Visual pathways and lesions

Question 1

what is the LGN

Answer 1

lateral genticulate nucleus which is a relay center in the thalamus for the visual pathway

receives input from the retina

Question 2

what is the optic radiation

Answer 2

a collection of axons from relay neurons in the lateral genticulate nucleus of the thalamus to the visual cortex aka striate cortex

Question 3

what is perimetry

Answer 3

the measurement of visual field function

Question 4

what is the result of a lesion of the left optic nerve

Answer 4

just the left border of the visual field is lost

Question 5

what is the result of a lesion in the left optic tract

Answer 5

the whole right half of the visual field is lost

Question 6

what is the effect of a lesion in the left temporal occipital area

Answer 6

the whole right half of the visual field is lost, as with the optic tract

Question 7

what is the result of a lesion in the optic chiasm

Answer 7

the left and right borders of the vision will be lost due to the fact that all peripheral vision crosses over at the chiasm

Question 8

bitemporal heteronymous hemianopsia

Answer 8

vision is missing in the outer half of both the right and left visual field.

caused by an optic chiasm lesion

Question 9

what is the contralateral homonymous hemianopia

Answer 9

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

Question 10

what is contralateral superior quadrantanopia

Answer 10

upper quarter of the visual field is lost on the same side

Question 11

what state are cones and rods in in the dark

Answer 11

depolarised

Question 12

what do depolarised rods and cones relesase

Answer 12

neurotransmitter

this is known as dark current

Question 13

what is the neurotransmitter involved in vision

Answer 13

glutamate

can be excitatory or inhibitory to the bipolar cell

Question 14

what are horizontal cells

Answer 14

connect multiple rods or cones to single or groups of bipolar cells

Question 15

are horizontal and amacrine cells inhibitory or excitatory

Answer 15

inhibitory

Question 16

what is the function of the lateral connections in amacrine and horizontal cells

Answer 16

lateral inhibition which sharpens contrast and provides edge detection

Question 17

what is the role of ganglion cells

Answer 17

project information from the retina to the thalamus (LGN)

Question 18

describe the information processing that goes on in the retina

Answer 18

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

Question 19

what happens to information that leaves the optic tract and passes to the pretectal nuclei in the midbrain (10%)

Answer 19

used for eye movement towardsa novel stimulus for tracking

enables light on the retina to stimulate eye movements that put it over the fovea

Question 20

what is the function of the LGN

Answer 20

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

Question 21

decribe retinotropy

Answer 21

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

Question 22

describe how output from the LGN is modified or filtered

Answer 22

incoming information from the cerebral cortex, thalamic nuclei and brainstem reticular formation

Question 23

where is the primary visual cortex

Answer 23

medial surface of the occipital lobe around the calcarine fissure, has a striped appearance

Question 24

describe the histology of the striate cortex

Answer 24

multilayered with different layers performing different tasks

6 layers with 3 sublayers = 9 in total

Question 25

what are the three main functions in the primary visual cortex

Answer 25

colour recognition ocular dominance orientation detection

Question 26

what are blobs

Answer 26

columns of cells associated with colour recognition can be stained with cytochrome oxidase

Question 27

what are dominance strips

Answer 27

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

Question 28

what is stereopsis

Answer 28

perspective and the relative size of objects

Question 29

what is the temporal lobe stream

Answer 29

the temporal lobe is involved in identifying what something is

Question 30

where is the Where system located

Answer 30

parietal cortex- involved in object location and spatial relations i can be possible to perceive an object but not know where/ what it is

Question 31

what is integrative or object orientation agnosia

Answer 31

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

Question 32

what are the funcitons of the Where system

Answer 32

1. Navigation through the environment – a mapping of object around us 2. Movement of eyes to locate and follow objects in our field of view 3. Interpretation of motion and perspective in the World around

Question 33

what is the retinotectal pathway

Answer 33

Pupillary light reflex pretectal neurons project to ipsi- and contralateral EdingerWestphal nuclei

Question 34

what is papillodema

Answer 34

as intercranial pressure increases the swelling is communicated onto the optic nerve head this can be seen on fundoscopy