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Year 2 - Neuroscience > The Neurology of The Visual System > Flashcards

The Neurology of The Visual System Flashcards

1
Q

Total Visual Path?

A
  1. Eye
  2. Optic nerve - ganglion nerve fibres
  3. Optic chiasm - HALF of fibres decussate here
  4. Optic tract - ganglion fibres exit as optic tract
  5. Lateral Geniculate Nucleus (LGN) - ganglion fibres synapse in nucleus
  6. Optic radiation - 4th order neuron
  7. Primary visual cortex OR striate cortes (occipital love)

ONENOTE!!

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2
Q

Visual pathway of the Retina? (light pathway)

A
  1. 1st order neuron - photoreceptors
    o rods and cones retinal
  2. 2nd order neuron - bipolar cells
  3. 3rd order neuron - ganglionic cells
    o travel down length of optic nerve
    o have PARTIAL decussation at optic chaism
    o Fibres synapse at LGN located within the thalamus
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3
Q

Define Receptive Field

A

Retinal space within which incoming light can alter the firing pattern of a neuron

Photoreceptors have a small circular space surrounding it - receptive field

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4
Q

Define convergence

A

Number of LOWER ORDER neurons field synapsing on the SAME HIGHER ORDER neuron (RGC)

RGC receive input from neighbouring photoreceptors (convergence)

ONENOTE!

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5
Q

Convergence of rods vs. cones?

A

Cone system has a LOWER ORDER of covergence than the rod system
o cones tend to be one-to-one
o many rods tend to link to a single RGC

Cone system convergence «<
rods system convergence

ONENOTE!!

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6
Q

Convergence of central retina vs. peripheral retina?

A

Central retina convergence «< peripheral retina covergence

As centra of fovea has highest [RGC] (more cones, NO rods)
o the further away, the MORE photoreceptors feed into ONE RGC

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7
Q

What does low convergence mean?

A

o SMALL receptive field
o FINE visual acuity
o LOW light sensitivity

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8
Q

What does high convergence mean?

A

o LARGE receptive field
o COURSE visual acuity
o HIGH light sensitivity

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9
Q

What are RGCs split into?

A

ON-centre & OFF-centre cells

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10
Q

ON-centre ganglionic cells?

A

Stimulated by light at the CENTRE of the receptive field

Inhibited by light on the EDGE of the receptive field

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11
Q

OFF-centre ganglionic cells?

A

Inhibited by light at the CENTRE of the receptive field

Stimulated by light on the EDGE of the receptive field

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12
Q

Why is the On- & Off-centre ganglion cells important?

A

Important for
o contrast sensitivity
o edge detection

ONENOTE!!!

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13
Q

Important of Optic Chiasma?

A

53% of fibres decussate here

Lesions ANTERIOR affect SINGLE eyes only
Lesions POSTERIOR affect BOTH eyes

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14
Q

Crossed and uncrossed fibres in the optic chiasma?

A

Crossed fibres
o originate from NASAL retina
o responsible for TEMPORAL visual field

Uncrossed fibres
o originate from TEMPORAL retina
o responsible for NASAL visual field

ONENOTE!!

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15
Q

Visual defects in relation to the optic chiasm?

A

Lesion AT optic chiasma
o damages crossed RGC fibres from nasal retina in both eye
o SO temporal deficit in BOTH eyes
o i.e. BITEMPORAL HEMIANOPIA

Lesion POSTERIOR to optic chiasma
o Right-sided lesion = left HOMONYMOUS HEMIANOPIA in both eyes
o Left-sided lesion = right homonymous hemianopic in both eyes

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16
Q

Disorders of Visual Pathway?

ONENOTE!!

A

If doesn’t cross vertical line - neurological disorder
If doesn’t cross the horizontal line - eye problem (e.g. glaucoma)

The further the lesion is at the back, the smaller the visual defect will be UNLESS its a proper damage that affects the whole tract

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17
Q

Causes of Bitemporal Hemianopia?

A
  • enlargement of PG tumour
    o sits UNDER optic chiasma
    o pushes against it
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18
Q

Causes of Homonymous Hemianopia?

A

Stroke (cerebrovascular accident)

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19
Q

Macular sparing?

A

LOSS of peripheral vision
BUT
RETAIN central acuity

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20
Q

Another name for Primary Visual Cortex?

A

Striate cortex

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21
Q

Where is the 1o Visual Cortex situated and how can you identify it?

A

Along the Calcarine Fissure

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

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22
Q

Explain the representation of different part of the 1o visual cortex

A

DISPROPORTIONATELY large area representing the macula
o due to higher density of RGCs (lower convergence)

Superior visual field
o projects BELOW the Calcarine fissure

Inferior visual field
o projects ABOVE the Calcarine fissure

Left hemi-field (from BOTH eyes)
o projects to the R 1o visual cortex

Right hemi-field (from BOTH eyes)
o projects to the L 1o visual cortex

23
Q

Organisation of the 1o Visual Cortex?

A

Organised as COLUMNS
o unique sensitivity to visual stimulus of a particular orientation

R & L dominant columns intersperse each other (ONENOTE!!)

24
Q

Macular Sparing Homonymous Hemianopia?

A

Damage to PRIMARY VISUAL CORTEX

o often due to stroke
o leads to contralateral homonymous hemianopia w. macula sparing

Area representing the Macula recieves dual-blood supply from Posterior Cerebral Arteries from both sides
o SO macula spared!

25
Q

What is the Extrastriate Cortex and its function?

A

Area surrounding then PRIMARY VISUAL CORTEX

Converts
 o basic visual information
 o orientation
AND
 o position
into complex information!
26
Q

Explain the 2 pathways of the Extrastriate Cortex

A

DORSAL pathway
o 1o visual cortex –> posterior parietal cortex
o MOTION detection, visually-guided action
o Damage results in motion blindness

VENTRAL pathway
o 1o visual cortex –> Inferiotemporal cortex
o OBJECT representation, FACE recognition, detailed FINE CENTRAL vision & COLOUR vision
o Damage results in CEREBRAL ACHROMATOPSIA

27
Q

Pupillary Function?

A

Regulated light input into the eye

28
Q

Pupillary function in LIGHT?

A

Pupil CONSTRICTION

o decreases spherical aberrations & glare
o increases depth of field
o reduces bleaching of photopigments

Mediated by PNS nerve (within CN III)

29
Q

Pupillary function in DARK?

A

Pupil DILATION

o allows MORE light into eye

Mediated by SNS nerve!

30
Q

Pupillary Reflex - Afferent PATHWAY?

A
  1. Rod & Cone photo receptors –> Bipolar cells –> RGCs
  2. Nerves exit at POSTERIOR 1/3 of optic tract
  3. Enter LGN
  4. Synpase at brainstem (pretectal nucleus)
    - synpase on Edinger-Westphal Nuceli on both sides

ONENOTE!! (Red & Green!)

CN II (optic nerve!)

31
Q

Pupillary Reflex - Efferent PATHWAY?

A
  1. Edinger-Westphal Nuclei —> CN III efferenet (oculomotor nerve)
  2. Synpases at ciliary ganglion
  3. To the short POSTERIOR ciliary nerve
  4. To the Pupillary Sphincter

ONENOTE!! (Blue!)

32
Q

Direct vs. Consensual Reflex?

A

Note that the afferent pathway on either eye stimulates the efferent pathways in BOTH eyes

Direct light reflex
o constriction of pupil of the LIGHT-stimulated eye

Consensual light reflex
o constriction of pupil of OTHER eye

33
Q

Right Afferent Defect?

A

Damage to CN II (optic nerve)

When R-eye stimulated
o NO pupil constriction in both eyes

When L-eye stimulated
o NORMAL pupil constriction in BOTH eye

34
Q

Right Efferent Defect?

A

Damage to RIGHT CN III (oculomotor)

NO R-pupil constriction AT ALL

L-eye constricts whether L or R is stimulated

35
Q

Unilateral Afferent Defect?

A

Difference in response pending on which eye is stimulated

36
Q

Unilateral Efferent Defect?

A

SAME UNEQUAL response between L & R eye irrespective which eye is stimulated

37
Q

How do you demonstrate the weakness of the afferent pathway?

A

Swinging Torch Test!

RAPD - relative afferent pupillary defect

The damage to the afferent pathway is usually incomplete of relative
o partial pupillary reponse still present when the damaged eye is stimulated

E.g. RAPD in R-eye
o BOTH eyes constrict when light swings to L-eye with intact pathway

o BOTH pupils will PARADOXICALLY DILATE when light swings to R-eye
- as a result of relatively reduced drive for pupillary constriction in both eyes

38
Q

Muscle and CN associated with eye movemenbt?

A

6 EXTRAOCULAR muscles

Innervated by 3 CN’s

39
Q

Eye Movement terminology?

A

Duction
o eye movement in ONE eye

Version
o eye movement in BOTH eyes in the SAME direction
o dextro- = to the R
o levo- = to the L

Vergence
o eye movement in BOTH eyes in the OPPOSITE direction

Convergence
o Simultaneous adduction (inwards) movement in BOTH eyes
o when viewing a near object

40
Q

Eye speed terminology?

A

Saccade
o short, fast burst of movement (900deg/sec)
o inc. reflexive/scanning/predictive/memory-guided saccade

Smooth pursuit
o sustained slow movement (60deg/sec)
o driven by motion of moving target across the retina

41
Q

Muscles of the Eye?

A

Extraocular muscles - 6!

o attach eyeball to orbit
o straight and rotary movement

42
Q

2 classifications the muscles of the eye are split into?

A

STRAIGHT muscles

AND

OBLIQUE muscles

43
Q

Straight muscles of the eye?

A

4!

  1. Superior rectus

o moves eye UP
o attached to eye at superior
o CN III (occulomotor) innervation

  1. Inferior rectus

o moves eye DOWN
o attached to eye at inferior
o CN III innervation

  1. Medial rectus (or internal rectus)

o attached on the nasal side of the eye
o moves eye TOWARDS MIDDLE of the head (toward the nose)
o CN III innervation

  1. Lateral rectus (or external rectus)

o attached on the temporal side of the eye
o moves eye TOWARDS OUTSIDE of the head (toward temple)
o CN VI (abducens) innervation

44
Q

Oblique muscles of the eye?

A

2!

  1. Superior oblique

o attached HIGH on the temporal side of the eye
o passes UNDER the superior rectus!
o moves eye DOWN & IN
o CN IV (trochlear) innervation

  1. Inferior oblique

o attached LOW on the nasal side of the eye
o passes OVER the inferior rectus
o moves eye UP & OUT
o CN III innervation

45
Q

Which 3 CNs innervate the 6 extraocular muscles?

A

CN III - occulomotor

CN IV - trochlear

CN VI - abducens

46
Q

How does CN III innervate the extraocular muscles?

A
  1. SUPERIOR branch

o Superior rectus = ELEVATES eye (abd)
o Lid Levator = RAISES eyelid

  1. INFERIOR branch

o Inferior rectus = DEPRESSES eye (abd)
o Medial rectus = ADDUCTS eye
o Inferior oblique = ELEVATES eye (add)
o PNS nerve = CONSTRICTS pupil

47
Q

How does CN IV innervate the extraocular muscles?

A

Superior Oblique - DEPRESSES eye (add)

48
Q

How does CN VI innervate the extraocular muscles?

A

Lateral rectus - ABDUCTS eye

49
Q

Abduct vs. Adduct?

A

Abduct = AWAY from midline

Adduct = TOWARDS midline

ONENOTE (eye w. CNs!!)

50
Q

How to test eye movement?

A

Muscles must be isolated to test nerve & muscle function

51
Q

3rd nerve palsy?

A

Affected eye - DOWN & OUT
o eyelid DROOPS
o eye droops

As CN III affected
o unopposed lateral rectus (CN VI) takes over (abducts - out)
o unopposed superior oblique (CN IV) takes over (down)

52
Q

6th nerve palsy?

A

Affected eye can NOT
o abduct

SO deviates to the midline (adducts)

Double-vision worsens on gazing to the side of the affected eye

53
Q

Optokinetic Nystagmus Reflex?

A

Nystagmus = oscillatory eye movement

SO

Optokinetic nystagmus = smooth pursuit + fast-paced reset saccade

Reflex used to test
o visual acuity in pre-verbal children by observing presence of nystagmus movement
o if reflex present means physiological & sign the child DOES HAVE visual acuity to perceive motion

Year 2 - Neuroscience (18 decks)

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