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Principles of Neuroscience > L7 & 8 - Vision > Flashcards

L7 & 8 - Vision Flashcards

1
Q

Outer layer of eye

A

Sclera and cornea – strong layer

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2
Q

Orange patch in retinal scan is

A

Macula – controls central vision: reading text, faces

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3
Q

CASE STUDY: Trouble seeing at night, car accidents, can read ok. What was wrong with Joan?

A

Retinitis pigmentosa – macula is fine but everything else is not
-rare 1:5000. Genetic defect in rhodopsin or proteins involved in phototransduction -> lose rods -> tunnel vision -> poor peripheral vision

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4
Q

In the light, is the pupil larger or smaller?

A

Smaller -> clearer vision

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5
Q

3 Layers of retina (superficial to deep)

A

Rods (Scoptopic), cones (photopic), GCs

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6
Q

Cones vs rods, which one is more sensitive

A

Rods

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7
Q

Process of phototransduction

A

DARK:
cGMP gates a Na+ channel, causing influx of Na+ -> depol

LIGHT:
Light activates Rhodopsoin -> Transducin -> Phospho diesterase -> breaks cGMP TO GMP -> hence Na+ channel closed -> no Na+ influx and it hyperpolarises
*11- cis retinal (has a kink) is sitting in middle of Vitamin A -> light hits -> change in conformation to All-trans retinal

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8
Q

What NT is used by photoreceptors?

A

Glutamate

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9
Q

Photoreceptors respond to light with graded changes in membrane potential or ap?

A

Membrane potential - as they don’t need to communicate over large distances hence no need for AP

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10
Q

How many types of bipolar cells?

A

1 Rod bipolar, 9 cone-bipolar cells

They are important for spatial vision and colour vision

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11
Q

What do the ON, OFF, M, P ganglion cells interact with?

A

ON or OFF – if they depolarise or hyperolarise with light

Magnocellular (5 %)- motion, Parvocellular (90%)– shape and details

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12
Q

Only cell type in retina that can fire AP

A

GCs

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13
Q

How do ganglion cells respond to light?

A

Increasing or decreasing their AP firing rate

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14
Q

Receptive field of a ganglion cell is:

A

The area of retina that when stimulated with light, changes the cells membrane potential

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15
Q

How many types of GCs?

A

20

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16
Q

BP to GC pathway is parallel or series?

A

Parallel

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17
Q

Lateral inhibition: horizontal cells

A

BOTH input and output onto photoreceptors, use NT: GABA, respond to light by hyperpolarizing

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18
Q

Lateral inhibition: amacrine cells

A

34-5 types, Amarcrine is Greek for Axonless cells, inhibitory cells (release inhibitory NTs: glycine, GABA)

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19
Q

Which lateral inhibition cells are involved in motion?

A

Amacrine cells

20
Q
  • Ganglion cells are especially tuned for edges
  • If you look slight off-center at a star, you’ll see more stars, hence more rods off centre (8 degrees)
  • Rods – Rhodopsin
  • Cones – Cone-opsins
  • Opsins bind to vitamin A (all-trans Retinal)
A
  • Ganglion cells are especially tuned for edges
  • If you look slight off-center at a star, you’ll see more stars, hence more rods off centre (8 degrees)
  • Rods – Rhodopsin
  • Cones – Cone-opsins
  • Opsins bind to vitamin A (all-trans Retinal)
21
Q

CASE STUDY: Why can’t David see properly? (Has a translucent white curtain obscuring the upper part of this vision, motion perception was off, lost a quadrant in his visual field, and doesn’t have facial recognition)

A

Lesion affecting the fusiform gyrus (area IT). Also caused a visual field defect.

22
Q

M (parasol) GC

A

-Magnocellular= large, large receptive fields, M for motion detection, flicker and analysis of gross features, 5% of GC are M cells

23
Q

P (midget) GC

A

-Parvocellular = small, visual acuity and colour vision, 90% of GC are O cells

24
Q

Output target of GCs

A

Many brain regions, mainly lateral geniculate nucleus aka thalamus

25
Q

The visual pathway

A

Retina -> optic nerve -> optic tract -> LGN -> Optic radiations -> Visual cortex

26
Q

Optic Chiasm – what forms it and where is it located and the clinical significance of the location

A

Chiasm comes from latin meaning “cross”.
Fibres from left and right optic nerves combine to form it. Lies at the base of the brain, anterior to the pituitary gland, internal carotid arteries found laterally. If diseases affect these two regions, it will compress the optic chiasm and cause issues.

27
Q

Referring to the motor system, if you have a stroke on your left side of brain – it affects the right side of body. What’s different in the visual system?

A

Right visual hemifield (right half of both eyes) is viewed by left hemisphere – going to left visual cortex, left visual hemifield is viewed by right hemisphere – going to the right visual cortex

28
Q

Nasal fibres (found medially in both eyes) cross at optic chiasm. Temporal fibres (found laterally in both eyes) do not

A

Nasal fibres (found medially in both eyes) cross at optic chiasm. Temporal fibres (found laterally in both eyes) do not

29
Q

Where do the nasal and temporal fibres synapse?

A

LGN

30
Q

How many layers in LGN and what cell types are they?

A

Six
1,2 = Magnocellular layers (1 layer is for right eye, 1 for left)
3-6 = Parvocellular layers (2 for left, 2 for right)
*There is no communication between both eyes in the LGN, they are in separate layers

31
Q

Optic radiations and where are they located?

A

White matter tract formed by axons of LGN that sends info from LGN to primary visual cortex. Located in temporal lobe, partially in parietal lobe.

32
Q

Where is the primary visual cortex aka Broadmanns area 17 located?

A

Occipital lobe around the calcarine fissure.

33
Q

Central vision is located in which area of visual cortex

A

Most posterior part of visual cortex – it is a retinotopic organization

34
Q

How many layers in primary visual cortex? Which layer does LGN input go to?

A

6 (Layer 1 is surface of brain – layer 6 is inside of brain). 4c

35
Q

Cortical neurons: Orientation selectivity

A

Neurons respond best to bars moving in particular orientation

Placed electrode into visual cortex from layer 1 to 6, they all responded to the same bar of light in the same orientation, receptive field in the same location as well. NOT square matrix organisation but more fluid

36
Q

Ocular dominance columns

A

Input from LGN is segregated into small regions of the primary visual cortex called an ocular dominance column

37
Q

Segregation of info from different types of LGN cells

A

M type GC/LGN input to Layer 4C alpha

P-type GC/LGN input to Layer 4C beta

38
Q

Mixing of info from each eyes occurs in layers

A

4B and 3

39
Q

CASE STUDY: Old woman that can’t cross the road and cars appear out of “nowhere. Pouring coffee is very difficult – appears frozen to her until cup overflows. Visual acuity, colour vision and visual fields are normal. Where in the visual pathway is her lesion?

A

She can’t see motion. Lesion affecting mid temporal lobe (Area MT)

40
Q

After primary visual cortex, where is the visual info encoded?

A

After primary visual cortex, where is the visual info encoded?
2 streams. Dorsal pathway (where?) and ventral pathway (what?)
*Dorsal is superior half of brain and ventral is inferior

41
Q

Area MT

A

Middle temporal lobe is an area specialised for processing object motion

  • Receives retinotopic information from a number of cortical areas including V2 and V3
  • Receives input from cells in Layer IVB of the primary visual cortex (M type GCs/LGN)
42
Q

Ventral stream

A

V1, V2, V4

  • From calcrine fissue, starts from V1 and travels via V2 and V3 down to inferior parts of temporal lobe
  • Important for perception of shape and colour, object recognition
43
Q

Area IT (inferior temporal)

A

A major output of Area V4

  • Neurons respond to a wide variety of abstract shapes and colour
  • Important for visual memory and perception
  • Important for perception of faces
44
Q

If only one eye can’t see, area affected is ____ optic chiasm

A

Between the eye and the optic chiasm, it is before the chiasm

45
Q

If there is a defect on the same side of both eyes, are affected is ____ optic chiasm

A

After chiasm

46
Q

Both eyes but on the opposite sides (medially)

A

Optic chiasm

Principles of Neuroscience (25 decks)

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