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LCRS Neuro > Visual pathway > Flashcards

Visual pathway Flashcards

1
Q

pathway from eyes to primary visual cortex

A
  • the eye
  • optic nerve (ganglion nerve f)
  • optic chiasm (where half of the fibres decussate)
  • optic tract (where ganglion fibres synapse in the lateral geniculate nucleus)
  • optic radiation (4th order)
  • PVC/striate cortex
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2
Q

light pathway to receptive ganglion cell

A
  • first order: rod and cone photoreceptor
  • second order: retinal bipolar
  • third order: retinal ganglionic
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3
Q

what proportion of fibres decussate at the optic chiasm?

A

53% of the retinal ganglionic fibres decussate at the optic chaise then synapse at the lateral geniculate nucleus (LGN) in the thalamus

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4
Q

what is the LGN, where is it located?

A

lateral geniculate nucleus

in the thalamus

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5
Q

size of receptive field with distance from fovea

A

receptive field size increases with distance from the fovea

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6
Q

what is convergence?

compare between cones and rods

A

rods use high convergence while cones use low convergence

  • convergence: number of lower order neurones synapsing at the same high order neurone
  • cones tend to be 1:1 i.e. lower order of convergence while in the rods, there are usually many to one e.g. 1:4:8
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7
Q

central and peripheral retinal convergence comparison

A

central has lower convergence

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8
Q

what is the result on the receptive field
visual acuity
and light sensitivity
as a result of LOW convergence?

A

small receptive field
fine visual acuity
low light sensitivity

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9
Q

what is the result on the receptive field
visual acuity
and light sensitivity
as a result of HIGH convergence?

A

large receptive field
course visual acuity
high light sensitivity

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10
Q

what are the two groups of retinal ganglionic cells?

what are they important for?

A

on centre and off centre ganglionic cells

important for:
contrast sensitivity
edge detection

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11
Q

difference between on centre and off centre ganglionic cells

A

on centre: stimulated by light at the CENTRE of the receptive field, therefore inhibited by light on the edge of the field

off centre: stimulated by light on the EDGE of the receptive field, therefore inhibited by light in the centre of the field.

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12
Q

what lesion affects one eye only?

A

anterior (to optic chiasm) lesions

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13
Q

what lesion affects both eyes?

A

posterior (to optic chiasm) lesions

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14
Q

which part of the retina produce crossed fibres at the optic chiasm?

what is it responsible for?

A

nasal retina

temporal visual field (light from the sides)

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15
Q

what sort of fibre originates from the temporal retina?

what is the temporal retina used for?

A

uncrossed fibres

nasal visual field

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16
Q

what is the result of lesion at the optic chiasm? why?

A

bitemporal hemianopia

  • both eyes’ nasal retinas are affected as they are the crossing retgang fibres
  • nasal retina receives temporal visual field
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17
Q

what is the result of damaging the crossing RGC fibres in a optic chiasm lesion?

A

bitemporal hemianopia

as both sets of nasal retina fibres (responsible for temporal visual field) are damaged in the lesion

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18
Q

what is the result of a lesion posterior to the optic chiasm?

A

right lesion—> left homonymous hemianopia

left lesion–> right homonymous hemianopia

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19
Q

what is another cause of bitemporal hemianopia, in addition to an Optic Chiasm lesion?

A

enlargement of a pituitary gland tumour causing its compression

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20
Q

what can cause homonymous hemianopia?

A

stroke

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21
Q

in which disorder is central acuity retained? what is actually affected?

A

macular sparing disorder

peripheral vision is lost

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22
Q

what condition causes a loss of horizontal plane vision?

A

glaucoma

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23
Q

what plane do neurological problems often affect?

A

vertical plane of vision

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24
Q

along which fissure is the PVC located?

A

along the calcarine fissure

Characterised by a distinct stripe derived from the myelinated fibre of the optic radiation projection.

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25
Q

why is the macula disproportionately presented as a large area?

A

due to a higher density of RGCs (lower convergence)

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26
Q

where relative to the calcarine fissure is the superior visual field?

A

projection is below the fissure

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27
Q

what is located above the calcarine fissure?

A

inferior visual field

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28
Q

in which direction do the left and right semi-field project

A

right and left (opposite) respectively

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29
Q

how is the PVC organised in the brain in terms of light sensitivity?

A

In columns with unique sensitivity to the visual stimulus of a particular orientation

alternation of right and left eye columns

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30
Q

what is the common cause of macular sparing homonymous hemianopia?

A

damage to PVC often due to stroke (of the PCA)

macula sparing due to dual blood supply by PCAs

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31
Q

why is the macula spared in contralateral homonymous hemianopia (with macula sparing)?

A

due to the dual supply received by the macula

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32
Q

what is the area that surrounds the visual cortex?

A

extrastriate cortex

  • assists the striate cortex with position and orientation ,makes use of the dorsal and ventral pathways
  • the striate cortex is part of the visual cortex that processes visual information from the lateral geniculate nucleus (thalamus)
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33
Q

what is the function of the extrastriate complex?

A

convert basic visual info, orientation and position into complex info

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34
Q

where does the dorsal pathway go from the PVC?

A

into the posterior parietal cortex via extrastriate cortex

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35
Q

what is the dorsal pathway from the PVC responsible for?

A

motion detection

visually-guided action

36
Q

what is the result of damaging the dorsal pathway from the PVC?

A

motion blindness

37
Q

where does the ventral pathway from the PVC go?

A

to the inferiotemporal cortex via the extrastriate cortex

38
Q

what is the ventral pathway from the PVC responsible for?

A

object representation
facial recognition
detailed fine central vision
colour vision

39
Q

what is the result of damage to the ventral pathway from the PVC?

A
  • prosopagnosia (facial agnosia)

- cerebral achromatopsia (partial or total absence of color vision)

40
Q

what is the function the pupillary function in light?

A
  • decreases spherical aberrations and glare,
  • increases depth of field
  • reduces bleaching of photopigments
41
Q

what innervation and nerve mediated constriction in the reflex?

A

CN III (PNS nerve branch)

42
Q

what is the function of the pupillary reflex in the dark?

A

let in more light

43
Q

what innervation mediates dilation?

A

SNS nerve

44
Q

Outline the afferent pathway of the pupillary reflex from the photoreceptor

A
  • light hits photoreceptors
  • bipolar cell
  • ganglionic cell
  • optic nerve
  • optic chiasm
  • optic tract (exit at posterior third and enter LGN)
  • synapse at Pretectal Area
  • synapse at EW nucleus (both ipsilateral and contralateral)
45
Q

which nucleus does the afferent pathway of the pupillary reflex first synapse to, in the brainstem?

A

pretecal nucleus

then the Edinger-Westphal

both are located in the midbrain

46
Q

efferent pathway of the pupillary reflex from the Edinger Westphal nucleus?

A
  • EW nucleus
  • CN III nerve efferent
  • synapse at ciliary ganglion
  • via short posterior ciliary nerve (from ganglion)
  • pupillary sphincter
47
Q

what does a stimulus in the afferent pathway have on the efferent?

A

light from one eye stimulates the efferent pathway in both eyes

48
Q

direct vs consensual light reflex

A

direct: constriction in the pupil of light stimulated eye
consensual: constriction of the other eye

49
Q

what is the effect of a right afferent of the pupillary light reflex (i.e. damage to CN II)

A

no pupil reflex in both eyes

50
Q

what is the effect of a defect on one side, e.g. right, efferent (i.e. damage to CN III) ?

A

no right pupil constriction at all

left one constricts when either eye is stimulated

51
Q

what can be done to demonstrate the weakness of afferent pathway?

result on constriction in normal and defected pathway?

A

swinging torch test, determine incomplete or relative damage to afferent pathway

intact pathway will have both eye constrict with light stimulation
in afferent pathway weakness, both eye paradoxically dilate due to reduced drive to constrict both eyes

52
Q

how many extra ocular muscles are there?

how many cranial nerves innervate them?

A

6 muscles (4 straight, 2 oblique)

innervated by 3 cranial nerves

53
Q

4 types of movement of the eye

A

1) duction (one eye)
2) version (eyes in the same direction)
3) vergence (outward)
4) converge (inward)

54
Q

what does duction mean?

A

movement in one eye

55
Q

version definition (eye movement)

A

movement of both eyes in the same direction

56
Q

left and right version of eyes prefix

A

right = dextroversion

left =levoversion

57
Q

vergence definition (eye movement)

A

movement of both eyes in opposite directions

58
Q

convergence definition (eye movement)

A

simultaneous adduction (inwards towards midline) movement in both eyes when viewing a near object

59
Q

fast speed eye movement

examples of types

A

saccade

e. g. reflexive saccade
e. g. scanning saccade
e. g. predictive saccade
e. g. memory-guided saccade

60
Q

slow speed eye movement

A

smooth pursuit

61
Q

rate in saccade

A

900 deg per second

short, fast burst of movement

62
Q

rate in smooth pursuit

A

60 deg per second

63
Q

what drives smooth pursuit eye movement

A

motion of moving target across the retina

64
Q

what are the 4 straight muscles of the eye?

A

superior rectus= up movement

inferior rectus= down movement

medial rectus
lateral rectus

65
Q

which straight muscle(s) are innervated by CN III

A

superior, inferior and medial rectus

66
Q

which straight muscle(s) are innervated by CN VI

A

lAteral rectus (abducens)

67
Q

what are the 2 oblique muscles?

A

superior oblique

inferior oblique

68
Q

attachment of superior oblique muscle

movement of eye?

A

high on temporal side of eye
passes under superior rectus

moves eye down and out

clinical test: in and down

69
Q

attachment of inferior oblique muscle

movement of eye?

A

low on nasal side of eye
passes over inferior rectus

moves eye up and out

clinical test: move in and up

70
Q

innervation of superior oblique

A

CN IV (trochlear)

71
Q

innervation of inferior oblique

A

CN III (oculomotor)

72
Q

3 nerves that innervate the eye muscles

which muscles do they innervate?

A

CN III- inferior oblique, superior rectus, inferior rectus, medial rectus
CN IV- superior oblique
CN VI- lateral rectus

73
Q

testing movement of lateral rectus

A

abduction (away from midline)

74
Q

testing movement of medial rectus

A

adduction (towards the midline)

75
Q

testing movement of superior rectus

A

abduct then elevate (out and up)

76
Q

testing movement of inferior rectus

A

abduction and depression (out and down)

77
Q

testing movement of inferior oblique

A

move eye medially and elevate (in and up)

78
Q

testing movement of superior oblique

A

depression and adduction

79
Q

presentation of 3rd nerve palsy

A
  • eye droops and abducts (down and out)
  • eyelid droop
  • lateral rectus and superior oblique take over
    unopposed lateral rectus (at the medial rectus is gone) takes over by abducting and the superior oblique also takes over (as inferior oblique is gone)
80
Q

presentation of 6th nerve palsy

A

Diplopia:

  • affected eye unable to abduct and deviates to midline (adduct)
  • therefore double vision- worsens on gazing to side of affected eye
81
Q

what speeds of eye movement are present in optokinetic nystagmus reflex?

A

smooth pursuit and fast paced reset saccade

82
Q

how is visual acuity tested in pre-verbal children

A

presence of nystagmus movement observed (test for reflex)

if reflex is present, the child has the visual acuity to perceive motion

83
Q

what is the effect of cold and warm water in the caloric reflex test?

A

COWS

cold–> opposite
- cold water imitates stimulation of the opposite ear (head is turning the opposite direction) so the eyes in response look to the ipsilateral ear (ear receiving water) whilst nystagmus occurs to the opposite ear

warm–> same
- warm water imitates stimulation of the same ear (head is turning the same direction as ear getting water) so the eyes look to the contralateral ear whilst nystagmus is towards the same ear (ear receiving water)

84
Q

what effect does warm water have on nystagmus?

A

nystagmus to ipsilateral ear

  • warm water causes endolymph in the horizontal canal to rise
  • mimic a head tilt to the ipsilateral side
  • causing an increasing firing of the afferent nerve
  • the eyes will therefore move to the contralateral eye
  • horizontal nystagmus to the ipsilateral ear
85
Q

what effect does cold water have on nystagmus?

A

nystagmus to contralateral side

  • endolymph falls
  • decreased afferent firing
  • mimic head turn to the contralateral side
  • eye moves to ipsilateral side
  • nystagmus to contralateral ear

COWS
applies to the direction of head turn and the resulting NYSTAGMUS (not the normal reflex movement of eyes)

86
Q

what is RAPD?

A

Relative Afferent Pupillary Defect

  • afferent damage leads to weakening of the pupillary reflex (not complete loss)
  • BOTH eyes show a weakened constriction response
87
Q

what is seen with the swinging torch test in RAPD?

A
  • when going from the healthy eye to the affected eye, there will be paradoxical dilation
  • it initially constricted when the other healthy eye had stimulation
  • now the light is in the defected afferent eye, the pupil doesn’t respond (as if there were no stimulus) and it dilates back to normal position despite the light being there

LCRS Neuro (19 decks)

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