C: Ascending visual pathways Flashcards Preview

Year 2 Term 2 C&M > C: Ascending visual pathways > Flashcards

Flashcards in C: Ascending visual pathways Deck (47)
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1
Q

The sclera is a derivative of what?

A

Dura mater

2
Q

At what part of the retina are no photoreceptors located?

A

The optic disc

3
Q

What is the role of the pigmented epithelium in the retina?

A

Sits against the choroid layer and is light absorbing, important in maintaining the metabolic activity of the photoreceptors which it surrounds by the way of melanin filled microvilli
Also provides capillaries to the photoreceptors

4
Q

What kind of energy exchange occurs in the neuronal retina?

A

Light energy - photons

To electrical energy - action potentials

5
Q

How many neurons are in the chain of ascending visual pathway?

A

3

6
Q

What are the 3 neurons in the visual pathway?

A

Note: unlike other pathways all of these neurones are within the CNS
Primary = bipolar cell
Secondary = ganglion cell
Teritary = optic radiation

7
Q

Where do the primary and secondary neurones in the ascending visual pathway synapse?

A

In the inner plexiform layer of the neuronal retina

8
Q

Where do the secondary neurones in the ascending visual pathway synapse?

A

In the lateral geniculate nucleus of the thalamus

9
Q

The axons of ganglion cells in the neuronal retina form what?

A

The optic nerve

10
Q

Via what do neurones travel from the lateral geniculate nucleus of thalamus to the primary visual cortex?

A

The optic radiation

11
Q

Why is the optic nerve considered part of the CNS?

A

Optic nerve is an outgrowth of diencephalon

12
Q

Why can rise in intracranial pressure lead to papilloedema?

A

Optic nerve as part of CNS is surrounded by meninges and has subarachnoid space with CSF within it
Rise in intracranial CSF pressure = rise in CSF pressure surrounding optic nerve
Increase in pressure compresses the central retinal vein preventing venous drainage from the eye = pailloedema

13
Q

How does papilloedema appear on fundoscopy and why?

A

Halo of palor surrounding the optic disc as CSF is being forced against the back of the retina, lifting the retina away from the pigmented epithelium and underlying choroid plexus - thus ring of palor

14
Q

What carries neurones from the retina to the optic chiasm?

A

Optic nerve

15
Q

What carries secondary neurones from the optic chiasm to the lateral geniculate nucleus of the thalamus?

A

Optic tract

16
Q

What carries tertiary neurones from the lateral geniculate nucleus to the primary visual cortex?

A

Optic radiation

17
Q

The primary visual cortex is located where, which surface of the brain can it be seen from?

A

In the occipital lobe either side of the calcarine sulcus - striate cortex (seen mainly from the medial surface, also includes the occipital pole seen from the lateral surface)

18
Q

Where is the visual association area located?

A

Medial occipital lobe (small part of lateral) either side of the striate cortex

19
Q

Info from which parts of the visual fields decussates at the optic chiasm?

A

Info from the temporal parts of visual fields decussates at optic chiasm

20
Q

Info from the left parts of each visual field projects to which cerebral hemisphere?

A

The right cerebral hemisphere and visa versa

21
Q

Info from the periphery of the visual fields presents to which parts of the striate cortex?

A

To the rostral part of the striate cortex

22
Q

Info from the center (macula) of visual fields projects to which part of the striate cortex?

A

The occipital part of striate cortex

23
Q

Info from the lower half of visual cortex projects to which part of the striate cortex?

A

The upper bank of calcarine sulcus - ie striate cortex above the calcarine sulcus

24
Q

Fibres carrying info from the lower half of the visual field to the upper striate cortex project into which lobe?

A

Parietal lobe

25
Q

Fibres carrying info from the upper half of the visual field to the lower striate cortex project into which lobe?

A

Temporal lobe

26
Q

What is meant by scotoma?

A

Localised patch of blindness

27
Q

What is meant by anopia?

A

Loss of one or more quadrants of visual field

28
Q

What is meant by hemianopia?

A

Loss of half of visual field

29
Q

What is meant by quadrantanopia?

A

Loss of visual field in one quadrant

30
Q

What is meant by homonymous visual field loss?

A

Visual field losses are similar on both sides

31
Q

What is meant by heteronymous visual field loss?

A

Visual field losses are different on different sides

32
Q

Information from the upper peripheral temporal region of the right eye will project to which part of the striate cortex in which cerebral hemisphere and why?

A

Left cerebral hemisphere - temporal right = right half of vision
Rostral striate cortex = from periphery
Lower striate cortex, below calcarine sulcus = from upper half of visual field

33
Q

Complete loss of vision from one eye indicates a lesion at which part of the visual pathway?

A

In the optic nerve

34
Q

Loss of vision from part of both eyes suggests damage to the visual pathway way?

A

At the level of the optic chiasm or beyond

35
Q

What is the pupillary light reflex?

A

Ability of both pupils to respond (dilate or constrict) dependent on the level of light reaching the retina

36
Q

Which muscle is involved in constriction of the pupil, is it under sympathetic or parasympathetic control?

A

Sphincter pupillae - Parasymapthetic

37
Q

Which muscle is involved in dilation of the pupil is it under sympathetic or parasympathetic control?

A

Dilator pupillae - Sympathetic

38
Q

Which cranial nerves carry the afferent and efferent limbs of the pupillary light reflex?

A
Afferent = CN2 (optic)
Efferent = CN3 (occulomotor)
39
Q

What are the 2 components of the pupillary light reflex?

A

1) Direct component - light in one eye, the same pupil constricts
2) Consensual component - light in one eye, other pupil constricts

40
Q

What percentage of optic nerve fibres travel to the pre-tectal area?

A

10%

41
Q

What happens at the pre tectal area?

A

Some optic nerve fibres synapse with interneurones which have 2 axons which project to the edniger-westphal nucleus

42
Q

What happens at the edinger-westphal nucleus?

A

Interneurones synapse with preganglionic parasympathetic fibres carried in CN3

43
Q

Where do pre ganglionic and post ganglionic fibres to spinchter pupillae synapse?

A

In the ciliary ganglion

44
Q

Why does the consensual component of the pupillary light reflex exist?

A

Optic nerve from one side synapses with interneurones which give off axons to edniger westphal nuclei on both sides (thus synapsing with occulomotor neurones on both sides)

45
Q

If the optic nerve on one side was cut how would this affect both components of the pupillary light reflex, would the eye be permanently dilated?

A

Loss of direct reflex
Can still constrict due to consensual part of reflex when light is shone in other eye
Eye would not be permanently dilated due to influence of other eye

46
Q

If the occulomotor nerve on one side was cut, how would this affect both components of the pupillary light reflex, would the eye be permanently dilated?

A

Loss of direct reflex
Loss of consensual reflex when light shone in other eye
Consensual reflex when light is shone in that eye still present - ie causes other eye to constrict
Eye would be permanently dilated due to unopposed sympathetic action

47
Q

In which area of the brain stem is the somatic occulomotor nucleus, the edinger westphal nucleus and the pre-tectal area located?

A

The midbrain