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physiology > Lectures 17-20: Sensory Integration > Flashcards

Lectures 17-20: Sensory Integration Flashcards

1
Q

pupil acts as

A

aperture

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2
Q

pigmentation acts as

A

dark chamber

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3
Q

optic nerve acts as

A

communication to central processor

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4
Q

retina:

A
  • sclera
  • choroid
  • Retinal Pigment Epithelium
  • Photoreceptors
  • Horizontal cells
  • Bipolar cells
  • Amacrine cells
  • Retinal Ganglion Cells
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5
Q

Sclera =

A

= white of the eye

  • Protective, outer layer comprised of collagen and elastin fibres
  • Humans possess more sclera than other species with a small iris
    = eye movements can be seen for communication
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6
Q

Choroid =

A
  • Vascular layer providing oxygen and nutrients to outer retina especially fovea
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7
Q

Retinal Pigment Epithelium =

A
  • Pigmented layer for light absorption and reducing oxidative stress
  • Tight junctions forms blood brain (retina) barrier
  • Supports photoreceptors
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8
Q

Photoreceptors =

A

2 types:

  • Cones = concentrated in fovea, high acuity, day (photopic) vision and colour vision (6 million)
    (3 types - blue, red, green)
  • Rods: dark (scotopic) vision. Not present in central retina (100 million)
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9
Q

Horizontal cells =

A

Interneurons connecting photoreceptors laterally

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10
Q

Bipolar cells =

A
  • Connect photoreceptors to retinal ganglion cells

- Facilitate sensory processing through horizontal and amacrine cells

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11
Q

Amacrine cells =

A

Interneurons connecting bipolars laterally

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12
Q

Retinal Ganglion Cells =

A

Output cells from the retina

4 types in humans:

  • Parvocellular
  • Magnocellular
  • Koniocellular
  • Photosensitive ganglion cells
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13
Q

Central retina specialised to allow high spatial vision:

A
  • Long narrow cone outer segments allow high density packing
  • Henle fibres (axons form cone photoreceptors) run obliquely allowing formation of foveal pit (inner layers deflected sideways)
  • Ganglion cells heaped up around the fovea
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14
Q

Visual Acuity:

A

A measure of fine spatial (foveal) vision

Equivalent to 1-2 cone diameter in normal vision

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15
Q

the eyes move to…

A

1) bring an image onto the fovea (saccades)

2) keep it there

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16
Q

types of eye movement…

A
  • Saccades
  • Fixations
  • Smooth Pursuit
  • Optokinetic
    Nystagmus
  • Vestibulo-ocular Reflex
  • vergence movements
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17
Q

saccades eye movements =

A

rapid eye movements to bring an image into fovea

  • short latency
  • voluntary
  • conjugate (both eyes move at same time in same direction)
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18
Q

vestibulo-ocular reflex eye movements =

A

When the head or whole body moves (compensates for head movements)

  • Keeps gaze steady
  • Extremely rapid (immediate)
  • Involuntary, driven by vestibular system (vestibular sensory drive)
  • Conjugate
  • responds best to brief stimulation
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19
Q

smooth pursuit eye movements

=

A

When a single object of interest is moving
(track a single moving target)

  • Requires the brain to estimate how fast the target is moving
  • Voluntary although need to see a moving target to make a pursuit movement
  • Conjugate
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20
Q

optokinetic nystagmus eye movements =

A

When the whole visual field is moving (track movements of visual field)

  • Has a slow phase in direction of target (slow build up) and fast phase to reset eyes
  • Involuntary, but driven by moving visual field
  • Conjugate
  • visual sensory drive
  • responds best to sustained stimulation
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21
Q

fixational eye movements =

A

to keep the fovea on a fixed target of interest

comprised of miniature eye movement:

  • Microsaccades = Small saccades to bring image back towards fovea
  • Drifts = Slower than microsaccades and more random
  • Tremor = Fine oscillations superimposed on the drift
22
Q

vestibular system:

Vestibulo-ocular Reflex

A

ansers where am i goin?and whuch way is up?

Head rotation - (semicircular canals)
= The three semicircular canals lie in 3 orthogonal planes

Head translation -(saccule and utricle)
-=The utricle is sensitive to change in horizontal movement.
=The saccule is sensitive to the change in vertical acceleration (such as going up in an elevator)

23
Q

vergence eye movement =

A
  • Simultaneous movement of both eyes to maintain single binocular vision
  • Image from each eye must be in centre of each retina
  • Allows viewing at different distances

= To view image at near eyes move inwards (convergence)

= To view image at distance eye move outwards (divergence)

  • Voluntary, driven visually
  • Retinal disparity = the way left and right eyes view slightly different images (The greater the disparity between each image, the closer the image to you)
24
Q

pathological nystagamus:

A

= involuntary constant to and fro movement of the eyes that is constant

= Infantile (develops in first few months of life) or acquired in later life due to neurological disease

25
Q

infantile pathological nystagamus can be…

A

no oscillopsia:

  • Idiopathic (no known cause)
  • Albinism
  • Retinal Disease
  • Optic Nerve Disease
26
Q

Acquired pathological nystagamus can be…

A

oscillopsia:

  • Brain disorder
  • Multiple
  • sclerosis
  • Stroke
  • Brain Tumour
  • Ataxia
  • Drug/Alcohol Abuse
27
Q

Recording Eye Movements>

A

Qualitative:
- Video

Quantitative:
2D = 
- Electrooculography
- Limbus tracker
- 2D Videooculography
3D =
- Scleral Search Coil
- 3D Videooculography
28
Q

2D Electrooculography:

A

Corneo-retinal potential – difference in electrical
charge between cornea and retina

Movement of the eye relative to the
electrode produces an electrical
signal that corresponds to the eye position

Easy to use/set-up (children) but output can be noisy

29
Q

2D Limbus Tracker:

A

Measures reflected infrared light shone onto limbus
(border of dark iris and light sclera)

High temporal resolution, non invasive but set-up needs to be precise

30
Q

2D Videooculography

A

Infrared tracking of pupil for eye movement and screen markers for head

High temporal and spatial resolution recordings, but does not record during blinks. Can record gaze (head + eye position)

31
Q

3D Scleral Search Coil

A

Magnetic contact lens inserted into eye

high spatial and temporal
recordings of 3D eye movements, but invasive and uncomfortable

32
Q

3D Videooculography

A

Tracks pupil for & vertical movements and iris to follow torsional

Lower temporal and spatial resolution compared to scleral search coil but non-invasive and comfortable = suitable for clinical setting

33
Q

Idiopathic Infantile Nystagmus:

A
  • Often hereditary
  • Onset in first few months of life
  • No other problems with the visual system
  • Nystagmus amplitude and waveform changes with age
  • Sometimes head nodding
  • Vision usually good (many able to drive)
  • Horizontal
  • Direction and size same in both eyes (conjugate)
  • Null point
  • Abnormal head turn
  • Foveation strategy
34
Q

Albinism:

A
  • Absent or decreased tissue melanin in conjunction with visual system abnormalities (Poor vision)
  • hypopigmentation in iris
  • Chiasmal abnormalities
  • Nystagmus
  • Retinal abnormalities
35
Q

symptoms of Nystagmus:

A
  • Poor vision
  • Sensitivity to light/night blindness
  • Abnormal pupil responses
  • Head nodding
  • Abnormal head turn
36
Q

example of an acquired nystagmus disease:

A

Multiple Sclerosis:

  • demyelination in brain and spinal cord
  • can be relapsing or progressive
  • blurred vision
  • nystagmus
  • oscillopsia
37
Q

possible reasons why there isn’t Oscillopsia in Infantile Nystagmus?

A
  • Plasticity of the brain until about 7 years of age (parietal cortex)
  • Two hypothesis resuppression of oscillopsia in infantile nystagmus:

= Sampling theory: information from the most stable retinal images is used and rest of nystagmus cycle is ignored

= Remapping theory: efference copy signal of nystagmus waveform is used to cancel the effects of motion

38
Q

visual pathway:

A
  1. retina
  2. LGN to V1
  3. V1 to ventral (temporal) pathway
    or V1 to dorsal (parietal) pathway
  4. balance - vision and other senses
39
Q

example 1: Retina

A

Integration of Photoreceptor Inputs into Receptive Fields…

Vertical flow of information:

bipolar cells transfer signals from photoreceptors to retinal ganglion cell outputs (allows 2 regions for signal processing (plexiform layers = dendritic processes))

Vertical flow of information:

  • Horizontal cells – inhibitory cells functioning at the photoreceptor / biopolar cell interface (in the outer plexiform layer)
    → help form receptive fields of RGCs for detecting contrast
  • Amacrine cells – inhibitory cells functioning at the biopolar / retinal ganglion cell interface (in the inner plexiform layer)
    → help form receptive fields of RGCs for detecting motion
40
Q

TYPES OF OUTPUT FROM THE RETINA (Retinal Ganglion Cells)

A

2 main types:

  • PARVOCELLULAR CELLS
    small receptive fields
    detect fine features
    colour sensitive
  • MAGNOCELLULAR CELLS
    large receptive fields, motion sensitive
41
Q

Lateral inhibition greater in…

A

…peripheral retina because larger receptive fields

42
Q

Detection of Contrast…

A

Horizontal cells and the parvocellular output

43
Q

Detection of Motion…

A

Amacrine cells and magnocellular output

44
Q

Starburst Amacrine Cells =

A
  • Central cell body and star shaped dendritic arbour
  • Produces inhibition along dendrites in direction of motion
  • Relative location of retinal ganglion cells to starburst amacrine cells determine their directional selectivity
45
Q

Example 2: Eyes to Brain

A

Integration of Information from Two Sense Organs (the eyes) by the Brain (area V1)

eye > optic nerve > optic chiasm > optic tract > LGN > optic radiation > visual cortex

46
Q

OPTIC CHIASM:

A

Approximately 55% of retinal ganglion cell fibres cross contralaterally at the optic chiasm → fibres from nasal retina cross

IMPLICATIONS:
Each cortical hemisphere sees the opposite visual field
Each cortical hemisphere receives inputs from right and left eyes

47
Q

WHY DO WE NEED AN OPTIC CHIASM?

A

TWO EYES PROVIDING INPUT TO EACH SIDE OF THE BRAIN?

  • Improve signal to noise
  • Better eye-hand co-ordination = improve speed of control
  • Better 3D vision through retinal disparity
48
Q

The amount of crossing at the chiasm is proportional to…

A

the amount of binocular field across species

Lateral eyes – no binocular field but wider coverage

Forward facing eyes – larger binocular field = better binocular vision

49
Q

optic chiasm provides retinal disparity through the separation of the two eyes for 3D vision…

A

RETINAL DISPARITY

Horoptor = surface where no disparity between two eyes (images correspond)
Everything nearer = crossed disparity
Everything further away = uncrossed disparity

50
Q

Neural Basis of Retinal Disparity Primary visual cortex (or Area V1):

A

The main cortical receiving station of visual information…

Area V1 is retinotopic:

  • The retina is mapped spatially onto primary visual cortex
  • Cortical magnification of fovea region (another reason we move our eyes)
  • OCULAR DOMINANCE COLUMNS - alternating stripes across the visual cortex from left and right eyes
  • Equivalent representations of visual fields from each eye brought together in area V1
51
Q

strabismus:

A

In strabismus the input from one eye is supressed to prevent double vision

Also causes reduced stereopsis (i.e. depth perception based on using two eyes)

Can be tested in the clinic (e.g. Frisby stereotest)

52
Q

amblyopia:

A

= rduced vision in one eye

Amblyopia can be reversed by patching better eye during visual development (i.e. less than 7 years of age)
- example of neural plasticity in response to visual experience

physiology (8 decks)

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