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Neuro > Visual Pathway - Part 1 > Flashcards

Visual Pathway - Part 1 Flashcards

1
Q

What are the visual pathway landmarks?

A 
Eye
Optic nerve
Optic chiasm 
Optic tract
Lateral geniculate nucleus 
Optic radiation
Primary visual cortex/striate cortices 
Extrastriate cortex
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2
Q

What are the first second and third order neurones?

A

First order- rods and cones
Second order - bipolar neurones
Third order - retinal ganglion cells

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3
Q

What are the fourth order neurones and where do they arise from?

A

Optic radiation, from lateral geniculate nucleus to primary visual cortex

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4
Q

What is the receptor field of a photoreceptor?

A

The retinal space surrounding a photoreceptor, where light falling activates or alters the firing rate of the photoreceptor

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5
Q

What is convergence?

A

The number of lower order neurons (photoreceptors, bipolar neurones) synapsing onto the same higher order neuron (ganglion cell)

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6
Q

Compare cone and rod convergence

A

Cone system convergence > rod system convergence

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7
Q

Compare central and peripheral retinal convergence

A

Central retinal convergence > peripheral retinal convergence

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8
Q

Describe the features of low convergence

A

Small receptor fields
Low light sensitivity
Fine visual acuity (because you can distinguish more finely)

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9
Q

Describe the features of high convergence

A

Large receptor fields
High light sensitivity
Coarse visual acuity

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10
Q

What are the two classifications of retinal ganglion cells. Describe the difference

A

On centre and off centre
On centre - activated by light at centre of receptive field, inhibited by light at periphery
Off centre - stimulated by light at periphery of receptive field, inhibited by light at centre

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11
Q

What are the advantages of having on and off centre ganglion cells?

A

Better contrast sensitivity

Enhanced edge detection

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12
Q

What do lesions anterior to the optic chiasm affect?

A

One eye only

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13
Q

What do lesions posterior to the optic chiasm affect?

A

Both eyes, due to crossing over

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14
Q

Which part of the visual field are the crossed fibres of the optic chiasm responsible for?

A

Temporal visual field

Nerves originate from nasal side

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15
Q

What would result from a lesion just anterior to the optic chiasm?

A

Bitemporal hemianopia

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16
Q

Where would the lesion be in homonymous hemianopia/

A

On either the left or right optic tract or occipital lobe

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17
Q

What would a lesion on the right, posterior to the optic chiasm result in?

A

LEFT homonymous hemianopia

And vice versa.

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18
Q

Give a cause of bitemporal hemianopia

A

Pituitary adenoma, as pituitary sits underneath optic chiasm

19
Q

Give a cause of homonymous hemianopia

A

CVA e.g. stroke

20
Q

What is another name for the primary visual cortex?

A

Striate cortex

21
Q

Where is the primary visual cortex?

A

Situated along calcarine sulcus within occipital lobe

22
Q

Describe the representation of the macula in the striate cortex

A

It’s disproportionately largely represented

23
Q

Where does the superior visual field project in the cortex?

A

BELOW calcarine fissure

24
Q

Where does the inferior visual field project in the cortex?

A

ABOVE calcarine fissure

25
Q

What projects to the left primary visual cortex?

A

RIGHT hemifield from both eyes

26
Q

What projects to the right primary visual cortex?

A

LEFT hemifield from both eyes

27
Q

How is the primary visual cortex organised?

A

As columns with:
a unique sensitivity to a particular orientation
alternate dominant columns for left and right eye

28
Q

What is often spared in homonymous hemianopia and why?

A

Macula is spared because the area which represents the macula has dual blood supply from posterior cerebral arteries from both sides!

29
Q

What is the extrastriate cortex and what does it do??

A

The area surrounding the primary visual cortex

Converts basic visual info, orientation and position into complex info

30
Q

What are the two pathways from the extrastriate cortex?

A

Dorsal pathway

Ventral pathway

31
Q

What is the dorsal pathway from the extrastriate cortex?

A

Primary visual cortex to posterior parietal cortex (WHERE)

32
Q

What is the ventral pathway from the extrastriate cortex?

A

Primary visual cortex to inferiotemporal cortex (WHAT)

33
Q

What is the ventral pathway needed for?

A

Object recognition
Facial recognition
Detailed central vision
Colour vision

34
Q

What is the dorsal pathway needed for?

A

Motion detection

Visually guided actions

35
Q

What do damages to the ventral and dorsal pathways result in?

A

Damage to dorsal pathway: motion blindness

Damage to ventral pathway: cerebral achromatopsia

36
Q

Besides limiting how much light enters the eye, why is pupil constriction important?

A

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

37
Q

Which nerve does the parasympathetic nerve travel with to control pupil constriction?

A

CN 3

38
Q

Describe the afferent pathway of the pupil reflex

A

Rod and cone photoreceptors
Bipolar neurones
Retinal ganglion cells
Optic nerve
Pretectal nucleus of midbrain (same side)
Edinger-Westphal nucleus of midbrain (both sides)

39
Q

Describe the efferent pathway of the pupil reflex

A 
Edinger-Westphal nucleus of midbrain (from both sides)
Occulomotor nerve 
Ciliary ganglion 
Short posterior ciliary nerve 
Pupillary sphincter
40
Q

What would you see when you shine light into both eyes if there was damage to the optic nerve leaving the RIGHT eye?

A

Light shone in right eye: no pupil constriction in both eyes
Light shone in left eye: normal pupil constriction in both eyes

41
Q

What would you see if there was efferent nerve damage to the RIGHT oculomotor nerve?

A

No pupil constriction in right eye, regardless of which eye the light is shone into
Normal constriction of left eye despite which eye the light is shone into

42
Q

If one eye doesn’t constrict regardless of which eye light is shone into, is the damage afferent or efferent?

A

Efferent

43
Q

If there is no pupil constriction when you shine the light into one eye, but both eyes constrict normally when the light is shone into the other eye, where is the lesion?

A

Afferent - side of eye that you shine light into that doesn’t elicit consensual reflex

44
Q

What is the RAPD swinging torch test? Describe where the damage would be in relation to where the light is shone.

A

The point of swinging is to see whether, in comparison to the constricted pupil, there is a paradoxical relative dilation in both eyes when the light swings to the DAMAGED side due to afferent pupillary defect

Neuro (11 decks)

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