Phototransduction

Question 1

name the layers of the retina in the order they are hit by incoming light

what is in each layer?

Answer 1

ganglion layer
outer plexiform (amacrine cells, synapses between ganglion and bipolar cells)
outer nuclear (nuclei of bipolar cells)
inner plexiform (horizintal cells, synapses between bipolar and photoreceptor cells)
inner nuclear (nuclei of photoreceptor cells)
photoreceptor

Question 2

which cells transduce receptor potentials?

Answer 2

photoreceptors

bipolar cells

Question 3

describe the process of phototransduction in the absence of light

Answer 3

1. cis-retinal is unable to activate transducin
2. transducin is unable to activate PDE
3. PDE is unable to inhibit the activity of guanyl cyclase
4. cGMP > GMP
5. cGMP opens Na and Ca ion channels
6. release of glutamate into the synapse
7. excitatory post-synaptic potential generated

Question 4

describe the process of phototransduction in light

Answer 4

1. cis-retinal converted to all-trans-retinal, which atcivates transducin
2. transducin activates PDE
3. PDE breaks down cGMP into GMP
4. GMP > cGMP
5. ion channels do not open
6. no release of glutamate
7. inhibitory post-synaptic potential generated

Question 5

describe the function of horiztonal cells

Answer 5

activated by glutamate released by photoreceptors in the absence of light, release GABA onto adjacent photoreceptors to further decrease glutamate release in the presence of light (spot/annulus light)

Question 6

what is a receptive field and how is it organised?

Answer 6

a group of photoreceptors that activate the same bipolar and ganglion cell
centre, surround

Question 7

what are on-centre bipolar cells?

Answer 7

express mGluR6 (sign-inverting inhibitory Glu receptor)
DEactivated by glutamate

Question 8

what are off-centre bipolar cells?

Answer 8

express AMPA (sign conserving activatory Glu receptor)
activated by glutamate