Physiology Vision Flashcards Preview

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Flashcards in Physiology Vision Deck (29):
1

what is the order of cells light travels through in the retina

ganglion cells FIRST
bipolar cells
photoreceptors

2

what is the order of cells the signal is transmitted through in the retina

photoreceptors
bipolar cells
ganglion cells

3

what do horizontal cells in the retina do

receive input from photoreceptors and project to other photoreceptors and bipolar cells
inhibits bipolar cells by releasing GABA- lateral inhibition

4

what do amacrine cells in the retina do

receive input from bipolar cells and project to ganglion cells, bipolar cells and other amacrine cells

5

what is the dark current

darkness causes a greater release of glutamate from photoreceptors which is passes on to bipolar cells
this causes a stream of sodium which depolarises the photoreceptor releasinf glutamate
in response to light PNa is reduced and the photoreceptor hyperpolarises

6

what does light convert 11-cis-retinal to

all-trans-retinal (activated form)

7

what is rhodopsin

opsin + 11-cis-retinal

8

what is present in the dark that allows the dark current

cGMP - allows sodium channel to open= depolarisation

in light cGMP decreases so Na channel closes

9

what is the role of rods and cones

rods- dim light
cones- colours

10

where is there highest visual acuity- how

in fovea of eye - highest conc of cones

11

is there more convergence in rods or cones

more convergence in rods- increases sensitivity but decreases acuity

12

what is convergence

number of photoreceptors communicating with a ganglion cell

13

what allows you to see different colours

different opsins for discrete wavelengthd

14

are rods or cones chromatic

cones
rods are achromatic

15

where in retina are the cones and rods

rods- peripheral retina
cones- central (fovea)

16

do rods or cones have higher light sensitivity

rods have high sensitivity
cones low

17

what are the 'off' and 'on' pathways

off pathway bipolar cells release ionotropic glutamate, are hyperpolarised by light

on pathway bipolar cells release metabotropic glutamate
are depolarised by light

can be on- centre/ off- surround or vice versa

18

what is the role of lateral inhibition in the retina

exaggerates the difference in stimulus intensity detected by adjacent neurones (parallel neural pathways), aids in locaisation

19

explain the receptive field of the retina

two concentric circles create a centre e.g.an on centre/ off surround field:

surround field:
in centre are 'on' photoreceptors
surround are 'off' photoreceptors

when light hits centre of field firing rate (photoreceptors are hyperpolarised) is maximal
when the light extends out towards the surround there is lateral inhibition and the firing returns to a baseline level
when light only on surround not centre then firing is suppressed

20

what is retinotopy

the mapping of visual information from the retina to neurons in the brain

21

fibres from what visual field cross at the chiasm

nasal half of each retina so temporal visual field

22

how is the visual field organised

visuotopic- scaling not consistent- fovea has a large area

23

what is the path of the optic radiations

from lateral geniculate nucleus to layer 4 of the visual cortex

24

what is V1

brodmans area 17- visual cortex

25

what is layer four of the visual cortex

main input area

26

what is the alpha layer of the visual cortex

movement ganglion layer

27

what is the beta layer of the visual cortex

parasol ganglion cells

28

what is the striate cortex

the part of the occipital cortex that receives the fibers of the optic radiation from the lateral geniculate body and is the primary receptive area for vision

29

what is the competition hypothesis

Connections from the two eyes compete with each other in cortex
In the cortex, monocular deprivation during a ‘critical period’ in development results in active afferents from one eye and lower activity from the other eye (leads to alteration in the structure of the cerebral cortex)