Retina and vision physiology

Question 1

WHAT TEAM?!

Answer 1

WILDCATS!!!

Question 2

sequence of events that must occur in order to see an object (4)

Answer 2

• pattern of object must fall of vision receptors
• amount of light entering the eye must be regulated
• energy from waves of photons must be transduced to electrical signals
• brain must revive and interoperate signals

Question 3

state the direct pathway for signal transmission in the retina
-other cells involved in the pathway and what they pass impulses to and from?

Answer 3

ganglion cells –> bipolar cells to –> photoreceptors
-horizontal cels (input from photoreceptors & project to other photoreceptors & bipolar cells)
amacrine cells receive input from bipolar cells and and pass on to ganglion cells, bipolar cells and other ganglion cells

Question 4

What do photoreceptors do?

-describe the structure

Answer 4

• carry out transduction

- 4 regions: synaptic terminals, cell body, inner segment, outer segment

Question 5

phototransduction

• what is the resting membrane potential in photoreceptors and why is this significant
• what happens on light exposure?
• what is the dark current?

Answer 5

• depolarised resting membrane potential compared to other neurones which have a more + Vm
• the Vm hyperpolarises
• a cGMP gated Na channel which is open in the dark and closed in the light

Question 6

visual pigment molecules

• called?
• consists of what

Answer 6

• rhodopsin (in rods), present in membrane folds

- consists of opsin, a G-protein coupled receptor + Vit A derivative

Question 7

molecular mechanism of phototransduction

describe (4)

Answer 7

aII-trans-retinal activates transducin which causes molecular cascade and decreases cGMP,
leading to closure of CGMP gated NA channels and
lowered Na entry causing hyperpolarisation

Question 8

what determines visual acuity?

• rods and cones responsable for seeing in what light
• what is high convergence and what photoreceptor is involved?

Answer 8

-photoreceptor spacing and refractive power
distribution of rods and cones

-rods- dim light
cones- daylight

-lots of rods convert onto one ganglion while few cones converge onto one ganglion

Question 9

colour vision

what cells perceive colour?

Answer 9

Cones

short/middle/long wave cone and different wave lengths activate different cones to perceive colour

Question 10

describe the differences between rods and cones

• colour
• position in retina
• convergence
• light sensitivity
• visual acuity

Answer 10

Rods:
achromatic
peripheral retina
high convergence
high light sensitivity
low visual acuity

Cones:
chromatic
central retina
low convergence
low light sensitivity
high visual acuity