Physiology Vision Flashcards Preview

Neurology > Physiology Vision > Flashcards

Flashcards in Physiology Vision Deck (29)
Loading flashcards...

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

ganglion cells FIRST
bipolar cells


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

bipolar cells
ganglion cells


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


what do amacrine cells in the retina do

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


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


what does light convert 11-cis-retinal to

all-trans-retinal (activated form)


what is rhodopsin

opsin + 11-cis-retinal


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


what is the role of rods and cones

rods- dim light
cones- colours


where is there highest visual acuity- how

in fovea of eye - highest conc of cones


is there more convergence in rods or cones

more convergence in rods- increases sensitivity but decreases acuity


what is convergence

number of photoreceptors communicating with a ganglion cell


what allows you to see different colours

different opsins for discrete wavelengthd


are rods or cones chromatic

rods are achromatic


where in retina are the cones and rods

rods- peripheral retina
cones- central (fovea)


do rods or cones have higher light sensitivity

rods have high sensitivity
cones low


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


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


explain the receptive field of the retina

two concentric circles create a centre 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


what is retinotopy

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


fibres from what visual field cross at the chiasm

nasal half of each retina so temporal visual field


how is the visual field organised

visuotopic- scaling not consistent- fovea has a large area


what is the path of the optic radiations

from lateral geniculate nucleus to layer 4 of the visual cortex


what is V1

brodmans area 17- visual cortex


what is layer four of the visual cortex

main input area


what is the alpha layer of the visual cortex

movement ganglion layer


what is the beta layer of the visual cortex

parasol ganglion cells


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


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)