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SGUL - Physiology 2 > Vision > Flashcards

Vision Flashcards

1
Q

How does the optic nerve travel through the eye?

A

Travels Nasally

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2
Q

What is the structure of the eye?

A

Has an outer fibrous layer containing
- Sclera: Quite flexible
- Cornea: The transparent bit of the eye

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3
Q

How is the sclera flexible?

A
  • To do this, it need an element which holds it rigid
  • This is done by providing a certain amount of intraocular pressure
  • Pressure generated through the production of aqueous humor
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4
Q

How is the flexibility of the sclera maintained?

A

As long as the production and drainage in balance properly, it will produce just enough pressure in your eye to keep it rigid

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5
Q

What are the optics of the eye?

A
  • Cornea
  • Lens
  • Both bend light
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6
Q

What is one feature about the Cornea and the lens?

A
  • The Cornea bends the light rays inwards to the eye
  • The lens can change shape in order to change the focus of the eye
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7
Q

What supports the lens to help keep it in place?

A

The lens is held in place by a ring of suspenseful ligaments from the ciliary body

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8
Q

What can the ciliary body do to the lens?

A

Can change the shape of the lens as it’s a ring of muscle, when it contracts, it’s diameter becomes smaller causing the lens to become fatter.

When relaxed, it becomes wider, diameter becomes larger flattening the lens for distance vision

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9
Q

What is the iris part of the eye?

A

The ring of muscle which Creates the colour part of the eye
- Function: Produces an Aperture in the middle known as the pupil
- Maintains the smallest aperture it can for the illumination conditions
- The smaller the aperture, the better the focus conditions

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10
Q

What happens with the retina indifferent lights

A

Adjusts the eye based on brightness
- Becomes larger in a dim lighted area
- Becomes narrower in bright sunlight

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11
Q

Describe what happens when light touches the eye?

A
  • Some photons strike the cornea and pass through
  • Some are stopped by the iris
  • Those which pass through the pupil will be bought to a single point for focus by the cornea and the lens
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12
Q

What are the key elements of the eye when under the sunlight?

A
  • The cornea is the most powerful refractive surface of our eye
  • The lens provides additional variable fine focus
  • The iris controls how much light enters the eye via the pupil
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13
Q

Where is the retina found?

A

Found at the back of the eye

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14
Q

What are the two parts of the retina?

A
  • Neural retina
  • Retinal pigment epithelium: Provides a lot of support for photoreceptors. Also holds the retina in place
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15
Q

Where was the retinal pigment epithelium developed

A
  • Developed embryonically from the neural tube
  • This means because they both came from the neural tube, they’re both CNS structures
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16
Q

What is special about the retina?

A
  • Holds basically the whole massive surface of the eye
  • Technically apart of the brain
  • Has photoreceptors
  • Also has Afferens which are retinal ganglion cells
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17
Q

What do the retinal ganglion cells have?

A
  • Have axons which run across the surface of the retina which form the optic nerve
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18
Q

Describe the Primary visual pathway (PART 1)

A
  • The ganglion cell axons project down the optic nerve to the optic chiasm
  • One on the nasal part of the retina swap sides however those from the temporal sides stay on the same side
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19
Q

Describe the Primary visual pathway (PART 2)

A

They then project back to the lateral geniculate nucleus which serves the visual system
- Cells in this region then send their axons through a region of white matter known as optic radiation
- Back to the opsiticsl cortex where you find the primary visual area

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20
Q

What are the two forms which photoreceptors come in?

A
  • Rod photoreceptors: Night vision
  • Cone Photoreceptors: Day vision
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21
Q

What is the similarities & difference between rods and cones?

A
  • They use the same neural circuitry
  • But at the retina, you’ve either got rods and their circuitry or cones and their circuitry
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22
Q

How do the rods become react to the level of light overtime?

A
  • They become super sensitive since they’ve had a lot of time to react
  • This allows you to see a lot more clearly in the dark
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23
Q

Describe the structure of the cones photoreceptors

A

Has an outer and an inner segment
Contains
- A membrane disc
- Nucleus
- Axon
- Synaptic terminal

24
Q

What does the inner segment contain?

A

Contains the nucleus as well as the replication machinery

25
Q

What does the outer segment contain?

A

Contains the transduction mechanism
- A bag of tightly packed layers containing phospholipid layers

26
Q

What is the resting membrane potential in cone photoreceptors?

A

-45 mV

27
Q

What does this mean about the membrane potentials?

A
  • Meaning they’re depolarised even at rest
  • This is due to in the outer segment there are sodium channels which are open by default
28
Q

What is the cones photoreceptors response to darker light?

A
  • When the light gets darker
  • More Na+ channels open depolarising the cell
  • Causing it to release more glutamate
29
Q

What is the cones photoreceptors response to brighter light?

A

Does the opposite
- Releases less glutamate

30
Q

What’s the difference between 11-cis retinaldehyde and the trans conformation?

A

The cis one is less stable

31
Q

Where is 11 cis retinaldehyde found?

A
  • In the membrane disc which is found in the outer segment
  • There is ops in which contains a cis retinal
32
Q

What happens when light touches the 11 cis retinaldehyde?

A
  • Causes the unstable bond to rupture
  • When it reforms, it reforms in the more stable trans configuration
  • This forms a trans retinal containing an all trans retinaldehyde
  • The opsin behaves in the same way a G protein linked receptor would behave when it’s activated
33
Q

What occurs next when light touches this molecule?

A
  • Activates a G protein which then activates many other G proteins
  • Each G protein go onto activate an enzyme
  • These enzymes destroy cGMP
  • You get a fall in the level of cGMP intracellular
  • Causes some cGMP to diffuse away from its channel and allows them to close
34
Q

How long are these G proteins activated for?

A
  • They’re only activated very briefly
35
Q

How are the cGMP levels restored?

A
  • When the G proteins are inactivated, a second enzyme comes along
  • Allowing to rebuild the cGMP levels which reopens those channels
36
Q

When do you lose your visual field?

A
  • If you have a disease attacking the peripheral retina like glaucoma or retinitis pigmentosa
  • You’ll lose some visual field
37
Q

When do you lose the central vision?

A
  • Something like age related macular generation
  • This goes for the central retina and destroys it
  • You won’t be able to see the centre of your vision but will be able to see the surrounding bits
  • This person will then be registered as blind
38
Q

What does the cross section of the through peripheral retina contain?

A
  • Pigment epithelium
  • Photoreceptors
  • Interneurons
  • Ganglion cells
39
Q

What happens to the image as it passes through the retinal tissue?

A

The image blurs as light passes through retinal tissue

40
Q

What is the central retina called?
Where is it found?

A
  • Called the fovea centralis
  • Found at the back of the eye/retina
  • No blood vessels go over it
41
Q

Describe the foveal centralis

A
  • Has a fovea (1.5 mm)
  • Has a foveal pit (0.35mm)
42
Q

What is the foveal pit?

A

The region where the photoreceptors are uncovered
- There is no retina sitting in between them and the light path
- So there in no blur
- You’ll have very excellent sampling as there’s no rods but the cones are packed closely together

43
Q

Describe the peripheral vision

A

Majority of the retina serves only coarse vision
- The visual image is optically blurred
- The cone photoreceptors are large and widely spaced (Separated by larger numbers of rods)
- The signals from many cones converge onto single ganglion cells

44
Q

Describe central vision

A

The fovea is specialised for high resolution
- Good focus
- Only cone photoreceptors, primarily red and Green
- Which are narrow and closely packed
- The signals from the photoreceptors are kept separate throughout the primary visual pathway

45
Q

Which part of the brain deals with vision?

A

The right hand side of the brain looks at the left hand side of the visual world through both eyes

46
Q

How does the retinal circuitry work?

A
  • It is designed to pull out changes in brightness from one place to the neighbouring place
  • It does this by lateral inhibition
47
Q

What does the retinal ganglion cells report?

A
  • Changes in illumination from one location to another
48
Q

What do retinal ganglion cells respond to?

A

Half of all retinal ganglion cells respond to increase in brightness

49
Q

How do they respond to a decrease in brightness?

A
  • Central photoreceptors depolarised (red) by decreased illumination
  • Bipolar and ganglion cells depolarised by excitatory synapses
50
Q

How do they respond to a increase in brightness?

A
  • Central photoreceptor hyperpolarised (blue) by increased illumination
  • Bipolar cell depolarised by inverting synapse, excites ganglion cell
51
Q

Which two classes can retinal ganglion cells be divided into?

A
  • Parvocellular
  • Magnocellular
52
Q

Describe the Parvocellular divison

A
  • Small field with strong surround
  • Fine resolution
  • Accurately follows changes in light
  • Needs stable image
53
Q

Describe the magnocellular division

A
  • Large field with weak surround
  • Coarse resolution
  • Transcient responses to changes
  • Responds well to fast movement
54
Q

Where do the Parvocellular cells get their inputs from?

A
  • Selective inputs from the red or Green photoreceptors
  • By comparing these responses they can encode wavelengths
  • Red vs wavelength
55
Q

Describe the bistratified input

A
  • Selective inputs from blue or red+green photoreceptors
  • By comparing these responses they can encode wavelength
  • Blue vs yellow

SGUL - Physiology 2 (37 decks)

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