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Sem 3 Neuro > Case 3 > Flashcards

Case 3 Flashcards

1
Q

What is emmetropia?

A

Normal vision.

Light focuses directly on the retina.

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2
Q

What is myopia?

A

Nearsightedness.

Light focuses just in front of the retina.

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3
Q

What is astigmatism?

A

Refractive error where light fails to come to a single focus on the retina.

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4
Q

What is hyperopia?

A

Farsightedness.

Light focuses behind the retina.

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5
Q

What is strabismus?

A

The eyes do not properly align with each other when looking at an object.

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6
Q

What is esotropia?

A

Misalignment of eye(s) inward, (crosseyed)

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7
Q

What is exotropia?

A

Misalignment of eye(s) outward.

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8
Q

What is hypertropia?

A

Misalignment of eye(s) upward.

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9
Q

What is hypotropia?

A

Misalignment eye(s) downward.

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10
Q

Explain the sclera: What is it? What is it made of? What is its purpose?

A

Tough external covering of the eye.
Contains collagen fibres.
Protects and maintains the shape of the eyeball.

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11
Q

Explain the Cornea: What is it? What is it made of? What is its purpose?

A

Transparent anterior part of the sclera.

Its the curved surface acts as the main refractor of light towards the retina.

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12
Q

Explain the Ciliary muscles: What is it? What is it made of? What is its purpose?

A

Small muscles that come off of the ciliary bodies.
Made of smooth muscle.
Purpose is to tighten or slacken the LENS to change shape for focusing.

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13
Q

How do the ciliary muscles act in order to flatten or fatten the lens? Name the ligaments that they act on.

A

They are arranged around the circumference of the lens (i.e. they are circular).

When they contract - they pull inward, towards the lens, hence slackening suspensory ligaments. This causes the lens to get rounded (more fat).

When they relax - they pull outwards, away from the lens, hence tightening the suspensory ligaments. This causes the lens to get flatter.

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14
Q

To focus on something near, does the lens get rounded and fat, or tighter?

Briefly explain the changes of the suspensory ligaments and ciliary muscles that cause this to happen.

A

Near - fat lens.

The ciliary muscles contract, less tension on the suspensory ligaments.

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15
Q

To focus on something far, does the lens get rounded and fat, or tighter?

Briefly explain the changes of the suspensory ligaments and ciliary muscles that cause this to happen.

A

Far - tight.

The ciliary muscles relax, more tension on the suspensory ligaments.

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16
Q

Explain the Ciliary body: What is it? What is it made of? What is its purpose?

A

Part of the choroid (choroid root).
Produces aqueous humour (anterior chamber).
Contains the ciliary muscles.

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17
Q

Explain the suspensory ligaments: What are their purpose?

A

Attach the lens to the ciliary body.

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18
Q

Explain the lens: What is it? What is it made of? What is its purpose?

A

Transparent, elastic, biconvex structure.

Provides fine adjustment for focusing light on the retina.

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19
Q

What does accommodation mean (in terms of the eye, not living conditions lol).

A

Adjustment of lens (and pupil size) to focus light on the retina.

Remember the accommodation reflex in OSCE CN II test.

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20
Q

Explain the Iris: What is it? What is it made of? What is its purpose?

A

It is a muscular diaphragm containing pigment which gives the eyes in colour.
It controls the amount of light that enters the eye (size of pupil).

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21
Q

Explain the Pupil: What is it? What is it made of? What is its purpose?

A

Its a hole in the iris.

Purpose is to let light into the eye - to ultimately hit the retina.

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22
Q

What muscles cause pupil diameter to change? Name them and what each does.

A

Its diameter is changed based on the contraction of circular and radial muscles of the iris.

Circular muscle - contracts to make pupil smaller (i.e. smaller diameter).

Radial muscles - contract to make the pupil larger (i.e. larger diameter).

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23
Q

Explain the Retina: What is it? What is it made of? What is its purpose?

A

It is a light sensitive layer of tissue at the back of the eye.

Contains photoreceptor cells - Rods and Cones - and their associated neurones.

Essentially is a transducer. Transduction of light to an electrical impulse.

[take a focused 2D image of the visual world (light) and translate that into an electrical neural impulse (which can then be taken to the brain]

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24
Q

Explain the Fovea: What is it? What is it made of? What is its purpose?

A

Region of the retina, next to the optic nerve.

Made of only cone photoreceptors.

Purpose is to enable maximum discrimination of detail, as most light rays are focus here.

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25
Q

Explain the optic nerve: What is it? What is it made of? What is its purpose?

A

It is a nerve.
It is made of a bundle of nerve fibres.
Its purpose is to carry impulses from the retina to the brain.

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26
Q

Explain the blind spot: What is it? What is it made of? What is its purpose?

A

Its the point where the optic nerve leaves the eye.

Its where there are no photoreceptors (no rods or cones).

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27
Q

What is another name for the retinal ganglion cells axons.

A

Optic nerve

28
Q

When light enters the eye, name all the structures in passes before hitting the retina.

A 
Cornea.
Aqueous humour. 
Through pupil and iris. 
Lens.
Vitreous humour. 
Retina.
29
Q

Once light reaches the retina, name all the layers of cells it passes through before reaching the back of the eye.

A
  1. ganglion cell layer
  2. inner plexiform layer
    3 inner nuclear layer
  3. outer plexiform layer
  4. photoreceptor layer (first inner segment layer then outer segment layer).
30
Q

Do photons hit the opsin proteins first, or do they hit the photoreceptor synaptic ending first?

A

They hit the photoreceptor synaptic endings first.

31
Q

Where are the membranous discs of photoreceptors located (in terms of segments)?

A

Outer segment

32
Q

Which part of the photoreceptors absorb light?

A

opsin proteins

33
Q

What type of protein is an opsin protein?

A

GPCR (G protein coupled receptor)

34
Q

What is the co-factor that is bound to the opsin protein?

A

Retinaldehyde.

35
Q

What is Retinaldehyde derived from/ a derivative of?

A

Vitamin A

Carrots

36
Q

What structural change do photons cause to retinaldehyde (in the opsin protein).

Name the structure before, and after.

What is this structural change called?

A

11-cis retinal + light = all-trans retinal

isomerisation

37
Q

What affect does the isomerisation of retinal have on opsin?

A

It causes the activation of opsin protein, and thus the activation of the signalling cascade.

38
Q

What effect does opsin have on the spectral sensitivity of retinal? (Name what light wave is shifted)

How does it do this?

A

It shifts the spectral sensitivity of retinal from UV light to Visible light.

It does this through its Amino Acids.

39
Q

Does free retinaldehyde absorb light we can see?

Why?

A

no.
The wavelengths are too long/ frequencies too high.
It absorbs UV if free.

40
Q

Why can our genetics lead to variation in colour vision within the population?
e.g. colour blindness.

A

Our genetics determine the amino acids on opsin proteins (on photoreceptors).

These amino acids are what effects the spectral sensitivity shift of retinal.

They set retinaldehyde absorbance.

41
Q

How many cones are there and what colours are they sensitive to?

A

3 cones

Red, Blue, Green

42
Q

In terms of GPCR’s, what molecule can 11-cis retinal be considered as?

A

A Ligand

43
Q

When bound, what effect does 11-cis retinal have on opsin?

What is this known as?

A

Keeps opsin inactive.

“Inverse agonist”

44
Q

What is photo-isomerisation with regards to retinal?

A

A structural change from 11-cis to all-trans retinal caused by photons.

45
Q

What does photo-isomerisation to all-trans retinal, and dissociation of retinal, cause?

A

Triggers an intracellular signal via opsin protein.

46
Q

Go through the 4 step signalling cascade that happens with opsin (signal cascade)

A
  1. Rhodopsin is activated with photon.
  2. Active rhodopsin binds to and dissociates “transducens” (G protein).
  3. Activated alpha subunit now binds to enzyme PDE (phosphodiesterase). PDE decreases cGMP nearby.
  4. cGMP conc. decrease causes channel closure.
47
Q

Are cGMP channels usually open or close? (with no light)

A

They are usually open.

48
Q

What does the constant open cGMP channels of photoreceptors result in? How does this affect cell activity?
Does it change in the light or in the dark?

A

It results in a constant influx of Na+.

This results in constant activation of the photoreceptor.

49
Q

How are the cGMP channels affected by:
1) the light and
2) the dark?
(think Na+)

What affect do they have on photoreceptor cell activity?

A

The light - the cGMP gates close. The Na+ stops entering, ergo the cell stops depolarising - no activity. “Switched off by light”

The dark - the cGMP gates are open. The Na+ continues to enter, ergo the cell is constantly depolarising.

50
Q

What Neurotransmitter is released by the photoreceptors? which layer does this happen in?

A

Glutamate.

Outer plexiform layer.

51
Q

Where on the retina are cones most concentrated?

A

Fovea

52
Q

Which (rods or cones) are used for light and dark vision?

A

Rods - dark vision

Cones - light vision

53
Q

Why does focusing light on the fovea give us best visual acuity?

A

Because there are only cones present.

Cones enable better discrimination - due to more direct connections to ganglion cells.

54
Q

Are cones or rods more sensitive? explain.

A

Rods are more sensitive, because:

  1. Capture more photons
  2. Have a larger signal amplification

There is also an effect of “summation”, because many rods can synapse to a single bipolar cell.

55
Q

Which provide colour vision, rods or cones?

A

Cones

56
Q

What do bipolar cells synapse with on the outer plexiform layer?

A

Photoreceptors

57
Q

What do bipolar cells synapse with on the inner plexiform layer?

A

Ganglion cells

58
Q

What cells are involved in the lateral pathway in the outer plexiform layer? What do they do?

A

Horizontal cells.
They collect information from photoreceptors.
They add up the impulses and help broaden the receptive field.

59
Q

What do amacrine cells do? and which layer are they found in?

A

They link rod bipolar cells to cone bipolar cells.
They merge them on one ganglion cell.
Found on inner plexiform layer.

60
Q

What do bipolar cells do generally?

A

They connect (usually multiple) photoreceptors to ganglion cells.

61
Q

The optic chiasm contains nerve fibres crossing from which aide of the retina? Nasal or Temporal?

A

Nasal.

62
Q

Where do the optic tracts terminate?

A

Lateral geniculate nucleus.

63
Q

What is the loop in the optic radiation called? Where does enter?

A

Meyers loop. It enters the temporal lobe before passing posteriorly.

64
Q

Name the four subcortical regions in the brain which the retina projects to.

Group them into the primary visual pathway(s) and the secondary visual pathway(s).

A

Primary visual pathway:
1. Lateral Geniculate nucleus (LGN)

Secondary visual pathway:

  1. Superior colliculus/colliculi
  2. Hypothalamus
  3. Pretectum
65
Q

What are the secondary visual pathway subcortical regions responsible for?

  1. Superior colliculi
  2. Hypothalamus
  3. Pretectum
A
  1. Superior colliculi - Pupil responses, eye movements
  2. Hypothalamus - Circadian rhythm
  3. Pretectum - Pupil responses
66
Q

Describe the pupil light response pathway: starting from the light shining into eye, and ending with pupil constriction.

A
  1. optic nerve
  2. Superior culliculus
  3. Pretectal nucleus
  4. Edinger-westphal nucleus
  5. Oculomotor nerve CN III
  6. Ciliary ganglion
  7. Short ciliary nerve
  8. circular muscle of iris

Sem 3 Neuro (8 decks)

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