
- SC integrates visual, auditory and somatosensory inputs and sends motor outputs to motor areas of the brainstem
- Controls saccades, rapid eye movements that orient fovea
Pretectum and Edinger-Westphal nucleus
- Iris control: in too bright light/dim light conditions, send motor output back to eye via cranial nerve III to adjust pupil diameter
- Lens control: if image is out of focus, send motor output to ciliary muscle -> changes accommodation
Suprachiasmatic nucleus (SCN)
- A special group of retinal ganglion cells is photosensitive (responds to ambient light levels)
- Project to SCN, which serves as the circadian clock that derives circadian rhythms
- SCN projects to pineal gland which produces the hormone melatonin in high levels of darkness
how many layers of striate cortex
6
layers 2 and 3 of striate cortex
mainly coordinate info with other visual cortical areas
layer 4
thickest layer, 4A 4B 4C
most LGN fibers terminate in 4C
• Magnocellular axons project onto upper part of layer 4C
• Parvocellular axons project to lower part of layer 4C
layers 5 and 6
mainly communicate with sumcortical structures (LGN, SC)
Topographical mapping
adjacent regions of the visual fields are mapped onto adjacent areas in the V1
Cortical magnification
visual map is distorted on the visual cortex, cortical representation of the fovea is greatly magnified compared with the cortical representation of peripheral vision
is there a linear or non linear representation in V1
non linear
why does foveal region gets more space in the V1
normally most important info is normally in the centre of our vision, and the greater density of retinal ganglion cells in the fovea
Visual crowding in the periphery
Objects that can be easily identified in isolation but seem jumbled up when surrounded by other objects
where to inputs from 2 eyes intermingle (binocular)
neurons above and below 4C
what is the role of binocular neurons
to compare the image from each eyes which are slightly different, increase fine depth perception
orientation selectivity
receptive fields that are bars will respond most when light aligned perfectly with excitatory area
how are LN receptive fields made
LGN neurons feed into V1 neurons in a precise manned
directional sensitivity
neuron shows significantly greater firing to stimulus movement in a particular direction
colour contrast detection pathways ultimately lead to
blobs in V1
cells in parvocellular pathway provide info on what colours
red and green
cells in koniocellular pathway provide info on what colours
blue and yellow
