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Unit 14 Week 1 (Tommy) > 14.1 The Neurobiology of Vision > Flashcards

14.1 The Neurobiology of Vision Flashcards

1
Q

Label the diagram

A
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2
Q

Label the diagram and the lobes

A
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3
Q

Where do the nerves from the retina go?

A
  1. The nerves leave the eye in the optic nerve and synapse in the lateral geniculate nucleus (LGN)
  2. Fibres then go to the visual cortex

Transmits all light information into electical information to the brain

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4
Q

Label the diagram

A
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5
Q

What is the purpose of the cornea?

A
  • Involved in focusing light into eye
  • Transparent covering over eye: is a barrier between outside world and inner eye
  • Refracts light entering the eye
  • NO blood vessels
  • VERY sensitive to light
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6
Q

What is the purpose of the pupil?

A
  • Small opening in eye by which light passes
  • Size of pupil can change which can be due to light or emotion (e.g. like someone pupil dilates)
  • LOW light –> pupils dilate, more light into eye
    • better to see when dark
  • HIGH light –>pupils constrict
    • ​LESS light into eye
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7
Q

What is the iris?

A
  • The coloured portion of the eye
  • Regulates the amount of light into the eye
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8
Q

What is the purpose of the lens?

A
  • Serves by focusing light to back of eye (refracts)
  • Transparent structure that helps refract light onto retina
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9
Q

What is the fovea?

A
  • Indentation (small) at the back of the eye where there is high level detail processing of light
  • Region where upper retinal layers are THINNED
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10
Q

What flips the inverted image from the retina?

A

The vision cortex

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11
Q

What is vision?

A

Transduction of light

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12
Q

What produces tears?

A

Lacrimal gland produces tears and passes through the lacrimal ducts

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13
Q

What does vision depend on?

A

Depends on light sensitive cells in the retina at the rear of the eye

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14
Q

How does light reach the retina?

A

Light is focussed by the cornea and lens onto the retina

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15
Q

Explain the structure of the retina (layers)

& label the diagram

A
  • Photoreceptors (allow night vision)
    • ​Made of cones and rods
    • CONES
      • ​More in centre of retina
      • Only type in fovea of eye
    • RODS
      • More in outer areas of the eye
      • Used for peripheral vision
  • Outer plexiform layer
  • Horizontal layer
    • ​Form synapses with bipolar cells & photoreceptor cells
  • Bipolar cell
    • ​Connect photoreceptors to ganglion cells
  • Amacrine cell
    • ​Translate information
  • Inner plexiform layer
  • Ganglion cell
    • Gets info from retina & sends onto brain (via optic nerve)
    • Their axons leave the eye
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16
Q

What do photoreceptors do & how?

A
  • Photoreceptors capture light
  • Have outer segments with stacks of membrane that increases their surface area greatly
  • Pigment molecules collect light
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17
Q

What is a photon?

A

A single unit of light

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18
Q

What is the wavelength of visual light and colours on the sides of the spectrum?

A

(BLUE) 380-750nm (RED)

Infra red Ultra-violet

19
Q

What are the kinds of photoreceptors?

A
  • 120 million RODS (more rods in nocturnal animals)
  • 6 million CONES
  • RODS
    • ​More sensitive to light and occur in the periphery (at low light)
  • CONES
    • Respond to different wavelengths
    • Mainly found in the fovea (day-light, when HIGH levels of light)
20
Q

What are these and label them and what is the difference between the two?

A

The outer segments are different

21
Q

Label this fundoscopy image

A
22
Q

Label this diagram & briefly explain it

A
  • At the fovea (where information from the lens is focussed) there is a 1:1 ratio of photoreceptors : ganglion cells
  • At the retina there is a 50:1 ratio of photoreceptors : ganglion cells
23
Q

Explain receptor potentials in photoreceptors, bipolar cells, ganglion cells

A
  • Photoreceptors
    • ​HYPERPOLARISING membrane potential following stimulus
  • Bipolar cells
    • DEPOLARISING membrane potential
  • Ganglion cells
    • Recording of action potentials then sends it to the brain
24
Q

How many types of rods & cones are there?

A
  • Cones
    • ​Blue
    • Green
    • Red
  • Rods
    • Blue/green
25
Q

Explain the anatomy of the visual system after the ganglion cell fibres

A
  1. Ganglion cell fibres enter the optic nerve & then the optic chiasm
  2. Fibres from the nasal retina cross over (CONTRALATERAL - opposite side)
  3. Fibres from the temporal retina remain (IPSILATERAL - same side)

LGN - Lateral geniculate nucleus

  1. Nerve fibres from LGN go to the visual cortex
  2. Synapse mainly in layer IV of cortex (primary visual cortex - at posterior of brain in occipital lobe)
26
Q

What are the pathways from the primary visual cortex?

A
  • Dorsal pathway –> spatial vision e.g. WHERE something is (FAST)
    • To parietal cortex
  • Ventral pathway –> colour and object vision e.g. WHAT (detail of what looking at) (SLOW)
    • To inferatemporal cortex
27
Q

Explain disorders of vision

A
  • Is rare in females
  • More common in males as on X chromosome (1 in 10)
  • Visual disorders can occur anywhere in the visual pathway
  • Short & long sightedness
  • Neural deficits
    • Colour blindness - caused by loss of one type of cone
    • Optic (retinal) neuropathy - specific to the retina, blood vessel damage & regrowth
28
Q

What is glaucoma & the risk factors?

A
  • When there is damage in the connection between the eye & the brain (usually in the optic nerve)
  • Up to 50% of people with disease don’t know they have it
  • Causes thinning of the nerve fibre layer in the retina and gradually results in loss of vision and untreated glaucoma eventually leads to blindness
  • Risk factors:
    • Family history of glaucoma
    • Increasing age
    • Prolonged steroid use
29
Q

What is AMD & the risk factors?

A
  • AMD - age related macular degeneration
  • Commonest cause of blindness in western world
  • Peripheral vision remains unaltered (causes blurry vision, wavy/distorted lines or a central blind spot
  • Risk factors:
    • Increase age
    • Female
    • Smoking
30
Q

Explain diabetic retinopathy

A

Deterioration of the tight junctions of blood vessel wall causing blockage, excudates (plasma leakage), haemorrhages, micro aneurysms

31
Q

Explain retinal vein occlusion & predisposing factors

A
  • Blockage of a retinal vein. Predisposing factors are:
    • Increasing age
    • Systemic hypertension
    • Raised Intra ocular pressure and long sighted spectacle corrections
  • There is some visual loss depending on the severity of the occlusion but some recovery after 6 months
32
Q

Explain presbyopia

A
  • Means ‘old eye’ (can be particularly due to eye muscles)
  • Ages of 40-45 showing difficulties with reading. Other symptoms include holding reading material further from the eyes and blurry distance vision immediately after reading
  • Due to the lens becoming inelastic making focusing on near objects difficult. Rectified by the use of bifocals, varifocals, separate reading spectacles or contact lenses
33
Q

Explain cataracts & how it can be treated

A
  • Any opacity of the lens. May present as gradual blurring* of the vision, seeing *double in one eye or increased sensitivity to glare
  • Cataracts are more common with increasing age. Excessive unprotected exposure to UV light, smoking, poor nutrition and prolonged steroid use also contribute
  • Cataracts can be removed surgically by replacing the lens* with a clear *plastic lens implant
34
Q

Explain Balint’s syndrome

A
  • Bilateral damage to parieto-occipital region
    • Region between parietal and occipital regions
    • Involved in spatial perception
    • Dorsal stream only is affected
  • Includes:
    • Optic ataxia
      • Difficulty reaching for objects under visual guidance
    • Ocular apraxia
      • Difficulty in visual scanning
    • Simultanagnosia
      • Difficulty perceiving more than one object at a time
35
Q

What is optic ataxia?

A

Difficulty reaching for objects under visual guidance

36
Q

What is ocular apraxia?

A

Difficulty in visual scanning

37
Q

What is simultanagnosia?

A

Difficulty perceiving more than one object at a time

38
Q

Explain what happens when there is damage to V1

A
  • No conscious awareness of being able to see
    • Known as Blindsight
  • ​Information goes straight for processing so information retained but without awareness
  • Patients report a ‘gut feeling’ but insist they cannot see
39
Q

Explain what happens when there is damage to V4

A
  • No colour perception OR memory of colour
    • Achromatopsia
40
Q

Explain what happens when there is damage to V5

A
  • Cannot process motion so objects moving become invisible
    • Akinetopsia
41
Q

Explain what happens when there is widespread damage to all but V4

A
  • Severely impaired visual processing but colour information retained
    • Chromatopsia
  • Caused by carbon monoxide poisoning
42
Q

What is visual agnosia & types?

A

Cannot perceive visual stimuli accurately

  • Apperceptive visual agnosia
    • Cannot perceive objects
  • Prosopagnosia
    • Failure to recognise faces
    • Damage to fusiform face area
      • Region of extrastriate cortex dedicated to face and complex object recognition
  • Associative visual agnosia
    • Inability to identify objects perceived visually
      • Form can be matched with similar objects or drawn from memory
      • Can still describe what objects are when named
        • Just can’t link pictures and words
    • Disruption to connections in ventral stream of the visual cortex
      • But no damage to those in the dorsal stream
43
Q

What is achromatopsia & explain it

A
  • Inability to discriminate among different hues (a colour/shade)
  • Cannot see colour at all
  • Damage to visual association cortex
    • Bilateral
      • Affects both visual fields
      • NO memory of colour
    • Unilateral
      • Only affects one visual field
      • Half the world is seen in grey-scale
      • Half the world is seen in colour
  • Also affects memory of colour
    • Patients cannot recall what colours objects were prior to brain injury

Unit 14 Week 1 (Tommy) (3 decks)

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