Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Neurophysiology > Vision > Flashcards

Vision Flashcards

1
Q

What side of the retina do the temporal and nasal visual fields focus on?

A

The temporal visual field focuses on the nasal part of the retina.

The nasal visual field focuses on the temporal part of the retina.

This is because the optics of the eye invert the image.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Give the Specific features of an eye.

A

Needs:

  • stable shape
  • ability to focus image
  • transmit the image to visual cortex
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What gives the eye its shape?

A

Outer fibrous layer:

  • sclera
  • cornea

Inner:

  • aqueous humour
  • vitreous humour
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the Sclera?

A

white non-stretchy layer creating the anchoring point for ocular muscles, keeping the eye rigid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the role of the Cornea in the eye shape?

A

collagen fibres align in a way to make the outer fibrous layer transparent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the role of the Aqueous humour in the eye shape?

A

fluid produced by the ciliary body which flows outwards (front of eye) and is eventually reabsorbed through the angle of the eye

it is the balance between production and reabsorption/drainage which generates intraocular pressure keeping the sclera rigid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the role of the Vitreous humour in the eye shape?

A

jelly-like fluid behind the lens, hydrated by aqueous humour, that maintains shape of eye and keeps it transparent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What gives the eye the ability to focus an image?

A

Optics:

  • cornea
  • lens
  • ciliary body
  • iris
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the role of the cornea in focus?

A

bends light rays to bring them back to a single point as part of the focusing of the image

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the role of the lens in the eyt shape?

A

transparent structure that changes shape to provide variable fine focus of the eye

*suspended by ring of suspensory ligaments from ciliary body

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the role of the Ciliary Body in focus?

A

contains a ring of muscle which changes shape of lens by contracting or relaxing:

  • contracts to fatten lens for close vision (decreased diameter)
  • relaxes to flatten lens for distance vision (increased diameter)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the role of the Iris in focus?

A

ring of muscle which creates coloured part of the eye

controls diameter of aperture (pupil), controlling how much light eyes the eye via the pupil
-the smaller the aperture, the better the focus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

When does the pupil dilate?

A

dim light to let enough light to give a bright enough image

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What structure transmits light information to the brain?

A

Retina

> Neural retina: contains photoreceptors and afferent retinal ganglion cells which have the axons that run across the surface of the retina and form the optic nerve

> Retinal pigment epithelium: provides a lot of biochemical support for the photoreceptors and also holds the retina in place, preventing it from peeling away

> Optic nerve: central nervous system tract myelinated by oligodendrocytes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How does the eye transmit image/light to the visual cortex?

A

Primary Visual Pathway:

1) The retinal ganglion cell axons project down the optic nerve to the optic chiasm, and at the optic chiasm, the ones on the nasal half of the retina swap sides. The axons from the temporal half of the retina stay on the same side.
2) They project back to the lateral geniculate nucleus (LGN) in the thalamus.
3) Cells in the lateral geniculate nucleus send their axons through a region of white matter known as the optic radiation back to the occipital cortex, where the primary visual area is located.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is phototransduction?

A

The conversion of light into electrical signals in the rods, cones and photosensitive ganglion cells of the retina of the eye

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are photoreceptors?

A

specialised cells in retina which respond to light:

Rods- night vision
Cones- day vision

*most of the time the cones are being used

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Describe the Cone photoreceptor structure.

A

> Inner Segment: nucleus and protein-making machinery etc.

> Outer Segment: bag containing tightly packed layers of phospholipid membrane which hold the chromophore (light sensitive molecule) perpendicular to the light path, ensuring efficient trapping of light rays

> Axon: not really an axon, just a neurite, as it doesn’t fire action potentials, and doesn’t need to because it is a very small cell and can transmit information via electrotonic potentials

> Synaptic Terminal: releases glutamate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Describe the Electrophysiology of cone photoreceptor at rest.

A

· Photoreceptor nerve cells leak K+ all the time, producing a negative internal potential, resulting in a resting membrane potential of -45mV (more depolarised than normal membrane potential -70mV).
· These cells are depolarised even at rest due to Na+ channels in the outer segment being open by default, allowing for the influx of Na+, and there is also glutamate being released from synaptic terminal
· Glutamate, though usually excitatory, functions here as an inhibitory neurotransmitter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Describe the Electrophysiology of cone photoreceptor in response to increased light.

A

· If the light striking the outer segment gets brighter, some of the Na+ channels close, causing the cells to become more negative inside (hyperpolarisation) as there is no more Na+ influx

·This prevents the release of inhibitory glutamate from the synaptic terminals, sending a signal along the visual pathway

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Describe the Electrophysiology of cone photoreceptor in response to decreased light.

A

· If the region striking the outer segment gets darker, more Na+ channels open, allowing for the influx of Na+ and depolarising the cell

· More glutamate is released from synaptic terminal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What holds Na+ channels open in photoreceptors?

A

cGMP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Describe the structure of Photopigment in cones.

A

photopigment on membrane disc made of:

  • opsin protein
  • light sensitive chromophore called retinal (11-cis retinaldehyde)
24
Q

Describe the Structure of 11-cis retinaldehyde.

A

made up of a carbon ring and a carbon tail

All of the carbon-carbon links that make the tail are in the trans-configuration except for one in the 11th location, which is in the cis-configuration.

The cis-configuration is less stable than the trans-configuration.

25
Q

Describe the Transduction reaction when light strikes photopigment in cones.

A

1) Unstable 11-cis bond in retinal ruptures and reforms in the more stable trans-configuration, resulting in all-trans retinaldehyde
2) Opsin is now linked to all-trans retinaldehyde and the photopigment is now activated, and behaves in the same way that a G-protein coupled receptor would behave when activated
3) A single activated photopigment can activate many G-proteins, and each of those activated G-proteins go on to activate the enzyme responsible for destroying cGMP
4) There is a fall in intracellular cGMP, and cGMP diffuses away from the Na+ channels on the membrane, closing the Na+ channels

26
Q

Describe the Transduction reaction when there is termination of the light response.

A

1) Activated photopigment is capped and retinal removed
2) G-proteins are not activated and therefore the enzymes which break down cGMP are not activated either
3) This allows a second enzyme to restore cGMP levels, which reopens the Na+ channels
4) Another molecule of 11-cis retinaldehyde is attached to the opsin, ready to respond to the next incoming photon

27
Q

Why are cones able to produce a big response to a very small change in illumination?

A

due to the amplifying cascade after each photon activates a photopigment, subsequently activating lots of G-proteins which activate the enzyme that produces a rapid change in cGMP

28
Q

Which structure allows you to see detail?

A

small part of the retina called the fovea centralis allows you to see in detail with the very centre of your visual field

29
Q

What causes loss of peripheral vision?

A

· If you have a disease attacking the peripheral retina (e.g. glaucoma, retinitis pigmentosa), peripheral vision is lost, however the central visual field which allows you to see in detail is undestroyed and kept for a long time until quite later in the disease process.

30
Q

What causes loss of central vision?

A

· If you have a disease attacking the central retina (e.g. age-related macular degeneration), central vision is lost, and you lose the ability to see in detail. Someone who has lost that tiny bit of their visual field, even though the rest of their vision is intact, will still be registered blind because although they may be able to navigate through the world, they won’t be able to recognise faces or read. Therefore, the central retina is hugely important.

31
Q

Describe the Structure of peripheral retina.

A

10x as many rods as cones, therefore cones are separated by a pool of rods, making big gaps in the sampling array

32
Q

What do ganglion cells in the peripheral retina receive input from? And how?

A

Receive input from photoreceptors via bipolar (interneurone) cells, which pick up input from a whole pool of photoreceptors after convergence of signals from different photoreceptors

33
Q

What is the Ganglion’s receptive field centre?

A

part of the visual world directly linked to the ganglion cell

*bigger receptive field centre= less fine details

34
Q

Why does the peripheral retina not provide good focus?

A

because the light is scattered en route to the outer segment of photoreceptors due to the dense capillary beds and nuclei/organelles of cells it has to pass through, therefore image blurs as light passes through retinal tissue

35
Q

Where is the central retina located and what does it contain?

A

within the optic nerve head containing a dark structure called the fovea centralis

36
Q

What is the Foveal pit?

A

region composed of closely packed small cones (not spaced and no rods) and there is no inner retinal tissue between them and light path, therefore there is no image blur and there is fine focus

37
Q

Which coloured cones are in the central retina and why?

A

only red and green cones in this region (no blue cones) because only red and green cones are associated with the circuitry that puts out fine detail

38
Q

What do ganglion cells in the central retina receive input from?

A

receive input from a single cone photoreceptor, meaning there is no convergence

this signal from the fine sampling array (tight cones) remains uncontaminated all the way back to the primary visual cortex

39
Q

Describe Peripheral Vision.

A

Majority of the retina outside of the foveal pit serves only coarse vision:

· The visual image is optically blurred

· The cone photoreceptors are large and widely spaced (separated by larger number of rods)

· The signals from many cones converge onto single ganglion cells via bipolar cells

· Poor vision

40
Q

Describe Central Vision.

A

The fovea in the central retina is specialised for high resolution:

· Good focus- overlying retinal layers are absent

· Only cone photoreceptors- primarily red and green- are narrow and closely packed

· The signals from the photoreceptors are kept separate throughout the primary visual pathway and there is no convergence

· Fine detailed vision

41
Q

Right hand side of the image is focused onto what side of both retina? And what side of the brain do they send information back to?

A

left hand side of both retina, sending information to left side of brain

42
Q

Left hand side of the image is focused onto what side of both retina?

A

right hand side, sending information to right side of the brain

43
Q

What is the Location of red, blue and green cone photoreceptors in the retina?

A

cones in the middle are more closely packed and are only red and green (for fine focus), indicating that the middle area is the foveal pit

cones further out are more spaced apart with all three colours

44
Q

Describe the Adaptation to light.

A

after photoreceptor responds to an increase in light, there is adaptation if the eyes stay in that same location for a length of time:

the brightness doesn’t change and the photoreceptor adapts and resets itself by going back to its resting potential. Now the photoreceptor is ready to respond to another change in brightness. This can happen over an enormous range of absolute illuminations.

Over the whole of this range, our photoreceptors are able to respond very sensitively to tiny changes in brightness very quickly without saturation because they constantly reset their membrane potentials through “adaptation”.

45
Q

what is Lateral Inhibition in the Retina?

A

The reduction of activity in one neurone by activity in neighbouring neurones

Central retinal ganglion cell receiving excitatory input from single cone, but also inhibitory input from cones surrounding that one signal cone

The response of cells in the visual system depends upon the net result of excitatory and inhibitory signals it receives:
>If light decreases over the central cone, the cone becomes depolarised, subsequently depolarising the bipolar cell, and then depolarising the ganglion cell
>If light decreases over a surrounding cone, it will depolarise the inhibitory interneuron which will inhibit the bipolar cell and the ganglion cell

46
Q

How does brightness in the central receptive field and surrounding inhibitory receptive field affect ganglion cell response?

A

If the brightness in the central receptive field and the surrounding inhibitory receptive field is different, then the excitation and inhibition won’t cancel out and the ganglion cell will respond.

If the brightness in the central receptive field and the surrounding inhibitory receptive is the same, then the excitation and inhibition will cancel out and the ganglion cell will not respond.

47
Q

What do retinal ganglion cells respond to?

A

half respond to increases in illumination

half respond to decreases in illumination

48
Q

How do retinal ganglion cells respond to increases in illumination given that all photoreceptors are depolarised by decreases in illumination?

A

“on” central retinal ganglion cells coming from the central cone photoreceptor has an inverting synapse
-therefore, when the cone photoreceptor hyperpolarises to an increase in illumination, the inverting synapse depolarises bipolar cell, which excites the ganglion cell

49
Q

What are the main classes of retinal ganglion cells?

A

magnocellular and parvocellular retinal ganglion cells at each point in the retina

50
Q

What are Magnocellular retinal ganglion cells?

A

> pool of cells which are very sensitive and designed to respond to fast moving things, but they do so at the expense of being no good at seeing fine details
more convergence for coarse resolution

51
Q

What are Parvocellular retinal ganglion cells?

A

> pool of cells designed to pick up fine detail, but they are not very sensitive because they get very little input.

52
Q

Which retinal ganglion cells are wavelength selective?

A

Parvocellular

  • receive inputs from red and green photoreceptors
  • encode wavelength by comparing responses from these inputs

Bistratified

  • receive inputs from blue or “red+green=yellow” photoreceptors
  • encode wavelength by comparing responses from these inputs

*these comparisons are the basis of colour vision

53
Q

Give the Comparison between LGN receptive fields and retinal receptive fields.

A

> Lateral geniculate cells are pretty faithful relay cells- their receptive fields look like those of their retinal inputs (e.g. parvocellular, magnocellular, off centre, on centre etc.)

54
Q

How do primary visual cortical cells respond to changes in brightness?

A

each point in visual space focuses onto adjacent points in the retina, and the adjacent points project back to adjacent points in the cortex

they have more elongated receptive fields than the retina and they don’t just respond to contrast, but to contrast in a specific direction (orientation sensitive)

Therefore, it is very difficult to get primary visual cortical cells to respond to vision because they are very specific about what they respond to, but that also means that their response has meaning because when they respond and fire action potentials, it means something very specific is going on in the retinal picture.

55
Q

What is the Primary Visual Cortex Input Distribution?

A

Inferotemporal Visual Areas

  • encode information about object identity
  • receive input from parvocellular cells

Cortical Areas
-process colour

Parietal Visual Areas

  • encode information about location and movement
  • receive input from magnocellular neurones (don’t need fine detail)

Neurophysiology (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions