Physiology Vision

Question 1

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

Answer 1

ganglion cells FIRST
bipolar cells
photoreceptors

Question 2

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

Answer 2

photoreceptors
bipolar cells
ganglion cells

Question 3

what do horizontal cells in the retina do

Answer 3

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

Question 4

what do amacrine cells in the retina do

Answer 4

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

Question 5

what is the dark current

Answer 5

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

Question 6

what does light convert 11-cis-retinal to

Answer 6

all-trans-retinal (activated form)

Question 7

what is rhodopsin

Answer 7

opsin + 11-cis-retinal

Question 8

what is present in the dark that allows the dark current

Answer 8

cGMP - allows sodium channel to open= depolarisation

in light cGMP decreases so Na channel closes

Question 9

what is the role of rods and cones

Answer 9

rods- dim light

cones- colours

Question 10

where is there highest visual acuity- how

Answer 10

in fovea of eye - highest conc of cones

Question 11

is there more convergence in rods or cones

Answer 11

more convergence in rods- increases sensitivity but decreases acuity

Question 12

what is convergence

Answer 12

number of photoreceptors communicating with a ganglion cell

Question 13

what allows you to see different colours

Answer 13

different opsins for discrete wavelengthd

Question 14

are rods or cones chromatic

Answer 14

cones

rods are achromatic

Question 15

where in retina are the cones and rods

Answer 15

rods- peripheral retina

cones- central (fovea)

Question 16

do rods or cones have higher light sensitivity

Answer 16

rods have high sensitivity

cones low

Question 17

what are the ‘off’ and ‘on’ pathways

Answer 17

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

Question 18

what is the role of lateral inhibition in the retina

Answer 18

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

Question 19

explain the receptive field of the retina

Answer 19

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

Question 20

what is retinotopy

Answer 20

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

Question 21

fibres from what visual field cross at the chiasm

Answer 21

nasal half of each retina so temporal visual field

Question 22

how is the visual field organised

Answer 22

visuotopic- scaling not consistent- fovea has a large area

Question 23

what is the path of the optic radiations

Answer 23

from lateral geniculate nucleus to layer 4 of the visual cortex

Question 24

what is V1

Answer 24

brodmans area 17- visual cortex

Question 25

what is layer four of the visual cortex

Answer 25

main input area

Question 26

what is the alpha layer of the visual cortex

Answer 26

movement ganglion layer

Question 27

what is the beta layer of the visual cortex

Answer 27

parasol ganglion cells

Question 28

what is the striate cortex

Answer 28

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

Question 29

what is the competition hypothesis

Answer 29

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)