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Week 130 - Sudden Visual Disturbance > Retinal Function and Visual Pathways > Flashcards

Retinal Function and Visual Pathways Flashcards

1
Q

Describe a photoreceptor at rest (in the dark)

A

Become depolarised (Na+ diffusing in, Ca2+ pumped out, cyclicGMP keeps Na+ gate open)

Producing Glutamate

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2
Q

Describe photoreceptors in light?

A

Cell hyperpolarises i.e. become more -ve than outside

Reduction in glutamate production

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3
Q

How do photoreceptor cells hyperpolarise in light?

A

Photon hits rhodopsin molecule causing retinal dissociation, i.e. small retinal molecule to change shape and dissociate from large opsin molecule

Retinal molecule inactivates cGMP so that Na+ gates close, i.e. Na+ can’t get in but Ca2+ still pumped out

Results in cells becoming negative

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4
Q

What occurs in the neural processing of diffuse light?

A

Lateral inhibition by horizonal and amacrine cells limits depolarisation of photoreceptors and impulses sent if diffuse light hitting large area of retina

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5
Q

What is the nerve fibre layer made up of and where in the eye will you find it?

A

Nervous ganglia nuclei

Overlying the retina

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6
Q

Explain the role of ganglia in the nerve fibre layer

A

Nervous nuclei and fibres which lead to the optic disc

Approx. 2% are photosensitive to blue light

They also regulate melatonin production for circadian rhythms

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7
Q

What is the role of the inner plexiform layer?

A

Synapses between ganglia and bipolar/amacrine cells

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8
Q

What processor and supportive cells make up the inner nuclear layer?

A

Processor cells - horizontal and amacrine cells

Supportive cells - Muller cells

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9
Q

What is the role of bipolar cells in the nuclear layer?

A

Relay impulses from photoreceptors to ganglia

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10
Q

What is the role of amacrine cells in the nuclear layer?

A

Laterally inhibit photoreceptors and ganglia

Mechanism of action is unknown

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11
Q

What is the role of muller cells in the inner nuclear layer?

A

Muller cells are glial cells (nervous connective tissue cells) therefore act as support cells.

Also shown to differentiate into progenitor cells in response to retinal damage

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12
Q

What is the role of the outer plexiform layer?

A

Synapses between photoreceptors and processor cells

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13
Q

Where is the photoreceptor layer and what is it composed of?

A

Outer nuclear layer, made up of rods (~120m) and cones (~7m) which are concentrated in the fovea

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14
Q

What are the roles of rods and cones in the photoreceptor layer?

A

Rods - sense light/darkness

Cones - sense red and green or blue

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15
Q

How is light transferred into a nervous impulse?

A

Rods and cones contain rhodopsin, light (photons) causes hyperpolarisation by break down of rhodopsin into large opsin and small retinal molecules, retinal molecule inactivates cGMP molecule and closes NA gate, Ca2+ pumped out Na+ cant get in, cell becomes -ve and reduced glutamate production, this signal reaches ganglia and is then transmitted to the optic nerve.

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16
Q

What is the role of the retinal pigment epithelium?

A

Prevents reflection of light and phagocytoses cell debris from inner layers

17
Q

What is the choroid?

A

Vascular supply of the retina but on a seperate layer

18
Q

How does the action of bipolar centres affect vision?

A

One bipolar cell connects to many rods.
If centred on a hyperpolarising rod, the bipolar cell will depolarise.

However this is inhibited by horizontal and amacrine cells when a bipolar cell is neighboured by a non hyperpolarising rod.

This allows for increased edge/contour definition.

19
Q

How do bipolar cells affect foveal acuity?

A

One cone is connected to one bipolar cell therefore acuity is increased?

20
Q

How does colour blindeness occur?

A

Red, blue and green cone cells each have different rhodopsin molecules.
Colour blindness occurs when the eye is unable to produce one of these rhodopsin molecules.
Most commonly red and green, this is a sex linked condition therefore most common in boys

21
Q

What stimuli will make the pupils change in size?

A

Change in light/dark and close/distant objects

22
Q

Describe the pathway of the pupillary light reflex?

A 
Optic nerve -> 
optic chiasm -> 
pretectal nuclei -> 
erdinger westphal nuclei ->
occulomotor nerve/ciliary ganglia/constrictor muscles of iris
23
Q

Why do both eyes respond to a light stimulus in one eye?

A

In the optic chiasm, fibres from the medial half of the retina decussate whilst fibres from the lateral half remain ipsilateral (same side)

24
Q

What would a lesion to the optic nerve anterior to the optic chiasm result in?

A

No sensory information passing from that eye

25
Q

What pupillary effect would a lesion to the optic nerve begind the optic chiasm result in?

A

Will not affect the pupillary light reflex as fibres from the other eye will pass to both erdinger westphal nuclei

26
Q

What pupillary effect would a lesion to an occulomotor nerve result in?

A

Prevent any response in that eye but have no effect on the other

27
Q

What are the three actions of the pupillary near response?

A

Convergence, accomodation, and constriction

28
Q

Describe the sensory pathway?

A 
Optic nerve ->
optic chiasm ->
lateral geniculate bodies ->
optic radiations ->
primary visual cortex
29
Q

What occurs in the sensory pathway at the optic chiasm?

A

Fibres from medial half of retina (or lateral visual field) decussate

fibres from lateral half remain on ipsilateral field

30
Q

Where are the lateral geniculate bodies found?

A

Thalamus

31
Q

What occurs in the sensory pathway at the lateral geniculate bodies?

A

Fibres synapse and split into those from top and bottom of retina

32
Q

What does the superior optic radiation carry and to where?

A

Carry fibres from upper retina (lower field of vision) through the parietal lobes

33
Q

What does the inferior optic radiation carry and to where?

A

Carries fibres from the lower retina (upper field of vision) through the temporal lobes

34
Q

What occurs at the visual cortex and where is it?

A

Neurons from radiations synapse with corticol cells

In the occipital lobe

35
Q

What is macular sparing and why does it occur?

A

Poor blood supply to the cortex makes it vulnerable to CVA

However, cells dealing with macula located at the occipital pole dual blood supply, therefore can be spared in CVA

36
Q

Describe the motor pathway

A

Visual cortex->
frontal eye field ->
erdinger westphal nuclei ->
occulomotor nerve

37
Q

What would a central lesion in the optic chiasm result in?

A

Bitemporal hemianopsia (blindness over half vision field)

Week 130 - Sudden Visual Disturbance (4 decks)

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