Visual systems

Question 1

What are the 3 layers in the retina called?

Answer 1

1. ganglion cell layer
2. nuclear cell layer
3. photoreceptors

Question 2

Differences between rods and cones

Answer 2

Rods are more sensitive to light, and are more abundant in the periphery of the retina
Cones enable us to see colour and are more abundant in the fovea

Question 3

What are the 4 main stages of phototransduction?

Answer 3

1. Light bleaches rhodopsin
2. Transducin is activated
3. PDE is activated
4. PDE activity decreases the cGMP level
5. Na+ channels shut= membrane hyperpolarises

Question 4

Difference between on and off bipolar cells

Answer 4

ON-
depolarises in response to light
have metabotropic receptors
OFF-
hyperpolarises in response to light 
have ionotropic receptors

Question 5

What are the main differences (in responses) between the centre and the surround of the receptive field?

Answer 5

Centre-
direct input from photoreceptors
bipolar cells behave normally
Surround-
indirect input from photoreceptors through horizontal cells
bipolar cells behave in the opposite way to usual