Lecture 12: Vision 1

Question 1

Describe the different layers of the retina

Answer 1

10) inner limiting membrane
9) nerve fiber layer - axons of ganglion cell converging at optic disk
8) ganglion cell layer - ganglion cell bodies
7) inner plexiform layer - synapses between interneurons and ganglion cells
6) inner nuclear layer - cell bodies of bipolar cells and amacrine and Muller cells
5) outer plexiform layer - synapses between photoreceptors and interneurons
4) outer nuclear layer - cell bodies of photoreceptors
3) Outer limiting membrane - tight junctions between glial cells and inner segments of photoreceptors
2) Photoreceptor Layer - outer segments of rods/cones
1) Retinal Pigment Epithelium - contains melanin, where retinal is regenerated, prevents transverse scatter

Question 2

Describe the phototransduction pathway

Answer 2

Light converts retinal from 11-cis to all-trans, this activates rhodopsin, the GPCR with a retinal binding site in K296 in helix 7. Activates transducin (G protein) which activates phosphodiesterase, which converts cGMP to GMP. This closes CNG channels and prevents depolarization, therefore no glutamate is released

Question 3

How is the chromophore regenerated?

Answer 3

Occurs in the retinal pigment epithelium, carried back to the photoreceptor by retinoid binding proteins

Question 4

Discuss differences between rods and cones

Answer 4

rods have much higher density of opsin
photoreceptors active at different frequency due to different amino acid sequence
cones much more dense at the fovea