Vision

Question 1

Retina

Answer 1

Covers most of the globe of the eye. Light comes through ganglion output layer, middle layer (bipolar cells) and finally rods and cones.
Not uniform. There is a blind spot.

Question 2

Major problem in

Answer 2

High resolution snaps into 2D. Dont know how this works.

Question 3

Rods and cones

Answer 3

Both have outer segments contains photo pigment. Cone is indented. Operate in different ways. Hyperpolarize when activated. Smaller response in cone to same stimulus - Short reponse. Rod much longer.
In dark only rods are operating. Cones absorbing photons but signal generated is too late.

Question 4

60hZ - Perceivable light

Answer 4

Can perceive flickering lights. Temporal resolution of rod vision is much poorer than cone vision.

Question 5

Retinal

Answer 5

Vitamin A derivative - crucial element in photo transduction.

Question 6

Photopigment

Answer 6

Amino acids bind retinal. To allow transconfiguration. Different wave lengths and different energies.

Question 7

Photopigment

Answer 7

Amino acids bind retinal. To allow transconfiguration. Different wave lengths and different energies. Alterations in molecule lead to problems with colour recognition.

Question 8

Photo-isomerisation

Answer 8

look at this.

Question 9

Transduction: Cascade

Answer 9

Electrode over a rod (amphibian retina) and leave photo receptor in dark for short amount of time 45 mins then give very low light. Gives a bumpy response in polarization, Dark adapted rod show responses and can detect photons.

• Light adaptation - put in room of constant back ground intensity, then what flash will they detect? Size of flash needed is proportional to background. Rod range you cant detect until certain illuminance.
• Dark adaptation

Question 10

For humans to detect a flash after the dark.

Answer 10

6 photons simultaneously detected. 6 photo receptors to receive.

Question 11

Transduction cascade: Activation

Answer 11

G-Protein (transducin molecules), Cyclic GMP, Hyper-polarisation, Sites of amplification, Sites of regulation.
Something to do with phosphodiesterase.

Question 12

Transduction cascade: inactivation

Answer 12

Role of calcium. Rhodopsin inactivation, Guanylate cyclase.

Question 13

On vs Off pathways.

Answer 13

Some cells respond to flash of light going on and flashing light off - at bipolar cells.
Small spot of light on the right place in receptive retina = lots of AP.
Bright spot with brighter background = no AP.
Broad spot of light = weaker response.
Spatial pattern to receptive field of retinal bipolar cell.

Question 14

Retinal processing: centre-surround

Answer 14

Sensitive to relative different spatial luminance not to overall luminance. Mexican hat. Higher in centre and weaker in surround.

Question 15

Primate fovea

Answer 15

P (cellular projection and M (project to magna cells) retinal cells. Mouse doesn’t have these. But use vision in different ways. They can see in ultraviolet.
We cant see in infrared.
Dendritic cells increase with distant away from fovea - highest density of ganglion cells.