W2: Retina

Question 1

Describe the vitreous humour

Answer 1

Located in main cavity posterior to lens
Pins retina to back of eye

Question 2

Why is the retina back to front?

Answer 2

Retinal Pigmented Epithelium isn’t transparent and requires nourishment from the photoreceptors

Question 3

Describe Rods and Rod only vision

Answer 3

Dim conditions (Scotopic - rod only)
90 million in periphery between 12-15 degrees
High sensitivity

Question 4

Describe cones

Answer 4

Bright conditions - (Photopic cones only)
5 million - in central fovea
Blue (420nm) Green (530nm) Red (560nm)

Question 5

Describe the Purkinje shift

Answer 5

Shift from photopic (bright) to scotopic (dark) vision
Peak light sensitivity shifts 555nm to 510nm

Question 6

Describe the glutamate and ganglion cell response in ON/OFF bipolar cells

Answer 6

In Light: photoreceptors decrease GLU release (OnBi Like)
In Dark: photoreceptors increase GLU release (OffBi Like)
Increased GLU increases ganglion cell firing rate

Question 7

Describe ganglion cells which are light sensitive

Answer 7

Intrinsically Photosensitive Retinal Ganglion Cells make up 2% of total which contain blue-sensitive melanopsin
Project to areas affecting circadian rhythm/cognition/mood

Question 8

What is a visual receptive field?

Answer 8

Region of visual field where a stimulus modulates the firing rate of the neuron
Photoreceptors cells feed into bipolar cells affecting ganglion cell firing rate

Question 9

Explain centre-surround opponency

Answer 9

Centre and surround of receptive field have opposing effects mediated by horizontal/amacrine cells

Question 10

Describe the location/function of:
Ganglion Cells, Bipolar Cells, Horizontal Cells, Rods, Cones

Answer 10

Ganglion Cell: GC Layer - final retinal output neurone
Bipolar Cells: Inner Nuclear Layer - connects ganglion cells to photoreceptors
Horizontal Cells: Outer Plexiform - CSO
Rods - dim light
Cones - bright light
Rods/Cones in Inner-Segment-Outer-Segment Layer

Question 11

Where does the optic nerve project to and explain the functions

Answer 11

LGN
Superior Colliculus (eye movement)
Suprachiasmatic Nucleus (circadian rhythm)
Pretectum (control pupil size)

Question 12

Describe 5 differences between the fovea and other parts of the retina

Answer 12

Indented and densely packed with cone photoreceptors only, smaller receptive fields
Neural layers in front displaced to reduce scattering