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Year 2 - neuroscience > Neurology of the visual system > Flashcards

Neurology of the visual system Flashcards

1
Q

What is the complete visual pathway?

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 – ganglion fibres synapse in nucleus
  6. Optic radiation – 4th order neuron
  7. Primary visual cortex (lower visual processing) or striate cortes -> extrastriate cortex (higher processing)
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2
Q

What is the visual pathway from the retina?

A
  1. First order neurones (R+C)
  2. Second order neurones (retinal bipolar)
  3. Third order neurones (retinal ganglion cells)
  4. Optic nerve
  5. Partial decussation at chiasmd (53% of fibre)
  6. Optic tract
  7. Synpase at lateral geniculate nucleus in thalamus
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3
Q

What happens to retinal ganglion fibres to improve signal transmission?

A

They become myelinated after entering the optic nerve

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4
Q

What is the receptive field of a neurone?

A

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

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5
Q

Compare the receptive fields of a single photoreceptor compared to a ganglion cell

A

In the case of a single photoreceptor, any light that falls within its immediate neighbourhood on the retina, will excite the photo-receptor.

The receptive field of ganglion cells covers a much larger area than that of a single photoreceptor.

It includes the receptive fields of all the photoreceptors, that synapse upon the ganglion cells indirectly via bipolar cells.

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6
Q

What is convergence?

A

Number of lower order neurons synapsing on the same higher order neuron.

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7
Q

Compare cone and rod system convergence

Compare central retinal and peripheral retinal convergence

A

Cone system convergence < Rod system convergence

Central retina convergence < peripheral retinal convergence

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8
Q

What does a low convergence mean?

- effect on receptive field, visual acuity and light sensitivity

A
  • Small Receptive Field
  • Fine Visual Acuity
  • Low Light Sensitivity
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9
Q

What does a high convergence mean?

- effect on receptive field, visual acuity and light sensitivity

A
  • Large Receptive Field
  • Coarse Visual Acuity
  • High Light Sensitivity
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10
Q

What are on and off centre ganglion cells?

A

On-centre Ganglion: Stimulated by light at the centre of the receptive field. Inhibited by light on the edge of the receptive field

Off-centre Ganglion: Inhibited by light at the centre of the receptive field. Stimulated by light on the edge of the receptive field.

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11
Q

What are on and off centre ganglion cells important for?

A

Contrast sensitivity and enhanced edge detection

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12
Q

How will lesions before and after the optic chiasm differ in their effects on vision?

A
  • Lesions anterior to optic chiasm affect visual field in one eye only
  • Lesions posterior to optic chiasm affect visual field in both eyes
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13
Q

Which are the crossed and uncrossed fibres at the optic chiasm?

A

Crossed Fibres – originating from nasal retina, responsible for temporal visual field

Uncrossed Fibres – originating from temporal retina, responsible for nasal visual field

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14
Q

What will lesions at the optic chiasm cause?

A
  • Damages crossed ganglion fibres from nasal retina in both eyes

Temporal field deficit in both eyes – bitemporal hemianopia

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15
Q

What will lesions posterior to the optic chiasm cause?

A

Right sided lesion – left homonymous hemianopia in both eyes

Left sided lesion – right homonymous hemianopia (half eye blindness) in both eyes

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16
Q

What are some visual defects?

A
  • monocular blindness (one eye)
  • bitemporal heminanopia
  • right nasal hemianopia
  • homonymous hemianopia
  • quadrantanopia
  • macular sparing (macula - central - vision spared)
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17
Q

What causes bitemporal hemianopia and homonymous hemianopia?

A

Bitemporal Hemianopia
- Typically caused by enlargement of pituitary gland tumour pressing on optic chiasm from below
(pituitary gland sits under optic chiasm)

Homonymous Hemianopia

  • Stroke
  • Cerebrovascular accidents
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18
Q

How is vision loss different in glaucoma and neurological conditions?

A

Glaucoma often affects the horizontal plane of loss of vision

Neurological problems often affect the vertical plane of loss of vision

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19
Q

Where is the primary visual cortex?

A
  • Situated along calcarine sulcus within occipital lobe
  • Also known as striate cortex
  • Characterized by a distinct stripe derived from the myelinated fibre of the optic radiation projecting into the visual cortex
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20
Q

What is represented within the visual cortex?

A
    • Disproportionately large area representing the macula
  • Superior visual field projects to below the calcarine fissure
  • Inferior visual field projects to above the calcarine fissure
  • The right hemifield from both eyes projects onto left PVC
  • The left hemifield from both eyes projects onto right PVC
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21
Q

What is the role of the PVC?

A

Processing visual information of static and moving objects

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22
Q

How is the PVC organised?

A
  • Organized as columns
  • Each column is sensitive to a visual stimulus of a particular orientation
  • Right eye and left dominant columns intersperse each other
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23
Q

What is macular sparing homonymous hemianopia?

A
  • Caused by damage to primary visual cortex
  • Often due to stroke
  • Leads to contralateral MSHH
  • Macula is spared as it has dual blood supply from the L/R posterior cerebral arteries
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24
Q

Where and what is the extrastriate cortex?

A
  • Area around PVC within the occipital lobe

- Converts basic visual information, orientation and position into complex information

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25
Q

What is the dorsal pathway (how pathway) in the PVC?
What does it detect?
What does damage lead to?

A
  • PVC -> posterior parietal cortex
  • Motion detection, visually-guided action
  • Damage results in motion blindness
26
Q

What is the ventral pathway (the what pathway) in the PVC?
What does it detect?
What does damage lead to?

A
  • PVC -> inferiotemporal cortex
  • Object representation, face recognition
  • Detailed fine central vision and colour vision
  • Damage may result in cerebral achromatopsia (partial/total loss of colour vision)
27
Q

What happens to the eye in the light?

A
  • constricts due to the circular iris muscle contracting:
  • decreases spherical aberrations and glare
  • increases depth of field and reduces amount of light entering the eye
  • reduces bleaching of photopigments

PUPIL CONSTRICTION BY CN 3 PNS

28
Q

What happens to the eye in the dark?

A
  • pupil dilates: radial muscle contracts
  • more light into eye
  • sympathetic nerve
29
Q

What is the afferent pathway in the pupillary reflex?

A

Rod and cone photoreceptor -> bipolar cells -> RGCs -> nerves exit at posterior 1/3rd of optic tract and enter LGN -> synapse at brainstem (Pretectal nucleus) -> synapse at Edinger Westphal nucleus

30
Q

What is the efferent pathway in the pupillary reflex?

A

Edinger Westphal -> oculomotor nerve efferent -> synapse at ciliary ganglion -> short posterior ciliary nerve -> pupillary sphincter (BOTH EYES)

31
Q

What is the direct light reflex?

A

constriction of pupil of the light stimulated eye

32
Q

What is the consensual light reflex?

A

constriction of pupil of the other eye

33
Q

What happens if there is a right afferent defect e.g. optic nerve damage?

A

No pupil constriction in both eyes when right eye is stimulated with light

Normal pupil constriction in both eyes when left eye is stimulated with light

34
Q

What happens if there is a right efferent defect e.g. right oculomotor nerve damage?

A

No right pupil constriction whether right or left eye is stimulated with light

Left pupil constricts whether right or left eye is stimulated with light

35
Q

What is the swinging torch test?

A
  • Done to demonstrate weakness of the afferent pathway

- The damage is usually incomplete or relative

36
Q

What will happen in the swinging torch test if there is a relative afferent pupillary defect in the right eye?

A
  • Partial pupillary response still present when the damaged eye is stimulated
  • Elicited by the swinging torch test – alternating stimulation of right and left eye with light
  • Both pupils constrict when light swings to left undamaged side
  • Both pupils paradoxically dilate when light swings to the right damaged side
37
Q

What is duction, version, vergence and convergence?

A

Duction – eye movement in one eye

Version – eye movement in both eyes in the same direction, dextroversion is to the right, levo- is to the left

Vergence – eye movement in both eyes in opposite directions

Convergence – simultaneous adduction (inwards) movement in both eyes when viewing a near object

38
Q

What is saccade and smooth pursuit?

A

Saccade – short, fast burst of movement (900deg/second) – reflexive saccade, scanning saccade, predictive saccade and memory-guided saccade

Smooth pursuit – sustained slow movement (60deg/second) – driven by motion of a moving target across the retina

39
Q

What are the 6 extraocular muscles?

A
  • Attach eyeball to orbit
  • straight and rotatory movements
  • 4 straight: superior, inferior, medial and lateral rectus
  • superior and inferior oblique muscles
40
Q

Where are the superior and inferior rectus attached and what do they do?

A

Superior rectus Attached to the eye at 12 o’clock, moves the eye up and adduct

Inferior rectus Attached to the eye at 6 o’clock, moves the eye down and adduct

41
Q

Where is the lateral rectus attached and what does it do?

A
  • It attaches on the temporal side of the eye

- It moves the eye toward the outside of the head (toward the temple

42
Q

Where is the medial rectus attached and what does it do?

A
  • It attaches on the nasal side of the eye

- It moves the eye toward the middle of the heard (towards the nose)

43
Q

Where is the superior oblique muscle attached and what does it do?
What does it pass under and what is it innervated by?

A
  • Attached high on the temporal side of the eye
  • Passes under the superior rectus
  • Moves the eye down and in
  • Trochlea
44
Q

Where is the inferior oblique attached, what does it do, what does it pass and what is it innervated by?

A
  • Attached low on the nasal side of the eye
  • Passes over the inferior rectus
  • Moves the eye up and out
  • Occulomotor innervation
45
Q

What innervates the superior and inferior rectus muscles?

A

superior - superior occulomotor nerve

inferior - inferior occulomotor

46
Q

What innervates the medial rectus?

A

inferior occulomotor

47
Q

What innervates lid levator?

A

superior occulomotor

48
Q

What innervates the inferior oblique?

A

inferior occulomotor

49
Q

What innervates the superior oblique?

A

fourth cranial nerve

50
Q

What innervates the lateral rectus?

A

sixth cranial nerve

51
Q

How can the eye movements be tested?

A

Abduction – Lateral Rectus

Adduction – Medial Rectus

Elevated and Abducted – Superior Rectus

Depressed and Abducted – Inferior Rectus

Elevated and Adducted – Inferior Oblique

Depressed and Adducted – Superior Oblique

52
Q

What is supraversion?

A

The elevation of both eyes, namely simultaneous right and left eye supraduction.

53
Q

What is infraversion?

A

Depression of both eyes, namely simultaneous right and left eye infraduction.

54
Q

What is abduction and adduction?

A

Abduction refers to duction movement of one eye, moving away from the nose. Adduction refers to duction movement of one eye, moving towards the nose.

55
Q

What is dextroversion and levoversion?

A

Dextroversion involves simultaneous right eye abduction, and left eye adduction.

Levoversion involves simultaneous left eye abduction, and right eye adduction.

56
Q

What is supraduction and supraversion?

A

Up (Elevation): Supraduction – one eye

Supraversion – both eyes

57
Q

What is torsion?

A

rotation of eye around the anterior-posterior axis of the eye

58
Q

What is third nerve palsy?

A

Only muscles not innervated by CN III in the affected eye are working

  • Lateral rectus muscle and superior oblique muscle
  • Affected eye down and out
  • Droopy eyelid (ptosis)
  • Unopposed superior oblique innervated by fourth nerve (down)
  • Unopposed lateral rectus action innervated by sixth nerve (out)
59
Q

What is sixth nerve palsy?

A
  • Sixth nerve palsy presents with deficit in abduction in the affected eye
  • This is made apparent when the patient is asked to abduct the affected eye
  • The affected eye deviates inwards (unable to abduct)
  • Double vision worsen on gazing to the side of affected eye
60
Q

What is optokinietic nystagmus reflex?

A

Oscillatory eye movement

- smooth and fast paced movement between two points

61
Q

What is optokinietic nystagmus useful for?

A

To test visual acuity in pre-verbal children by observing presence of nystagmus movement
- reflex is physiological and shows they can percieve motion

Year 2 - neuroscience (13 decks)

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