Visual System

Question 1

4 regions of the retina

Answer 1

1. Retina
2. Macula
3. Fovea
4. Optic disk

Question 2

What are the 3 main layers of the retina

Answer 2

1. Photoreceptors
2. Bipolar cells
3. Ganglion cells

Question 3

3 regions of photoreceptor cells

Answer 3

1. Outer segments
2. Inner segments
3. Synaptic terminals

Question 4

4 features of rod cells

Answer 4

1. Monochromatic
2. Able to detect a single photon
3. So function only in dim light
4. Found mainly in periphery of retina

Question 5

3 features of cone cells

Answer 5

1. Sensitive to red, green or blue light (combined firing patterns cause colour)
2. Central in retina
3. Crucial for detail and colour vision

Question 6

Describe the fovea

Answer 6

1. Thinnest region, lateral displacement of cells above cones
2. No rods

Question 7

What neurotransmitter do photoreceptors use?

Answer 7

Glutamate

Question 8

What makes the optic nerve?

Answer 8

Axons of ganglion cells

Question 9

Where does the optic nerve synapse

Answer 9

1. 90% goes to to lateral geniculate nucleus (LGN) of the thalamus -> visual cortex
2. 10% goes to superior colliculus

Question 10

At what point does partial decussation occur

Answer 10

At the optic chiasm

Question 11

What are the two halves of the retina

Answer 11

Lateral: temporal
Medial: nasal

Question 12

Which part of the visual field decussate

Answer 12

Temporal potion will always stay ipsilateral

Question 13

Why do the optic tracts decussate

Answer 13

1. Left processes info from the right VF and visa versa

2. Always binocular vision

Question 14

Describe photoreceptors when stimulated

Answer 14

1. Steady release of glutamate in the dark
2. Light hyperpolarises
3. Prevents glutamate release
4. Change in glutamate affects bipolar cells

Question 15

What is an antagonistic center-surround receptive field

Answer 15

1. Central cells but also surround cells
2. Light hitting surround cells will have an opposite effect to center cells via horizontal cells
3. Multiple recorders for each bipolar

Question 16

Two types of ganglion cells

Answer 16

On: glutamate hyperpolarises

Off: glutamate depolarises

Mediated by different glutamate receptors

Ganglion cells match bipolar cells

Question 17

In the dark…

Answer 17

1. Photo receptor will depolarise
2. Glutamate will increase
3. Off will depolarise
4. On will hyperpolarise

Question 18

Two types of Ganglion cells?

Answer 18

Parvocellular - P cells

Magnicellular - M cells

Question 19

Describe P cells

Answer 19

1. Largely cone input
2. Small receptive field
3. High spatial resolution
4. Colour sensitive

Question 20

Describe M cells

Answer 20

1. Largely rod input
2. Large receptive fields
3. Sensitive to movement
4. Sensitive to contrast
5. Insensitive to colour

Question 21

Where do ganglion cells synapse

Answer 21

Thalamus

Question 22

What are cortical simple cells (in the primary visual cortex)

Answer 22

Will only respond to light aligned with the long axis of the receptive field

Question 23

Where are cortical simple cells found

Answer 23

Layer 4

Area B1

Primary visual cortex

Question 24

Where do cortical simple cells synapse

Answer 24

These pick up light/dark boarder crossing a receptive field

Question 25

Deceive the arrangement of simple cells in the visual cortex

Answer 25

1. Preferred orientation for cells remain in same column of cortex
2. Cells in each column respond to input from an specific eye