Visual Pathway - Part 1

Question 1

What are the visual pathway landmarks?

Answer 1

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

Question 2

What are the first second and third order neurones?

Answer 2

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

Question 3

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

Answer 3

Optic radiation, from lateral geniculate nucleus to primary visual cortex

Question 4

What is the receptor field of a photoreceptor?

Answer 4

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

Question 5

What is convergence?

Answer 5

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

Question 6

Compare cone and rod convergence

Answer 6

Cone system convergence > rod system convergence

Question 7

Compare central and peripheral retinal convergence

Answer 7

Central retinal convergence > peripheral retinal convergence

Question 8

Describe the features of low convergence

Answer 8

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

Question 9

Describe the features of high convergence

Answer 9

Large receptor fields
High light sensitivity
Coarse visual acuity

Question 10

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

Answer 10

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

Question 11

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

Answer 11

Better contrast sensitivity

Enhanced edge detection

Question 12

What do lesions anterior to the optic chiasm affect?

Answer 12

One eye only

Question 13

What do lesions posterior to the optic chiasm affect?

Answer 13

Both eyes, due to crossing over

Question 14

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

Answer 14

Temporal visual field

Nerves originate from nasal side

Question 15

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

Answer 15

Bitemporal hemianopia

Question 16

Where would the lesion be in homonymous hemianopia/

Answer 16

On either the left or right optic tract or occipital lobe

Question 17

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

Answer 17

LEFT homonymous hemianopia

And vice versa.

Question 18

Give a cause of bitemporal hemianopia

Answer 18

Pituitary adenoma, as pituitary sits underneath optic chiasm

Question 19

Give a cause of homonymous hemianopia

Answer 19

CVA e.g. stroke

Question 20

What is another name for the primary visual cortex?

Answer 20

Striate cortex

Question 21

Where is the primary visual cortex?

Answer 21

Situated along calcarine sulcus within occipital lobe

Question 22

Describe the representation of the macula in the striate cortex

Answer 22

It’s disproportionately largely represented

Question 23

Where does the superior visual field project in the cortex?

Answer 23

BELOW calcarine fissure

Question 24

Where does the inferior visual field project in the cortex?

Answer 24

ABOVE calcarine fissure

Question 25

What projects to the left primary visual cortex?

Answer 25

RIGHT hemifield from both eyes

Question 26

What projects to the right primary visual cortex?

Answer 26

LEFT hemifield from both eyes

Question 27

How is the primary visual cortex organised?

Answer 27

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

Question 28

What is often spared in homonymous hemianopia and why?

Answer 28

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

Question 29

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

Answer 29

The area surrounding the primary visual cortex | Converts basic visual info, orientation and position into complex info

Question 30

What are the two pathways from the extrastriate cortex?

Answer 30

Dorsal pathway | Ventral pathway

Question 31

What is the dorsal pathway from the extrastriate cortex?

Answer 31

Primary visual cortex to posterior parietal cortex (WHERE)

Question 32

What is the ventral pathway from the extrastriate cortex?

Answer 32

Primary visual cortex to inferiotemporal cortex (WHAT)

Question 33

What is the ventral pathway needed for?

Answer 33

Object recognition Facial recognition Detailed central vision Colour vision

Question 34

What is the dorsal pathway needed for?

Answer 34

Motion detection | Visually guided actions

Question 35

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

Answer 35

Damage to dorsal pathway: motion blindness | Damage to ventral pathway: cerebral achromatopsia

Question 36

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

Answer 36

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

Question 37

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

Answer 37

CN 3

Question 38

Describe the afferent pathway of the pupil reflex

Answer 38

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

Question 39

Describe the efferent pathway of the pupil reflex

Answer 39

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

Question 40

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

Answer 40

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

Question 41

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

Answer 41

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

Question 42

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

Answer 42

Efferent

Question 43

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?

Answer 43

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

Question 44

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

Answer 44

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