Physiology of vision

Question 1

What is the direct vertical pathway for signal transmission in the retina?

Answer 1

Photoreceptors -> bipolar cells -> ganglion cells (direction of signal, direction of light is opposite to this)

Question 2

Where to horizontal cells receive input from and project to?

Answer 2

Receive input from photoreceptors and project to other photoreceptors and bipolar cells

Question 3

Where do amacrine cells receive input from and project to?

Answer 3

Receive input from bipolar cells and project to bipolar cells, ganglion cells and other amacrine cells

Question 4

Light converts 11-cis-Retinal into what?

Answer 4

All-trans-Retinal (activated form)

Question 5

What is rhodopsin?

Answer 5

Opsin + 11-cis-retinal

Question 6

What are the features of rods?

Answer 6

Allow us to see in dim light, high convergence, high sensitivity to light, low visual acuity, found in the peripheral retina

Question 7

What are the features of cones?

Answer 7

Allow us to see in normal daylight, low convergence, colour vision, low light sensitivity, high visual acuity

Question 8

There are 3 types of cone. Name these and describe which wavelength of light they absorb

Answer 8

Short wave cone - blue light
Middle wave cone - green light
Long wave cone - red light

Question 9

What does lateral inhibition within the retina do?

Answer 9

Exaggerates the difference in stimulus intensity detected by adjacent neurons, aids with localisation

Question 10

Horizontal cells interconnect a group of surround neurons. It samples the total amount of excitation in the surround and responds by releasing GABA. If there was low surround, what would happen to the amount of GABA released?

Answer 10

Less GABA would be released. The response of the centre on bipolar cells is thus higher

Question 11

What do center-surround/lateral inhibition serve to emphasise?

Answer 11

Contrast i.e. it sharpens the boundary between objects of different luminance

Question 12

How does lateral inhibition modify the receptive fields of ganglion cells?

Answer 12

It modifies the RFs of ganglion cells to have a center surround organisation i.e. ON center - OFF surround or OFF center ON surround

Question 13

How is the retina divided relative to the fovea?

Answer 13

Divided in half into a nasal and temporal hemiretina

Question 14

What percentage of light crosses over at the optic chiasm?

Answer 14

60% cross (nasal retina) and 40% do not (temporal retina)

Question 15

What visual defect would occur due to a lesion at position A?

Answer 15

Monocular blindness

Question 16

What visual defect would occur due to a lesion at position B?

Answer 16

Bitemporal hemianopia

Question 17

What visual defect would occur due to a lesion at position C?

Answer 17

Contralateral heminopia

Question 18

What visual defect would occur due to a lesion at position D?

Answer 18

Superior quadrantopia

Question 19

What visual defect would occur due to a lesion at position E?

Answer 19

Hemianopia with foveal sparing

Question 20

First binocular neurons are found in the striate cortex. Most layer III neurons are monocular (but not layer IV) - T/F?

Answer 20

False - first binocular neurons are found in the striate cortex. Most layer III neurons are BINOCULAR, but not layer IV

Question 21

What is the competition hypothesis?

Answer 21

Connections from the two eye compete with each other in the cortex

Question 22

Why are retinal synapses in the lateral geniculate nucleus not affected by monocular deprivation?

Answer 22

Because they are monocular. In the cortex, monocular deprivation during a critical period in development results in active afferents from one eye and lower activity from the other eye