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Unit 14 Week 1 > neurobiology of vision > Flashcards

neurobiology of vision Flashcards

1
Q

action of the brain lobes in relation to vision

  1. occipital
  2. parietal
  3. temporal
  4. frontal
A
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2
Q

what is and role of retina

A

membrane on the inner aspect of the eye that contains photoreceptors

made up of multiple layers

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3
Q

pupil

A
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4
Q

lens

A

transparent section behind the pupil that is enclosed in a thin transparent capsule

can be changed shape to help focus/refract light onto the retina by having its shape changed by the ciliary muscle

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5
Q

choroid

A

middle layer of the eye between the retina and the sclera

contains a pigment that absorbs excess light, preventing blurring of vision

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6
Q

ciliary muscle

A

a ring of smooth muscle in the eye’s middle layer (vascular layer) that controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humor into Schlemm’s canal.

links the choroid layer to the iris

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7
Q

macula

A

small yellow spot on the retina at the back of the eye.

surrounds the fovea

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8
Q

fovea

A

small indentation at the very back of the eye

thin so light can more directly reach photoreceptors

composed of closely packed cones

low ratio between cones and ganglion cells, high resolution abd gives us our best acuity

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9
Q

optic nerve

A

CN II carrying sensory info from thre retinal ganglion cells to the brain, syanpsing in the LGN

where it joins the retina there are no photoreceptors, giving us an anatomical blind spot

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10
Q

sclera

A

tough protective layer that covers the eye- the cornea is an anterior projection

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11
Q

iris

A

regulates the amount of light that can enter the eye

coloured part in fornt of the lens

night enters through it via the pupil

allows for dilation and constrictiuon of the pupil

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12
Q

which 2 structures focus light via refraction onto the retina

A

cornea and lens

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13
Q

anterior cavity

A

space between cornea and lens

filled with watery substance known as aqeous humor

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14
Q

posterior cavity

A

space behind the lens

filled with vitrous humor

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15
Q

the retina is made up of which 2 kinds of photoreceptor

what is the name of the pigments that absorb light

A

cone cells

  • Fewer in number
  • conical shaped
  • low sensitivity to light
  • responsible for colour vision
  • localised at fovea

rod cells

  • More abundant
  • cylindrical shaped
  • high sensitivity to ligh
  • function in night vision
  • low visual acuity
  • absent at the fovea.

contain an inner segment within which there are normal organelles

outer segment is specialised for photoreception containing rhodopsins

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16
Q

layers and their cells of the retina (3)

A

1) outer plexiform layer- includes photreceptors
2) inner plexiform- contains bipolar cells, horizontal cells and amacrine cells
3) ganglion cell layer- contains ganglia cells

17
Q

horizontal cells

A
  • forms synapses with bipolar cells and photoreceptor cells
  • laterally interconnecting neurons having cell bodies in the inner nuclear layer of the retina
  • help integrate and regulate the input from multiple photoreceptor cells
18
Q

bipolar cells

what is their role in phototransduction

A

exist between photoreceptors and ganglion cells

They act, directly or indirectly, to transmit signals from the photoreceptors to the ganglion cells.

In the dark, a photoreceptor (rod/cone) cell will release glutamate, which inhibits (hyperpolarizes) the ON bipolar cells and excites (depolarizes) the OFF bipolar cells. In light, however, light strikes the photoreceptor which causes the photoreceptor to be inhibited (hyperpolarized) due to the activation of opsins which activate All trans-Retinal, giving energy to stimulate G-Protein coupled receptors to activate phosphodiesterase (PDE) which cleaves cGMP into 5’-GMP.

19
Q

how do photoreceptors link to ON and OFF bipolar cells

A

In the dark, a photoreceptor (rod/cone) cell will release glutamate, which inhibits (hyperpolarizes) the ON bipolar cells and excites (depolarizes) the OFF bipolar cells.

In light, however, light strikes the photoreceptor which causes the photoreceptor to be inhibited (hyperpolarized) due to the activation of opsins which activate All trans-Retinal, giving energy to stimulate G-Protein coupled receptors to activate phosphodiesterase (PDE) which cleaves cGMP into 5’-GMP.

20
Q

amacrine cell

A

interneurone in the retina that allows ganglia to send temporarily correlated signals to the brain

21
Q

what kind of molecules capture photons

there are different kinds of these in rods and cones, name them (1 rod and 3 cones)

in cones, one type of ospin usually predominates

in colour blindness the red/ green opsins in cones can be swapped around

A

pigment molecules

22
Q

receptor potentials in photoreceptors

A
23
Q

phototransduction and visual pathway

A

Light waves enter the pupil after being refracted from the tear layer and cornea.

  1. The lens further refracts the light onto the retina which is where the photoreceptors are populated (specifically the fovea)
  2. Photons from the light are absorbed by the photopigment (rhodopsin/iodopsin), specifically by opsin. This tunes the light and detects the particular wavelength on the spectrum.
  3. The absorption of light triggers the activation of transducin which activates a phosphodiesterase that hydrolyses cGMP.
  4. In darkness, high levels of cGMP in the outer segment keep sodium channels open, however in the light cGMP levels drop and some of the channels close leading to hyperpolarization of the outer segment. This ultimately reduces the opening of Calcium channels at the synaptic membrane and reduces glutamate being released into the synapse
  5. In the dark, the photoreceptors are in a depolarized state (membrane potential of roughly -40mV). As there is a progressive increase in the intensity of light, it causes the potential across the receptor membrane to become more negative (reaching -65mV)
  6. The drop in the glutamate neurotransmitter signals that light is present
  7. Photoreceptors in the outer plexiform layer stimulate horizontal cells which helps to identify the information that is passing through.
  8. Alongside this, the bipolar cells create direct or indirect connections to the ganglion cells in the inner plexiform layer
  9. The ganglion cells process the electrical information (alongside the amacrine cells). Their axons collectively form the initial part of optic nerve.
  10. The optic nerve (cranial nerve II)  exits via the optic disc on the retina
    a. Anything from the nasal visual field is projected onto the temporal retina
    b. Anything from the temporal visual field is projected onto the nasal retina
    c. (for example, light from the right visual field will hit the left eye’s temporal retina while hitting the right eye’s nasal retina)
  11. After the formation of the optic nerve, it leaves the bony orbit via the optic canal, a passageway through the sphenoid bone. It then enters the cranial cavity running along the surface of the middle cranial fossa.
  12. The optic nerve meets at the chiasm in which;
  13. Axons from the nasal retina cross over to the opposite sides, while the temporal retina information remain on the same side (this means that all information from the left visual field stay together and all information from the right visual field stay together)
  14. The optic tract then synapses with the cells in the lateral geniculate nucleus (part of the thalamus)
  15. Information from the contralateral side goes to layers 1, 4 and 6 of the LGN while information from the ipsilateral side goes to layers 2,3 and 5
  16. It then travels to the primary visual cortex in the occipital lobe via two main pathways;
    a. Upper optic radiation – (baum loop) this pathway carries fibres from the superior retinal quadrants (corresponding to the inferior visual field quadrants)
    b. Lower optic radiation – (Meyers loop) carries fibres from the inferior retinal quadrants (corresponding to the superior visual field quadrants)
  17. In the higher visual centre, it takes either the;
    a. Dorsal pathway (to parietal cortex) which subserves spatial vision providing an image of where the object is
    b. Ventral pathway (to inferotemporal cortex) providing an image of what the object is
24
Q

describe the reltionship between the retinal sides and the visual field

A

the temporal retina receive light from the inner visual fields. their ganglia do not decussate

nasal

25
Q

how do the retinal zones correlate to the visual fields

A

the temporal retinal zones receive light from the inner visual field and their ganglia do not decussate at the optic chaism

the nasal aspects do the opposite

26
Q

nerve fibres from the LGN go where to be processed?

in what layer for they mainly synapse?

where is the primary visual cortex found

A

primary visual cortex

layer 5

in the occipital lobe enar the calcari sulcus

27
Q

the LGN is arranged in a what style of fashion

A

layered modular

28
Q

what are the 2 routes to higher visual centres from the primary visual cortex?

A

dorsal pathway- where- sptial vision- goes to parietal lobe

ventral pathway- what- subserves colour+ object vision- goes to temporal lobe

29
Q

Glaucoma

risk factors

A

causes thinning of the optic nerve fibre layer in the retina and graduallly results in vision loss and ifnleft untreated—– blindness

risk factors:

family history of glaucoma

increasing age

prolonged steroid use

30
Q

age related macula degeneration (ARMD)

A
31
Q

diabetic neuropathy

A

deterioration of the tight blood vessels causing blockage, exudates (plasma leakage), haemorrahges and micro aneurysms

32
Q

retinal vein occlusion

A

blockage of retinal vein

predisposing factors are:

increasing age

systemic hypertension

increased IOP

long sighted eye corrections

33
Q

presbyopia

A
34
Q

cataracts

A

any opcaity of the lens

gradual blurring of vision, seeing double in one eye or increasing sensitivity to glare

risk factors: increasing age, excessive unprotected eye exposure to UV light, smoking, poor nutrition, prolonged steroid use

may be surgically removed by replacing the lens w a clear plastic lens implant

35
Q

Balint syndrome

A
  • neurological visual condition
  • bilateral damage to the parito occipital region (region between the parietal and occipital lobes)
  • spatial perception deficits
  • dorsal stream is only affected

includes:

  • optic ataxia- difficulaty reaching for objects under visual guidance
  • occular apraxia- difficulaty in visual scanning
  • simultanagnosia-
36
Q

damage to the visual system of the brain

A

neurological visual condition

damage to V1- no conscious awareness of being able to see– blindsight impaired

info goes straight to processing

damage to V4- no colour perception or memory of colour, achromatopsia

damage to V5- cannot process motion so objects moving become invisible- akinetopsia

37
Q
  1. visual agnosia
    1. apperceptive visual agnoisa
    1. prosopagnosia
A

cannot perceive visual stimuli correctly

cannot perceive objects

failure to recognise faces- damage to fusiform face area

38
Q

associative visual agnosia

A

inability to identify objects perceived visually

form can be matched w similar objects or drawn from memory

just can’t link photos w words

disruption to connections in the ventral stream o f the visual cortex but no damage to the dorsal stream

39
Q

achromatopsia

A

inability to discriminate among different hues, cannot see colour at all

damage to visual association cortex either bilateral or unilateral

also affects memory of colour

Unit 14 Week 1 (3 decks)

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