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Flashcards in Visual pathways Deck (19)
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1
Q

Which fibres under anatomical decussation & where?

A

Nasal retinal fibres.

At the optic chiasm.

2
Q

Explain the basic visual pathway after the optic chiasm?

A

Optic chiasm > LGN > optic radiations > primary visual cortex.

3
Q

What are the two divisions of the optic radiations known as?

A

Upper division = Baums loop.

Lower division = Meyers loop.

4
Q

What retinal quadrants input into the upper divisions of the optic radiation? What quadrants of the visual field are they from?

A

Superior retinal quadrants - inferior quadrants of the visual field.

5
Q

What retinal quadrants input into the lower divisions of the optic radiation? What quadrants of the visual field are they from?

A

Inferior retinal quadrants - superior quadrants of the visual field.

6
Q

What would a lesion to the upper divisions of the optic radiations cause?

A

Homonymous inferior quadrantanopia.

7
Q

What would a lesion to the lower divisions of the optic radiations cause?

A

Homonymous superior quadrantanopia.

8
Q

What are the two sets of muscles in the iris & what do they do?

A

Sphincter pupillae muscles - pupil constriction.

Dilator pupillae muscles - pupil dilation.

9
Q

Describe the pathway involved in the pupillary light reflex?

A

Light shone into eye > depolarisation of retinal ganglion cells > retinal gangion cell axons converge to form the optic nerve > optic nerve synapses with pretectal nucleus (on ipsilateral side) > pretectal nucleus axons synapse on the Edinger-Westphal nucleus on both sides of the brain > Axons from the Edinger-Westphal nucleus (occulomotor nevre) synapse on ciliary ganglion neurones > short ciliary nerves from the ciliary ganglion innervate the sphincter pupillae muscle > pupil constriction.

10
Q

What nerve is involved in the afferent limb of the pupillary light reflex?

A

Optic nerve.

11
Q

What nerve is involved in the efferent limb of the pupillary light reflex?

A

Occulomotor nerve.

12
Q

What is RAPD and what does it signify?

A

Relative afferent pupillary defect - lesion in the optic nerve anterior to the optic chiasm.

13
Q

What does RAPD allow a diagnosis of?

A

Retrobulbar neuritis.

14
Q

What three actions are involved in pupil accommodation?

A

Pupil constriction.
Lens accommodation.
Convergence.

15
Q

What is convergence and how does it occur?

A

Adduction of the eyes nasally.

It occurs due to excitation of the occulomotor nucleus > contraction of the medial rectus muscles.

16
Q

What is lens accommodation and what does it achieve?

A

Increased curvature of the lens > increased refractive power.

17
Q

Explain how lens accommodation occurs?

A

Contraction of the ciliary muscles (due to innervation by the short ciliary nerve) > decreased tension in the zonule of zinn > increased lens curvature.

18
Q

What is dorsal midbrain syndrome & what are its signs?

A

Lesion of the dorsal midbrain resulting in:
> Argyll Robertson pupil - bilateral small pupils that only constrict in response to accommodation & not light.
> Paralysis of upgaze.
> Convergence-retraction nystagmus - on attempting upgaze the eyes converge & retract.

19
Q

What are the causes of dorsal midbrain syndrome?

A

Pineal tumours.

Neurosyphilis.