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eLCRS - 뉴로 > Neuro 12: Neurology Of The Visual System > Flashcards

Neuro 12: Neurology Of The Visual System Flashcards

1
Q

Define the visual pathway

A

Visual pathway = neurological pathway where by vision is converted to neurological impulses —> to be transmitted from the eye to the visual cortex to the posterior part of the brain

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2
Q

The eye is connected to the brain via the ———— nerve

A

Optic nerve (aka cranial nerve)

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3
Q

What is the optic nerve made out of ?

A

Made up of myelinated ganglion nerve fibres

With cell bodies originating in the retina

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4
Q

Optic nerves from both eyes converge at the

A

Optic chiasma

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5
Q

Half of gamglionic nerve fibres Cross at:

While the remaining ganglion nerve fibres:

A

1/2 - Cross at the optic chiasma then goes along the contralateral optic tract
1/2 - exit along the optic tract on the same side

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6
Q

What does the primary visual cortex do?

A
  • Primary Visual Cortex,

relays visual information to the Extra-striate Cortex,
a region adjacent to the Primary Visual Cortex,

–> for further higher visual processing.

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7
Q

Ganglion nerve fibres originate within:

A

the retina –>synapse upon the next order neurons,

at the Lateral Geniculate Nucleus.

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8
Q

What is the lateral geniculate nucleus?

A

a relay centre situated within the Thalamus.

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9
Q

Optic Radiation relaying signal from :

to:

A

from the Lateral Geniculate Ganglion,

to the Primary Visual Cortex within the occipital lobe,
–> lower visual processing.

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10
Q

the primary visual cortex (striate cortex) relays visual info to:

A

the extra striate cortex for further higher visual processing

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11
Q

List the visual pathway

A

eye –> optic nerve –> optic chasm or optic tract –> nerve fibres synapse at lateral geniculate nucleus –> optic radiation –> striate cortex –> extra striate cortex

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12
Q

What are first order neurons?

A
  • rod + cone retinal photoreceptors
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13
Q

What are seconds order neurons?

A
  • retinal bipolar cells
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14
Q

What are third order neurons ?

A
  • retinal ganglion cell
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15
Q

Retinal ganglion fibres terminate at the _____ _____ ______ and synapse upon the ___th order neurons

A

Retinal ganglion fibres terminate at the LATERAL GENICULATE GANGLION and synapse upon the
4th order neurons

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16
Q

Lesions ______ to optic chiasma affects the visual field in one eye only

A

anterior

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17
Q

Lesions ______ to optic chiasma affects the visual field in both eyes

A

posterior

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18
Q

Crossed fibres originate from the _____ ______

A

nasal retina

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19
Q

What are crossed fibres responsible for?

A
  • responsible for temporal visual field
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20
Q

What are uncrossed fibres responsible for?

A
  • responsible for nasal visual field
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21
Q

uncrossed fibres originate from the _____ ______

A

temporal retina

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22
Q

What happens upon a lesion at the optic chiasma?

A
  • it damages crossed ganglion fibres from nasal retina in both eyes
  • results in temporal field deficit in both eyes

–> bitemporal hemianopia

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23
Q

What happens upon a lesion posterior to optic chiasma?

A

RHS lesion –> (left homonymous) –> hemianopia in both eyes

LHS lesion –> (right homonymous) –> hemianopia in both eyes

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24
Q

What is bitemporal hemianopia usually caused by?

A
  • enlargement of pituitary gland tumor
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25
Q

WHat is homonymous hemianopia typically caused by?

A
  • typically caused by stroke
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26
Q

Where is the primary visual cortex located at ?

A
  • located along calcimine sulcus in the occipital lobe
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27
Q

What does the primary visual cortex specials in ?

A
  • specialises in processing visual information of static + moving objects
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28
Q

Right hemispherefield from both eyes projects to ____ primary visual cortex

Left hemifield from both eyes projects to the _____ primary visual cortex

A

Right hemispherefield from both eyes projects to LEFT primary visual cortex

Left hemifield from both eyes projects to the RIGHT primary visual cortex

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29
Q

How is the primary visual cortex organized?

A
  • organised as column with unique sensitivity to visual stimulus of a particular orientation
  • right eye + left eye dominant columns are arranged alternatively
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30
Q

Damage to the primary visual cortex due to stroke may result in>

A

homonymous hemianopia of the contralateral side

with characteristic sparing of the macula central vision.

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31
Q

What is the function of extra striate cortex?

A

it converts basic visual information such as position + orientation into complex human precepts like motion + object representation

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32
Q

What is the pupillary function?

A

it regulates light input into the eye

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33
Q

What happens to pupil in light?

A

pupil constriction

- iris circular muscle contracts

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34
Q

What happens to the pupil in dark?

A

pupil dilation

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35
Q

why does the pupil constrict in light?

what is this action mediated by?

A
  • reduces amount of light entering the eye
  • and so reduces rate of photo-pigment bleaching

mediated by: Parasympathetic nerve

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36
Q

why does the pupil dilate in dark?

what is this action mediated by?

A
  • increases amount of light entering the eye
  • increases light sensitivity

mediated by: sympathetic nerve

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37
Q

PUPILLARY REFELX : describe the afferent pathway

A

????????????????

38
Q

PUPILLARY REFELX : describe the efferent pathway

A
  • provided by parasympathetic nerve which synapses at the ciliary ganglion
    ????????????
39
Q

What is the difference between direct and consensual reflex?

A

Direct: constriction of pupil of light stimulated eye

Consensual: constriction of pupil of the other eye

–> because afferent pathway on either side alone –> will stimulate efferent pathway on both sides.

40
Q

What would happen in right afferent defect?

A
  • e.g damage to right optic nerve

RIght eye stimulation:
- no pupillary constriction in both eyes when right eye

BUT
Left eye stimulation: normal pupillary response in both eyes

41
Q

What would happen in right afferent defect?

A

e.g damage to right 3rd neve

Right eye stimulation:

  • no pupillary constriction in right eye
  • normal pupillary constriction in left eye

left eye stimulation:

  • no pupillary constriction in right eye
  • normal pupillary constriction in left eye
42
Q

What is the difference between unilateral AFFERENT and EFFERENT defect ?

A

UNILATERAL AFFERENT DEFECT: response is different depending on which eye is stimulated

UNILATERAL EFFERENT DEFECT: unequal response is same no matter if left or right eye is stimulated.

43
Q

How is the swinging torch test conducted?

A
  • stimulate one eye at a time , alternating between right + left eye
44
Q

If there is a relative afferent pupillary defect, what would you see in a swinging torch test?

A

Both pupils constrict,
when light swings to the left eye with intact afferent pathway.

Both pupils will paradoxically dilate,
when the light swings to the right eye with damaged afferent pathway,
as a result of relatively reduced drive for pupillary constriction in both eyes.

45
Q

What is the definition of Eye movement ?

A
  • voluntary or involuntary movement of the eyes, necessary for tracking visual stimuli
46
Q

Eye movement = facilitated by _ extra ocular muscles

–> innervated by _ cranial nerves

A

Eye movement = facilitated by 6 extra ocular muscles

–> innervated by 3 cranial nerves

47
Q

What is duction?

A

eye movement in one eye

48
Q

What is version?

A

simultaneous movement of both eyes in same direction

49
Q

What is vergence?

A

simultaneous movement of both eyes in opposite direction

50
Q

What is convergence?

A

simultaneous inward movement in both eyes –> when viewing a near object

51
Q

What is Saccade

A
  • short, fast burst eye movement

- both voluntary + involuntary

52
Q

What is the purpose of Saccade?

A
  • useful for acquiring new external target
  • for scanning text
  • for tracking objects
  • or for performing eye movement guided by memory\
  • up to 900 deg/sesc
53
Q

What is smooth pursuit?

A
  • it is a slow sustain movement
  • involuntary
  • up to 60 deg /s
54
Q

How many extraocular muscles are there?

A

6

55
Q

What does the extra ocular muscle do?

A
  • attaches eyeball to orbit

- provides straight + rotary movement

56
Q

What are the 4 straight muscle?

A
  1. superior rectus
  2. inferior rectus
  3. lateral rectus
  4. medial rectus
57
Q

What does the superior rectus do?

A
  • attached to eye at 12 o’clock

- moves the eye up

58
Q

what does the inferior rectus do?

A
  • attached to eye at 6 oclock

- moves the eye down

59
Q

What does the lateral rectus do?

aka external rectus

A
  • attaches on temporal side of the eye

- and moves the eye towards to outside of the head –> towards the temple

60
Q

What does the medial rectus do?

aka internal rectus

A
  • attaches on nasal side of the eye

- moves eye towards the middle of the head –> towards nose

61
Q

where is the superior oblique muscle located at?

A
  • it is attached high on temporal side of the eye

- passes under the superior rectus

62
Q

What does the superior oblique muscle do?

A
  • it moves the eye in a diagonal pattern

down + in

63
Q

where is the inferior oblique muscle located at?

A
  • it is attache slow on the nasal side of the eye

- and passes over the inferior rectus

64
Q

What does the inferior oblique muscle do?

A
  • it moves the eye in a diagonal pattern

up and out

65
Q

The lateral rectus muscle = innervated by:

A

The lateral rectus muscle = innervated by: 6th cranial nerve ABDUCENS NERVE

66
Q

The superior oblique muscle = innervated by:

A

The superior oblique muscle = innervated by: 4th cranial nerve TROCHLEAR NERVE

67
Q

apart from lateral rectus muscle + superior oblique muscle, all other extra ocular muscles = innervated by:

A

apart from lateral rectus muscle + superior oblique muscle, all other extra ocular muscles = innervated by: 3rd cranial nerve OCULOMOTOR NERVE

–> superior oculomotor nerve = superior rectus muscle

–> inferior oculomotornerve = rest

68
Q

How is lateral rectus muscle action best tested?

A

in abducted position

69
Q

How is medial rectus muscle action best tested?

A

in adducted position

70
Q

How is superior rectus muscle action best tested?

A

in elevated + abducted position

71
Q

How is inferior rectus muscle action best tested?

A

in depressed + abducted position

72
Q

How is inferior oblique muscle action best tested?

A

in elevated and abducted position

73
Q

How is superior oblique muscle action best tested?

A

in depressed + abducted position

74
Q

elevation of one eye =

elevation of both eyes =

A

elevation of one eye = supraduction

elevation of both eyes = supraversion

75
Q

depression of one eye =

depression of both eyes =

A

depression of one eye = infraduction

depression of both eyes = infraversion

76
Q

dextroversion (right gaze) =

A
  • simultaneous right eye abduction
    AND
  • left eye adduction
77
Q

Levoersion (left gaze) =

A
  • simultaneous left eye abduction
    AND
  • right eye adduction
78
Q

what is adduction

A
  • duction movement of one eye

- -> moving towards nose

79
Q

What is abduction?

A
  • duction movement of one eye

- -> moving AWAY from nose

80
Q

What happens 3rd nerve palsy?

A

lateral rectus muscle + superior oblique muscle = not working

  • eye adopts down and out position
  • droopy eyelid
81
Q

What happens in 6th nerve palsy?

A
  • affected eye = unable to abduct
  • -> and deviates inwards
  • when patient is asked to abduct affected eye, affected eye deviates INWARDS
82
Q

Optokinetic Nystagmus reflex

A

is an oculomotor reflex closely linked to the vestibular system which contributes to the stabilisation of retinal images.

It is seen when an individual follows a moving object with their eyes, which then moves out of the field of vision at which point their eye moves back to the position it was in when it first saw the object.

83
Q

what is meant by convergence?

A

convergence = no. of lower order neurons field synapsing on raw same high order neurone

84
Q

cone system convergence > rod system convergence

A

-

85
Q

differentiate between high and low convergence

A

low :

  • small receptive field
  • fine visual activity
  • low light sensitivity

high :

  • large receptive field
  • coarse visual activity
  • high light sensitivity
86
Q

differentiate between on centre ganglion + off centre ganglion

A

on centre ganglion

  • stimulated by light at centre of receptive field
  • inhibited by light on the edge of the receptive field

off centre ganglion

  • inhibited by light at centre of receptive field
  • stimulated by light on edge of receptive field

note:
important for = contrast sensitivity + enhanced edge detection

87
Q

What are the 2 types of retinal ganglion cells?

A
  • off centre ganglion

- on centre ganglion

88
Q

humans have 2 eyes anteriorly –> which allows 3D vision (depth) of a particular object

A

-

89
Q

What does the extra striate cortex do ?

A
  • area around primary visual cortex within the occipital lobe
  • which coverts basic visual info orientation and position into complex info.
90
Q

what is meant by torsion?

A

rotation of eye around anterior = posterior axis of the eye

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