Visual pathways and lesions Flashcards
what is the LGN
lateral genticulate nucleus which is a relay center in the thalamus for the visual pathway
receives input from the retina
what is the optic radiation
a collection of axons from relay neurons in the lateral genticulate nucleus of the thalamus to the visual cortex aka striate cortex
what is perimetry
the measurement of visual field function
what is the result of a lesion of the left optic nerve
just the left border of the visual field is lost
what is the result of a lesion in the left optic tract
the whole right half of the visual field is lost
what is the effect of a lesion in the left temporal occipital area
the whole right half of the visual field is lost, as with the optic tract
what is the result of a lesion in the optic chiasm
the left and right borders of the vision will be lost due to the fact that all peripheral vision crosses over at the chiasm
bitemporal heteronymous hemianopsia
vision is missing in the outer half of both the right and left visual field.
caused by an optic chiasm lesion
what is the contralateral homonymous hemianopia
the two halves of the visual field on the same side are lost
caused by a lesion in the optic radiation or a lesion in the striate visual cortex
what is contralateral superior quadrantanopia
upper quarter of the visual field is lost on the same side
what state are cones and rods in in the dark
depolarised
what do depolarised rods and cones relesase
neurotransmitter
this is known as dark current
what is the neurotransmitter involved in vision
glutamate
can be excitatory or inhibitory to the bipolar cell
what are horizontal cells
connect multiple rods or cones to single or groups of bipolar cells
are horizontal and amacrine cells inhibitory or excitatory
inhibitory
what is the function of the lateral connections in amacrine and horizontal cells
lateral inhibition which sharpens contrast and provides edge detection
what is the role of ganglion cells
project information from the retina to the thalamus (LGN)
describe the information processing that goes on in the retina
information is condensed about light into a series of overlapping circles, in which a comparison is made between the brightness in the centre and the brightness in the periphery
what happens to information that leaves the optic tract and passes to the pretectal nuclei in the midbrain (10%)
used for eye movement towardsa novel stimulus for tracking
enables light on the retina to stimulate eye movements that put it over the fovea
what is the function of the LGN
detects and relays information on movement
Separates signals to derive depth
perception
Emphasises visual inputs from
cones
Sharpens contrast
Separates information from the
upper and lower visual field
decribe retinotropy
Cells in the LGN and subsequently in the
retina are mapped to the visual fields so that adjacent signals on the visual field are mapped to adjacent areas in the striate cortex
Like the sensory homunculus, certain
areas (macular) are magnified in
representation
describe how output from the LGN is modified or filtered
incoming information from the cerebral cortex, thalamic nuclei and brainstem reticular formation
where is the primary visual cortex
medial surface of the occipital lobe around the calcarine fissure, has a striped appearance
describe the histology of the striate cortex
multilayered with different layers performing different tasks
6 layers with 3 sublayers = 9 in total
what are the three main functions in the primary visual cortex
colour recognition
ocular dominance
orientation detection
what are blobs
columns of cells associated with colour recognition
can be stained with cytochrome oxidase
what are dominance strips
cells receiving information from one eye lie adjacent to those receiving corresponding information from the other eye
found in layer 4c
signals in the centre of a stripe are registered as dominant for that eye
what is stereopsis
perspective and the relative size of objects
what is the temporal lobe stream
the temporal lobe is involved in identifying what something is
where is the Where system located
parietal cortex- involved in object location and spatial relations
i can be possible to perceive an object but not know where/ what it is
what is integrative or object orientation agnosia
a temporal lobe lesion affects the ability to recognise objects from a variety of different perspectives and integrate multiple visual clues
category specificity e.g. face vs fruit
what are the funcitons of the Where system
- Navigation through the environment – a mapping of object around us
- Movement of eyes to locate and follow objects in our field of view
- Interpretation of motion and perspective in the World around
what is the retinotectal pathway
Pupillary light reflex
pretectal neurons project to ipsi- and contralateral EdingerWestphal
nuclei
what is papillodema
as intercranial pressure increases the swelling is communicated onto the optic nerve head
this can be seen on fundoscopy
