Vision 2 Flashcards
Example of a disease that affects the laminate cribosa
Glaucoma
Optic nerve structures
ONH=Optic nerve head=Blind spot
N= Ganglion nerve fibres
S= sclera
L= Lamina cribosa
How far from back of eye to optic chasm?
5cm
*** you might need to watch some videos on this or smth because I’m confused
Axons from which cells travel in hthe optic tract?
Retinal ganglion cells
Where is the first synapse in the visual pathway?
Lateral geniculate nucleus (LGN) of the thalamus
LGN - parvocellular layers
Neurones have smaller bodies
Respond to colour, finer details, still jets, slow moving objects
LGN - Magnocellular layers
Neurones have larger cell bodies
Respond to objects in motion
Visual context columnar organisation
Visual cortex is highly organised. Ocular dominance and orientation cortical columns are related. These relationships depend on normal visual and oculomotor experience during development
Amblyopia (“lazy eye”)
Input from one eye dominates cortex
Abnormal cortical development
Function of other eye reduced
Receptive Fields (RF)
Area of retina that affects firing rate of a given neuron in the circuit
Receptive fields are determined by monitoring single cell responses
Stimulus is presented to retina and response of cells is measured by an electrode
Remember centre-surround receptive fields
Ganglion cells
~20 types in mammalian retina, different functions
Thalamo-cortical pathway – classic centre/surround rf structure
Central GCs- small rfs, basis of high acuity vision; wavelength sensitivity, basis of colour vision
Ganglion cells - P-type
Smaller cell bodies/dendritic fields; small, central, receptive fields; sustained (tonic) responses; wavelength sensitive.
Project to P layers of LGN
Ganglion cells - m-type
Larger cell bodies/dendritic fields; larger receptive fields; transient (phasotonic) responses; wavelength insensitive.
Project to M layers of LGN
Primary Visual Cortex
The left visual field projects onto the right occipital lobe & vice versa
The central part of the visual field is represented posteriorly
The peripheral visual field is represented more anteriorly
The superior visual field is represented ventrally
Layers of the Primary Visual Cortex
6 layers
Principal layer for inputs from LGN is layer 4:
4A - minor inputs from parvocellular layers
4Cα - from magnocellular layers
4Cβ - from parvocellular layers
DF
Irreversible brain damage from hypoxia as a result of CO poisoning
Visual form agnosia –
Could not indicate the size, shape, orientation of objects; could not draw “live” pictures of objects.
But – visually guided reaching and grasping not impaired
