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Neuro > Visual Pathways > Flashcards

Visual Pathways Flashcards

1
Q

What are the retinal neural layers?

A

Outer - Photoreceptors

Middle - Bipolar cells (Improve contrast, regulate sensitivity)

Inner - Retinal ganglion cells

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2
Q

Where do visual stimuli travel?

A

Eye
Optic nerve
Optic chiasm (53% fibres cross)
Optic tract - ganglion nerve fibres exit as this
Lateral Genticulate nucleus - ganglion nerve fibres synapse here (in thalamus)
Optic Radiation - 4th order neuron
Primary visual cortex (Striate Cortes) - Within occidental lobe
Extrastiate cortex

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3
Q

What is a visual receptive field?

A

retinal space within which incoming light alters firing pattern of a neurone

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4
Q

What is receptive field convergence?

A

Convergence of receptive field - number of lower order neurone fields synapsing on a single higher order neurone

Cone convergence > Rod divergence
Central convergence > Peripheral divergence

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5
Q

What are on and off centre ganglion cells?

A

On centre ganglion cells - stimulated by light at centre of receptive field, inhibited by light at periphery

Off centre ganglion cells - Inhibited by light at centre of receptive field, stimulated by light at periphery

Helps contrast sensitivity and edge detection

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6
Q

What is the optic chiasma

A

Point where the optic nerves cross

Lesions anterior to chiasma - ipselateral defect

Lesions posterior to chiasma - bilateral defect
(Right-sided lesion: left homonymous hemianopia
Left-sided lesions: right homonymous hemianopia)

Lesion ON chiasma - Bitemporal hemianopia

Crossed fibres from nasal retina responsible to temporal visual field
Uncrosses fibres from temporal retina responsible for nasal visual field

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7
Q

Describe the primary visual cortex

A

Along Calcarine sulcus - occipital lobe
Distinct stripe - myelinated optic radiation fibre

Representation
Macula disproportionate large
Superior visual field projects to below calcarine fissure
Inferior visual field projects to above calcarine fissure
Ipsilateral hemifield respresentation for both eyes
(left from both eyes goes to right)

Organised with columns (right and left dominant interspersed) sensitive to particular orientation. Allows depth perception

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8
Q

Explain Macular sparing homonymous hemionopia

A

Macula representing area has dual blood supply - Post cerebral arteries. In stroke one blood suply usually unaffected - Macula function spared

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9
Q

Describe the extrastriate cortex

A

Around primary cortex in occipital lobe
Converts visual info into position info

Dorsal pathway - Motion detection, visual guided action, projects to post parietal cortex
Ventral pathway - Object and face recognition, detail and colour vision, projects to inferiotemporal cortex

damage causes cerebral achromatopsia

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10
Q

What is the function of the Pupillary reflex?

A

Regulate light input (less than 2 log unit change)

In light - decreases glare and spherical aberrations, reduces photo-bleaching CN III mediated

In dark - Increases light sensitivity, sympathetic mediated

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11
Q

What is the afferent pathway of the pupillary reflex?

A

Rod and cone cells -> Bipolar cells -> Retinal ganglion cells

Pupil specific ganglion cells -> exit post 1/3 of optic tract -> Lateral geniculate nucleus

Lateral geniculate nucleus -> pretectal nucleus in brainstem

Pretectal nucleus-> interneurones -> edinger-westphal

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12
Q

What is the efferent pathway of the pupillary reflex?

A

Edinger-westphal -> Occulomotor nerve -> ciliary ganglion -> Short post ciliary nerve -> pupillary sphincter

Direct and consensual reflex in physiology

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13
Q

What do defects in the afferent and efferent pupillary reflex pathways cause?

A

Afferent defect - No response in either eye if light in eye with defect Direct and consensual reflex if light in eye without defect

Efferent defect - Defect eye will not respond directly or consensually. Non defect eye responds directly and consensually

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14
Q

How is Relative Afferent Pupillary Defect tested?

A

Swinging torch - Pardox pupil dilation in defective eye in non-complete damage. This is because the constriction response elicited by the bad eye is weaker than the consensual response elicited by the good eye

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15
Q

What happens as the retinal ganglion cells enter the optic nerve, which improves the transmission of the signal?

A

They become myelinated

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16
Q

Describe the convergence and receptive field sizes of rods and cones.

A

Rods have high convergence and large receptive fields Cones have low convergence and small receptive fields

17
Q

Describe how the convergence of the rod system differs across different parts of the retina.

A

The rod system near that macula has lower convergence than in the peripheral retina

18
Q

What is the benefit of having high or low convergence and a large or small receptive field?

A

High, large - High light sensitivity

Low, small - Fine visual acuity

19
Q

Which part of the brain does the upper division of the optic radiation travel through and which parts of the visual field is it responsible for?

A

Parietal Lobe Responsible for the inferior visual quadrants

20
Q

Which part of the brain does the lower division of the optic radiation travel through and what part of the visual field is it responsible for?

A

Temporal Lobe Responsible for the superior visual quadrants

21
Q

The lower division loops inferiorly and anteriorly before going posteriorly towards the primary visual cortex. What is this loop called?

A

Meyer’s Loop

22
Q

What would be the consequence of a lesion in Meyer’s loop?

A

Superior homonymous quadrantopia

23
Q

What would be the consequence of a lesion of the upper division of the optic radiation?

A

Inferior homonymous quadrantopia

24
Q

What is homonymous hemianopia typically caused by?

A

Strokes and other cerebrovascular accidents

25
Q

What are the Types of eye movement?

A

Duction - unilateral eye movement

Version - simultaneous same direction movement of eyes

Vergence - simultaneous opposite direction movement of eyes

Convergence - Simultaneous adduction of both eyes in near vision

26
Q

What are the speeds of eye movement?

A

Saccade - short fast 900 deg/sec

  • Reflexive
  • Scanning
  • Predictive to track object
  • Memory guided

Smooth persuit - sustained slow (up to 60 deg/sec)
- Accurate tracking

27
Q

What is the term for the elevation of one eye?

A

Supraduction

28
Q

What is the term for the depression of both eyes?

A

Infraversion

29
Q

What is the technical term for right gaze?

A

Dextroversion

30
Q

What is the technical term for left gaze?

A

Levoversion

31
Q

What reflex is used to assess visual acuity in preverbal children?

A

Optokinetic Nystagmus Reflex It is a form of physiological nystagmus triggered by the presentation of a constantly moving grating pattern

32
Q

What are the Six extraocular muscles?

A

Superior oblique - moves down and in (CN IV)

Inferior oblique - moves up and out (CN III inf branch)

Superior rectus - moves up (CN III sup branch)

Inferior rectus - move down (CN III Inf branch)

Lateral rectus - moves out (CN VI)

Medial rectus - move in (CN III inf branch)

33
Q

How would you test the extraocular muscles?

A

Isolate the muscle to be tested by maximising its action and minimising the action of the other muscles E.g. to test the superior rectus, make the patient abduct and elevate their eye

34
Q

Describe the CN III, IV and VI nerve palsys

A

Third nerve palsy - down (unopposed CN IV) and out (unnoposed CN VI), ptosis

Sixth nerve palsy - affected eye deviate inwards, double vision when looking to side

Fourth nerve palsy - upwards (Unopposed CN III) double vision looking down

35
Q

What is Hering’s Law of Equal Innervation?

A

Muscles from both eyes involved in conjugate movement receive equal innervation

36
Q

What structure in the brainstem acts as a synchronising link between the eyes, allowing paired eye movements?

A

Medial Longitudinal Fasciculus

37
Q

What can damage to the MLF cause?

A

Internuclear Opthalmoplegia

E.g. right abduction wont be accompanied by left adduction Could be accompanied by nystagmus on right gaze

38
Q

What is Sherrington’s Law of Reciprocal Innervation?

A

Agonist muscles contract while antagonist muscles relax

39
Q

State a condition in which Sherrington’s Law is violated.

A

Duane’s Syndrome – congenital absence of abducens (CN VI) Both lateral and medial recti are innervated by CN III (oculomotor)

Neuro (21 decks)

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