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Aedin Minogue > HL7-9 Visual System > Flashcards

HL7-9 Visual System Flashcards

1
Q

Divergent pathway

A

One presynaptic neuron synapsing on many postsynaptic neurons

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2
Q

Convergent pathway

A

Many presynaptic neurons synapsing on one postsynaptic neuron

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3
Q

Optic tract is made of

A

Ganglion cell axons

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4
Q

What are the local interneurons in the retina and what do they do?

A
  1. Horizontal and amacrine cells

2. Modulate transmission onto bipolar and ganglion cells

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5
Q

Three orders of cells in the retina

A
  1. Rods & cones (photoreceptors)
  2. Bipolar cells
  3. Ganglion cells
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6
Q

Cones are for….

A

colour vision

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7
Q

Rods are for…

A

black & white

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8
Q

Cones are mostly tightly packed in the …. and sparsest in the ….

A
  1. fovea

2. periphery

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9
Q

Rods have …. spatial resolution but are … sensitive to light

A

low

very

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10
Q

Cones have …. spatial resolution but are … sensitive to light

A

high

insensitive

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11
Q

Rods contain

A

rhodopsin

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12
Q

Cones contain

A

various opsins

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13
Q

Number of rods

A

100 million

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14
Q

Number of cones

A

6 million

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15
Q

Three segments of photoreceptors

A
  1. Outer - discs of photopigments
  2. Inner - nucleus & organelles
  3. Synaptic - output to bipolar cells
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16
Q

How does light affect photoreceptors?

A
  • Photons of light are absorbed by the opsin protein which undergoes conformational change to trans config
  • the opsin then activates transducin (G protein) which causes cGMP breakdown by activating cGMP phosphodiesterase
  • cGMP sodium channels close and the cell is hyperpolarised
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17
Q

How do photoreceptors react to darkness

A
  • Darkness = no photons to trigger breakdown of cGMP

- open cGMP sodium channels = depolarisation = Glu release onto bipolar cells

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18
Q

How is rhodopsin recycled

A

-arrestin facilitates conversion of all-trans retinol back to 11-cis retinal

19
Q

How does light affect on-centre ganglions

A

increases firing

20
Q

How does light affect off-centre ganglions

A

decreases firing

21
Q

How does a decrease in Glu affect the bipolar cell

A
  • Glu binds to mGluR6 resulting in closure of cGMP-gated sodium channels
  • decreased Glu = open Na+ channels = depolarisation of bipolar cells
22
Q

The optic nerve innervates…

A
  1. Superior colliculus - controls head and eye movements
  2. Midbrain pretectal area - controls the pupil reflex
  3. Thalamus - relays to the visual cortex
23
Q

Receptive field of the retina

A

area of the retina that will change the membrane potential of the bipolar cell when stimulated by light

24
Q

Receptive field centre (retina)

A

direct input from the photoreceptor

25
Q

Receptive field surround (retina)

A

input from horizontal cell

26
Q

Under what conditions does the ganglion cell fire the most?

A

When there is greatest contrast between light illuminating the centre and surround

27
Q

Layers 1, 4, 6 of the LGN receive innervation from the … side of the retina

A

contralateral

28
Q

Layers 2, 3, 5 of the LGN receive innervation from the … side of the retina

A

ipsilateral

29
Q

Three inputs to the superior colliculi

A
  1. RGCs
  2. Visual cortex
  3. Other cortical areas (auditory, somatosensory)
30
Q

Three functions of the superior colliculi

A
  1. Integrate visual and movement input
  2. Rapid changes in visual field (detect & alter gaze)
  3. Saccades
31
Q

Retinohypothalamic Pathway

A

Projections from the retina to the pretectum and the superchiasmatic nucleus of the hypothalamus via specialised RGCs which react to light via melanopsin (cf photoreceptors)

32
Q

Three thalamic nuclei

A
  1. Relay
  2. Accessory
  3. Reticular
33
Q

Four ways that info is processed in the thalamus

A
  1. Local - in thalamic nucleus
  2. Brainstem modulation - NA, 5HT
  3. Inhibitory modulation - thalamic reticular nucleus
  4. Excitatory feedback - from cortex
34
Q

Two pathways from the retina to the LGN

A
  1. Magnocellular

2. Parvocellular

35
Q

P cells respond to ….

A

colour change

36
Q

M cells respond to ….

A

luminance contrast

37
Q

Retinotopic map

A

Spatial arrangement of retinal projections is preserved in the thalamus i.e. neighbouring cells in the retina project onto neighbouring areas of the LGN.

38
Q

4 properties V1 neurons respond to

A
  1. Colour
  2. Depth
  3. Motion
  4. Form
39
Q

Simple cells

A

V1 cells that respond best to stimuli with a specific orientation

40
Q

Complex cells

A

V1 cells that are responsive mostly to movement

Have larger RFs than simple cells

41
Q

V1 neurons are mainly concerned with…

A

object edges

42
Q

Two V1 visual streams

A
  1. Dorsal - where i.e. motion

2. Ventral - what i.e. colour & form

43
Q

Which layers generally contain simple/complex cells?

A

Simple cells - layers that receive direct thalamic input (i.e. 4 and 6)
Complex cells - layers that mostly receive cortical input i.e. 2 and 3 (input from 4) and 5 (input from 2 and 3)

Aedin Minogue (4 decks)

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