Vision Physiology Flashcards
Which cells are most deep in the retina?
photoreceptors
what is the function of photoreceptors?
convert electromagnetic radiation to neural signals
What happens to the polarisation of photoreceptors when light shines on them?
hyperpolarizes
What is the dark current?
A slightly more positive current caused by a Na+ channel that is open in the dark and closed in the light
What is the main visual pigment?
rhodopsin
What does light do to rhodopsin?
converts it to active form of all-trans-retinal
In the dark, is there more or less glutamate?
More
Is phototransduction a high or low gain mechanism?
High gain - 1:1000
What determines visual acuity?
photoreceptor spacing and refractive power
What is the receptive field?
the part of the retina that needs to be stimulated to elicit action potentials form a ganglion cell.
What are rod cells useful for?
seeing in dim light
What are cones useful for?
seeing in normal daylight
What is high convergence?
more cells per ganglion cell - increases sensitivity but reduced acuity (periphery)
What is low convergence?
less cells per ganglion cell - decreased sensitivity but increased acuity (fovea)
Rods can sense colour - T/F?
False
Where are cone cells found in highest density?
central retina (fovea)
Where is higher visual acuity in the retina?
fovea
What is the function of ON and OFF bipolar and ganglion cells?
respectively detect increases and decreases in luminance
Which process allows for stimulus localisation and intensity?
lateral inhibition
What is centre surround organisation?
maximally active with a ganglion centre dark only
What is the purpose of lateral inhibition?
to emphasise areas of difference and sharpen the boundary.
