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OD1 Semester 2 - Integrated Ophthalmic Sciences and Preclinical Optometry > Retinal Receptive Fields - Week 5 > Flashcards

Retinal Receptive Fields - Week 5 Flashcards

1
Q

What is the advantage of a centre-surround detection system and how does it differ from simple detection?

A

Centre-surround receptive fields give you information on:

  • size of stimulus
  • location of stimulus

This is because one region will respond to stimulus and the other responds to stimulus inhibition

(simple detection is just photorceptors connected to bipolar cells connected to ganglion cells. Need lateral pathway)

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2
Q

How do the rods, horizontal cells and bipolar cells react to an annulus compared to a small spot stimulus?

A

Rod response is reduced, Horizontal cell response is similar, and bipolar cell response is changed

The horizontal cell is connected to all the receptors which is why it is unchanged (actually a bit bigger even because more receptors are stimulated with the annulus)

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3
Q

How does size of an annulus effect horizontal cell response?

A

Larger annulus increases the response (because more receptors are stimulated)

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4
Q

Why is there a small rod response in an annulus stimulus for a cell’s receptive field?

A

Some of the light leaks across

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5
Q

During patch clamp experiments, what happens when the light stimulus is on an excitable area?

A

Number of spikes from the patch clamp increases

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6
Q

What types of centre-surround receptive fields for ganglion cells are there?

A

On-centre Off-surround ganglion cell

Off-centre On-surround ganglion cell

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7
Q

Describe the link between the anatomy and physiology for centre-surround responses.

A

Cells can be excitatory or inhibitory for the centre/surround. So there are 2 different channels.

Anatomically: bipolar and ganglion cells synapse in 2 different layers.

(So there’s an anatomical segregation of this physiological outcome)

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8
Q

What Neurotransmitters are used by the:

  • Through pathway
  • Lateral pathway?

What type of signals do they carry?

A

Through: uses Glutamate, carries excitatory signal
Lateral: uses GABA, carries inhibitory signal

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9
Q

What 2 cells are important for the lateral pathway?

A
  • Horizontal cells

- Amacrine cells

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10
Q

Where do horizontal cells synapse?

A

Outer Plexiform Layer

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11
Q

Where are the horizontal cell bodies?

A

Inner Nuclear Layer

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12
Q

Where do amacrine cells synapse?

A

Inner Plexiform Layer

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13
Q

Where are amacrine cell bodies?

A

Inner Nuclear Layer

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14
Q

How many types of horizontal cells are there in primates (and cats)?

A

2

  • H1 and H2 in primates
  • A and B in cat
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15
Q

How many types of amacrine cells are there in primates?

A

Over 30 types in primates

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16
Q

How can info be patched from receptors to create the surround characteristics of a bipolar cell?

A

Horizontal cells are patching info from a lot of cones + some rods into nearby bipolar cells to create the surround characteristics of that bipolar cell

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17
Q

What do the different horizontal cells communicate with?

A

H1: speaks to all the cones and some of the rods
H2: only speaks to cones

also there’s a H3, which speaks to a certain subclass

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18
Q

How does the Bipolar centre-surround compare to the Ganglion cell centre-surround?

A

Bipolar cell surround is not as inhibitory (still is somewhat inhibitory though)

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19
Q

What anatomical evidence suggests that bipolar cells and horizontal cells communicate with each other?

A

They both are at the same synapse

20
Q

Where do you find lots of GABA

A

Found in both the outer and inner retina

21
Q

List the 2 classes of Glutamate receptors and explain which one is preferentially used for the ON pathway and OFF pathway.

A

1) Metabotropic receptors - goes through a series of intermediary cascades; used for ON pathway
2) Ionotropic receptors - is a direct gate of an ion channel; used for OFF pathway

22
Q

What is the resting membrane potential (mV) for Bipolar cells?

A

On and Off bipolar cells rest at slightly either side of -70

23
Q

What is the equilibrium potential (mV) for Sodium?

A

+20

24
Q

What is the equilibrium potential (mV) for Potassium?

A

-75

25
Q

What is the equilibrium potential (mV) for Chloride?

A

-70

26
Q

How are chloride channels and bipolar cells related to GABA?

A

Bound GABA opens chloride channels on bipolar cells

  • because the chloride equilibrium potential is close to the membrane potential, it can potentially have either depolarising or hyperpolarizing effects
27
Q

Where in bipolar cells is chloride the highest?

A

Highest at the bipolar cell dendrites

28
Q

How have we measured the amount of chloride in bipolar cells?

A

Use a fluorescent chlorine indicator in mice and use fluorescence microscopy

29
Q

Describe the motivations of chloride comparing ON and OFF bipolar cells?

A

On Bipolar cell: (Cl Efflux) has membrane potential slightly more than -70 therefore chloride wants to leave

Off Bipolar cell: (Cl Influx). membrane potential slightly less than -70; chloride wants to enter

30
Q

How do cones act in the dark?

A
  • Glutamate released from cones depolarises horizontal cells
  • Glut activates horizontal cell to release GABA
  • and then GABA keeps the chloride channels open
31
Q

Where is spatial sensitivity best? And why?

A

Best at the fovea
- As we go from the centre, the dendritic field of the bipolar cell gets bigger and the dendritic field of the ganglion cell gets bigger. Meaning that the number of cones feeding the centre and number of cones feeding the surround increases.

32
Q

What happens with bipolar cells when light stimulates centre and surround?

A
  • Glutamate and therefore GABA release STOPS
  • Less GABA closes chloride channels
  • now chloride is stuck in cell
    Result in:
  • Less Cl efflux from ON-BCs: which become more negative; less depolarisation response to light
  • Less Cl influx from OFF-BCs: becomes less negative; less hyperpolarisation response to light
33
Q

What happens with bipolar cells when light stimulates the centre only?

A

Glutamate release stops in centre but continues in surround, allowing for GABA release and therefore Chloride channels stay open.
ON-BC: depolarise
OFF-BC: hyperpolarise

34
Q

How do we express how strong a centre vs surround is?

A

By comparing difference of gaussian functions

35
Q

What is the highest/’cutoff’ spatial frequency dependent on?

A

Centre size

36
Q

What do low spatial frequencies affect? Centre, Surround or both?

A

Both

37
Q

What size of receptive fields help you move around your environment in day to day life?

A

Small receptive fields

38
Q

What level of contrast is needed to detect large receptive fields?

A

Need High contrast

39
Q

How many types of amacrine cells are there?

A

30 different types

40
Q

What is the role of A2 amacrine cell?

A

patch rod system onto cone system

41
Q

Where are Starburst amacrine cells found?

A

In lower mammals only

42
Q

Are starburst amacrine cells polarised or unpolarised? Explain.

A

They are polarised, meaning they have GABA receptors on the outside and excitatory receptors on the inside

43
Q

Where are the directionally-sensitive characteristics of the centre-surround system constructed in higher order mammals compared to lower order mammals?

A

Made further up in our visual system

44
Q

What is the special role of starburst amacrine cells?

A

The prefer certain centre-surrounds but also prefer DIRECTION of movement

45
Q

Where does the majority of visual processing happen in lower order mammals?

A

At the retinal level

46
Q

How can we investigate the relationship between horizontal cells and inhibitory surround?

A

Inject hyperpolarising current into the surround region to get same response as if a light were shined there

47
Q

How would applying picrotoxin influence the ganglion cell centre-surround response?

A

Picrotoxin is an antagonist of GABA receptors.

Normally, increasing spot of light size would eventually decrease the response due to the inhibitory surround. With Picrotoxin, the response stays at it’s maximal and now no longer decreases.

OD1 Semester 2 - Integrated Ophthalmic Sciences and Preclinical Optometry (49 decks)

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