The Retina Flashcards
What does light travel through before it reaches photoreceptors
ganglion and bipolar cells
What absorbs light that has passed through the retina
pigmented epithelium
What do ganglion cells receive
output from the retina
What do amacrine cells influence
ganglion cells, bipolar cells, other amacrine cells
What do amacrine cells recieve
input from bipolar cells
What is the function of bipolar cells
connect to photoreceptors to ganglion cells
What do horizontal cells receive
input and output from photoreceptors, output to bipolar cells
What are photoreceptors
sensory transducers
Describe the structure of photorecetors
membrane invaginations, membranous disks
What do the membranous disks in photoreceptors contain
light sensitive photopigments
What is the function of photopigments
absorb light
TRUE or FALSE - monochrome and colour can be detected by the same system
FALSE
What do rod photoreceptors detect
light
What is the more numerous photoreceptor
rods
Describe the characteristics of rod photoreceptors
low visual acuity/resolution
What is the function fo rod photoreceptors
enable vision in low light
What is the photopigment associated with rods
rhodopsin
What are cone photoreceptors used for
colour
Describe the characteristics of cone photoreceptors
high visual acuity/resolution, lower sensitivity
Where is the concentration of cone photoreceptors highest
fovea
What are the cone photopigments
three varieties of opsin - S, M, L
Describe the characteristics of the fovea
low convergence, low sensitivity, high resolution
Describe the connection of cones in the fovea
each cone connected to ONE ganglion
Describe the characteristics of the peripheral retina
high convergence, high sensitivity, low resolution
What is the connection to ganglion cells in the peripheral retina
lots of rods to one ganglion
Describe the receptive field of ganglion cells in peripheral retina
large receptive field
What is the retinal ganglion photopigment
melanopsin
What is the effect of light on photoreceptors
hyper-polarisation
What is the resting potential of photoreceptors
-35mV
What channels are open in the dark
cGMP gated non selective cation channels
Describe the movement of ions in photoreceptors in the dark
Na+ moves in - depolarisation
How does light affect cGMP levels
increased light decreases cGMP levels
Describe the movement of ions into photoreceptors in presence of light
X Na+ influx - hyper polarisation
What activates rhodopsin
light
What does active rhodopsin stimulate
G protein transducin into transducin GTP
What enzyme reduces cGMP levels
enzyme phosphodiesterase
What does light adaptation of photoreceptors require
calcium
What does calcium block in the dark
guanylyl cyclase
Describe the effect of NO calcium on cells
more cGMP is produced - channels open
What is the function of retinal ganglion cells
detect ambient light levels
What do retinal ganglion cells respond to
photons
What are retinal ganglion cells important for
circadian rhythm
