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Neural Biology 1 > Retina: OPL > Flashcards

Retina: OPL Flashcards

1
Q

What are the 2 synaptic layers in the retina?

A
  • Outer plexiform layer

- Inner plexiform layer

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2
Q

What does the outer plexiform layer contain?

A

contains the synaptic endings of rods (spherules) and cones (pedicles)
-these synapse mainly with horizontal and bipolar cells

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3
Q

What is the rod synaptic ending?

A
  • is smaller and spherical
  • one invagination
  • known as spherules
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4
Q

What is the cone synaptic ending?

A
  • synaptic region of cone is quite big
  • several invaginations
  • known as pedicle
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5
Q

What is the main characterisitc of cone pedicle ?

A

-full of vesicles (vesicles of the neurotransmitter)

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6
Q

What does each pedicle contain?

A
  • Each pedicle contains ca. 25 invaginations
  • each of which is associated with a synaptic ribbon
  • these synaptic ribbon are associated with the halo vesicle
  • contains 3 synpases
  • bigger than rods synaptic ending
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7
Q

What do the synaptic ribbon do?

A

that may serve to guide vesicles to their site of release

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8
Q

What is each invagination associated with?

A

-Each invagination is also associated with a ‘triad’

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9
Q

What is a triad?

A

3 post synaptic processes

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10
Q

What do the lateral elements of a triad are provided?

A

come from horizontal cells

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11
Q

What do the central elements of a triad are provided by?

A

the less deeply invaginating central element comes from a bipolar cell

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12
Q

What does a electron micrograph of a cone pedicle show?

A

invaginations (i.e2) and associated ‘triads’ (others are out of plane of section)

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13
Q

What does a cone pedicle make contact with?

A
  • triads made up of 2 lateral elements from horizontal
    cells and central element from bipolar cells

however not all post synaptic processes on pedicles are triads.

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14
Q

What are other post synaptic contacts that dont associate with cone pedicle?

A

There are about 500 superficial (non-invaginating) contacts which come from bipolar cells in each cone

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15
Q

What are the synapses in the triad of cone pedicles?

A

have horizontal cells and bipolar cells

and then superficial contact with bipolar cells

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16
Q

What is the final contact a cone pedicle makes?

A
  • with neighbouring cone pedicles and rod spherules via ‘telodendria’. - where they contact adjacent photoreceptors (rods and cones) via electrical synapses
  • cones are able to influence surrounding photoreceptors via telodendria
  • These are electrical ‘gap’ junctions
17
Q

What is the principal of uni-variance?

A

photoreceptor only responded to light falling directly on that photoreceptor
-however now know this is not so, and that receptors can interact and neighbouring cones can facilitate the response of their neighbours

18
Q

What can Photoreceptors can influence ?

A

the electrophysiological response of neighbouring receptors.

19
Q

How can we illustrate that receptors can interact and neighbouring cones can facilitate response of their neighbours ?

A
  • cones
  • put electrode in one cone
  • shine small spot of light
  • get a given hyper-polarisation
  • if principle invariance was true in cones- if we stimulated retina with bigger spot- the size of response should be the same-would give the same response to a large and a small spot.
  • however that is not true
  • a big spot gives a much physiological/ larger response, and that can be explained by neighbouring cones must have an excitatory input (they facilitate response of photoreceptor).
20
Q

How are excitatory interactions between photoreceptors ?

A

-between photoreceptors are mediated by telodendria

21
Q

Summary of cone pedicle synaptic contacts?

A
  1. ca. 25 invaginations each associated with a ‘triad’ from horizontal and bipolar cells
  2. ca. 500 superficial contacts from bipolar cells
  3. with 6-15 neighbouring photoreceptors via telodendria
22
Q

What are the rod spherules

A
  • only have a single (1) invagination containing 2-7 postsynaptic processes so dont form triad like they do in cone pedicles.
  • the lateral elements come from horizontal cells and the central processes from bipolar cells.
23
Q

What do the horizontal cells synapse with ?

A

photoreceptors and bipolar cells in the OPL

24
Q

What do Horizontal cells have?

A

a single long thin axon (which may be too thin to conduct)

25
Q

What are the 3 types of horizontal cells ?

A

There are 3 types in the human retina;

  • H1 & H3 their dendrites contact only cones while axons synapse with rods (H3 bigger)
  • H2 dendrites and axons synapse only with cones
26
Q

What does a single horizontal cell contact in the central retina in cones?

A

A single horizontal cell contacts 6-12 cones in the central retina.

27
Q

What about a single horizontal cell synapse with rods?

A
  • one horizontal cell synapses with 350-500 rods.

- There is a lot of convergence in the rod pathway.

28
Q

What do the golgi staining of flat mounted retinae show ?

A

how horizontal cells are ideally suited for mediating lateral interactions in the OPL
-ideally suited to mediate lateral interactions in the retina

29
Q

How is the lateral interactions mediated in the retina via horizontal cells via an illustration ?

A
  • cones that are distant from each other inhibit eachother
    -If a hyperpolarising current is injected into a cone, a depolarising current can be recorded from a more distant one
    -if we stimulate a cone with a small hyoerolarising current, you stimulate horizontal cell, which will take the info laterally and synapse with a more distant cone and then will inhibit that other cone cone on the right
    -so response you get in distant cone is the opposite of the current you injected on the right
    = this cone excites horizontal cell and the other cone inhibits
30
Q

What are horizontal cells responsible for?

A

for lateral interaction which enable one cone to inhibit a distant cone.
-helps increase contrast of adjacent objects

Neural Biology 1 (58 decks)

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