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Y2 Neuroscience and Mental Health > The Neurology of the Visual System > Flashcards

The Neurology of the Visual System Flashcards

1
Q

Describe the route of the visual pathway

A
  1. Eye
  2. Optic Nerve – Ganglion Nerve Fibres
  3. Optic Chiasm – Half of the nerve fibres cross here
  4. Optic Tract – Ganglion nerve fibres exit as optic tract
  5. Lateral Geniculate Nucleus – Ganglion nerve fibres synapse at Lateral Geniculate Nucleus
  6. Optic Radiation – 4th order neuron
  7. Primary Visual Cortex or Striate
    Cortes – within the Occipital Lobe
  8. Extrastriate Cortex
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2
Q

What are the first, second and third order neurons form the retina

A

First Order Neurons – Rod and Cone Retinal Photoreceptors

Second Order Neurons – Retinal Bipolar Cells

Third Order Neurons – Retinal Ganglion Cells

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3
Q

Describe the retinal ganglion cells

A 
Optic Nerve (CN II)
Partial Decussation at Optic
Chiasma – 53% of ganglion
fibres cross the midline – Optic Tract
Travels to. Lateral Geniculate Nucleus (LGN) in Thalamus – to relay visual information to Visual Cortex
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4
Q

What is the receptive field

A

Retinal space within which incoming light can alter the firing pattern of a neuron
Photoreceptor – a small circular space surrounding the photoreceptor
Retinal Ganglion Cell
– Inputfrom neighbouring photoreceptors (convergence)

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5
Q

What is convergence

A

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

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6
Q

Compare the convergence of cone and rod systems and central vs peripheral retina

A

Cone System Convergence > Rod System Convergence

Central Retina Convergence > Peripheral Retina Convergence

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7
Q

Describe low convergence

A

Small receptive field
Fine visual acuity
Low light sensitivity

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8
Q

Describe high convergence

A

Large receptive field
Coarse visual acuity
High light sensitivity

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9
Q

Describe the on-centre ganglion 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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10
Q

Describe the off-centre ganglion 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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11
Q

What is the importance of retinal ganglion cells

A

Contrast sensitivity

Enhanced edge detection

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12
Q

Describe the optic chiasm

A

53% of ganglion fibres cross here
Crossed fibres originate from the nasal retina, responsible for the temporal visual field.
Uncrossed fibres originate from the temporal retina, responsible for nasal visual field

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13
Q

Describe the affects of lesions o the optic chiasm

A

Anterior to chiasm - one eye only
At the chiasm - Causes bitemporal hemianopia
Posterior to chiasm - visual field in both eyes affected
Right side lesion - left homonymous hemianopia in both eyes

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14
Q

Describe bitemporal hemianopia

A

BitemporalHemianopia
Typically caused by enlargement of Pituitary Gland Tumour
Pituitary Gland sits under Optic Chiasma

Homonymous Hemianopia
Stroke (Cerebrovascular Accident)

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15
Q

Describe 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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16
Q

What projects to the different parts of the primary visual cortex

A

Below calcarine fissure - superior visual field
Above calcarine fissure - inferior visual field
Left primary visual cortex - right hemifield
Right primary visual cortex - left hemifield

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17
Q

What are the functions of the primary visual cortex

A

Organised as columns with unique sensitivity to visual stimulus or a particular orientation
Right eye and left dominant columns intersperse each other

18
Q

Describe the common cause of primary visual cortex damage and what it leads to

A

Often due to stroke
Leads to Contralateral Homonymous Hemianopia with Macula Sparing
Area representing the Macula receives dual blood supply from Posterior Cerebral Arteries from both sides

19
Q

What is the function of the pupil and what is contraction and dilation mediated by

A

Regulates light input to the eye

contraction - parasympathetic (CN III)
dilation - sympathetic

20
Q

What are the effects of pupil constriction

A

Decreases spherical aberrations and glare
Increases depth of field
Reduces bleaching of photo-pigments

21
Q

What are the effects of pupil dilations

A

Increases light sensitivity in the dark by allowing more light in

22
Q

Explain the pupillary reflex

A
  1. Rod and cone photoreceptors synapse on bipolar cells synapsing on retinal ganglion cells
  2. Pupil-specific ganglion cells exist at the posterior 1/3 of the optic tract before entering the lateral geniculate nucleus
  3. Synapses at the brain stem (pretectal nucleus)
  4. Afferent pathway from each eye synapses on the Edinger-Westphal nuclei on both sides in the brainstem
  5. Path to oculomotor nerve efferent
  6. Synapse at ciliary ganglion
  7. Short posterior ciliary nerve -> pupillary sphincter
23
Q

Compare direct to consensual light reflex and explain why this occurs

A

Direct - constriction of the pupil that is light-stimulated
Consensual - constriction of the other eye
Afferent pathway on either side will stimulate efferent pathway on both sides

24
Q

Describe what occurs in a right afferent defect

A

Normal pupil constriction in both eyes when left eye is stimulated with light
No pupil constriction in both eyes when the right eye is stimulated with light
e.g. damage to optic nerve

25
Q

Describe what occurs in a right efferent defect

A

Left eye constricts whether right or left eye is stimulated with light
No right pupil constriction whether right or left eye is stimulated with light
e.g. damage to right 3rd nerve

26
Q

Compare unilateral afferent and efferent defects

A

afferent - difference response pending on which eye is stimulated

efferent - same unequal response between left and right eye irrespective of the eye stimulated

27
Q

Define duction, version, mergence and convergence

A

Duction = Eye Movement in One Eye

Version = Simultaneous movement of both eyes in the same direction

Vergence = Simultaneous movement of both eyes in the opposite direction

Convergence = Simultaneous adduction (inward) movement in both eyes when viewing a near object

28
Q

What is saccade movement

A 
Short, fast burst 
up to 900deg/sec
Reflexive saccade to external stimuli
Scanning saccade
Predictive saccade to track objects
Memory-guided saccade
29
Q

What is smooth pursuit movement

A

Sustained slow movement
Up to 60deg/sec
Driven by motion of a moving target across the retina

30
Q

What are the straight muscles of the eye

A

Superior rectus
Inferior rectus
Medial rectus
Lateral rectus

31
Q

What movements of the eye do the rectus muscles assist in

A

SR - elevation
IR - depression
LR - abduction
MR - adduction

32
Q

Describe the superior oblique muscle

A

Attached on the temporal side of eye
Passes under the superior rectus
Moves the eye down and in
Travels through the trochlea

33
Q

Describe the inferior oblique muscle

A

Passes over the inferior rectus

Moves the eye up and out

34
Q

Which extra ocular muscles does the superior branch of the oculomotor nerve supply

A

Superior rectus - elevates eye

Lid levator - raises eyelid

35
Q

Which extra ocular muscles does the inferior branch of the oculomotor nerve supply

A

Inferior rectus - depression
Medial rectus - adduction
Inferior oblique - elevates eye
Parasympathetic - constricts pupil

36
Q

Which extra ocular muscles does the trochlear nerve supply

A

Superior oblique - depression

37
Q

Which extra ocular muscles does the abducens nerve supply

A

Lateral rectus - abduction

38
Q

What are the directions of eye movement

A

Elevation - supraduction, supraversion
Depression - infraduction, infraversion
Dextroversion (right) - Right adduction, left abduction
Levoversion - Right adduction, left abduction
Torsion - rotation of eye around the anterior-posterior axis of the eye

39
Q

Describe third nerve palsy

A

Down and out movement affected
Droopy eyelid
Unopposed superior oblique innervated by fourth nerve (down)
Unopposed lateral rectus action innervated by sixth nerve (out)

40
Q

Describe sixth nerve palsy

A

Affected eye unable to abduct and deviates inwards

Double vision worsen on gazing to the side of the affected eye

41
Q

What is nystagmus and optokinetic nystagmus

A

Oscillatory eye movement

Smooth pursuit + fast phase rest saccade

42
Q

What is the optokinetic nystagmus reflex useful for

A

testing visual acuity in pre-verbal children
Observe presence of nystagmus movement in response to moving grating patterns of various spatial frequencies
Signifies the patient has sufficient visual acuity to perceive grating pattern

Y2 Neuroscience and Mental Health (22 decks)

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