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BRS 2 > Visual System (Pathways) > Flashcards

Visual System (Pathways) Flashcards

1
Q

Which nerve connects the eye brain?

A

Optic nerve (II)

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2
Q

Which fibres comprise the optic nerve?

A

Myelinated ganglion nerve fibres

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3
Q

Where are the cell bodies of the optic nerve located?

A

The cell bodies reside within the retina

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4
Q

Where do the optic nerves from both eyes converge?

A

At the optic chiasm, anterio-superior of the brainstem

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5
Q

What happens at the optic chiasm?

A

Approximately half of the ganglion nerve fibres contralaterally exit along the optic tract.

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6
Q

Where do ganglion nerve fibres synapse with the next order neurones?

A

At the Lateral geniculate nucleus

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7
Q

Where is the lateral geniculate nucleus?

A

It is a relay centre situated within the thalamus

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8
Q

What forms the fourth order neurones?

A

Optic radiation

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9
Q

What is optic radiation?

A

Relays signals from the lateral geniculate ganglion to the primary visual cortex within the occipital lobe for lower visual processing

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10
Q

Where is the primary visual cortex?

A

Within the occipital lobe

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11
Q

What is the striate cortex?

A

Primary visual cortex

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12
Q

Which region is responsible for further high visual processing besides the primary visual cortex?

A

The extra-striate cortex.

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13
Q

What are the first order neurones within the visual pathway?

A

The Rod and Cone photoreceptor cells

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14
Q

What are the second order neurones within the visual pathway?

A

The retinal bipolar cells.

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15
Q

What are the third order neurones within the visual pathway?

A

Retinal ganglion cells

Optic nerve

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16
Q

What happens to the retinal ganglion cell fibres at the optic chiasm?

A

Partial decussation at optic chiasm- 53% of ganglion fibres cross the midline into contralateral optic tracts.

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17
Q

Where do retinal ganglion fibres terminate?

A

Within the lateral geniculate ganglion

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18
Q

A lesion occurring anterior to the optic chiasm will affect which visual fields?

A

Affect visual field in one eye only

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19
Q

A lesion occuring posterior to the optic chiasm will affect the visual field in which eyes?

A

Both eyes

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20
Q

Where do contralateral optic fibres originate from?

A

From nasal retina, responsible for the temporal half of the visual field in each eye

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21
Q

Where do the uncontrolled fibres predominantly originate from?

A

Originate from the temporal retina

22
Q

What are temporal retinal fibres responsible for?

A

Responsible for nasal half of the visual field in each eye.

23
Q

A lesion to the optic chiasm will result in damage to white fibres?

A

Predominantly damaging decussation contralateral retinal ganglion fibres

24
Q

Which type of visual field deficit arises from a lesion to the optic chiasm?

A

Temporal field deficit in both eyes, considered to be bitemporal hemianopia.

25
Q

What type of visual field deficit arises from a right-side posterior to the optic chiasm lesion (optic tract, radiation or visual cortex)?

A

Left homonymous hemianopia in both eyes.

26
Q

What visual field defect occurs in a left sided lesion to the posterior optic chiasm?

A

Right homonymous hemianopia in both eyes.

27
Q

What is monocular blindness?

A

Loss of vision in a single eye due to damage to retinal ganglion nerve fibres anterior to the optic chiasm.

28
Q

What is the common cause of bitemporal hemianopia?

A

Enlargement of the pituitary gland (adenoma)
Considering the pituitary gland resides within the sella turcica, beneath the optic chiasm –> Adenoma causes optic nerve compression

29
Q

What is the common of homonymous hemianopia?

A

Stroke (CVA)

30
Q

Which structure is affected in patients with homonymous hemianopia with macular sparing?

A

Damage to the primary visual cortex, caused due to a stroke.

–> This contralateral homonymous hemianopia

31
Q

Why is macula central vision spared in homonymous hemianopia?

A

Receives dual blood supply from both right and left posterior cerebral arteries.

32
Q

What is the function of the pupil?

A

Regulates light input to the eye like a camera aperture.

33
Q

When light intensities increase, wha tis the pupillary response?

A

Constrictions to decrease spherical abberations and flare

Increases depth of field – near response triad.

Reduced bleaching of photopigments

Mediated by oculomotor nerve

34
Q

Which cranial nerve mediates the pupillary constriction?

A

Parasympathetic oculomotor nerve (CNIII).

35
Q

When light intensities decrease, what is the pupillary response?

A

Increases light sensitivity in the dark my allowing more light into the eye, facilitated by pupillary dilatation.

36
Q

Which nerve mediates the pupillary dilatation?

A

Sympathetic oculomotor nerve

37
Q

Which muscles cause pupillary constriction?

A

Circular sphincter pupillae muscles

38
Q

Which muscles cause pupillary dilatation?

A

Radial dilator pupillae

39
Q

Where do the pupil-specific ganglion cells exit out of the optic tract?

A

The posterior third of the optic tract before entering the lateral geniculate nucleus

40
Q

Where do afferent pathways from each eye synapse within the brainstem?

A

Synapses on the Edinger-Westphal Nuclei on both sides of the brainstem

41
Q

Which brainstem nucleus is involved within the pupillary reflex?

A

Edinger-Westphal nuclei

42
Q

Which cranial nerve synapses with the Edinger-Westhphal nuclei in the efferent pathway?

A

Oculomotor nerve

43
Q

Where does the oculomotor nerve synapse within the efferent pathway during the pupillary reflex?

A

Ciliary ganglion

44
Q

Which nerve directly innervates the pupillary sphincter muscles?

A

The short posterior ciliary nerve

45
Q

What is a direct light reflex?

A

Constriction of the pupil of the light stimulated eye

46
Q

What is a consensual light reflex?

A

Constriction of pupil of the other eye

47
Q

What is the effect of right afferent pupillary pathway damage? (Damage to the right optic nerve)

A

Stimulation of the right eye will elicit weak

No pupillary constriction in both eyes.

However stimulation of the left eye will elicit normal pupillary responses in both eyes.

48
Q

What is the effect is the right efferent pathway is damaged?

A

There will be no pupil constriction in the right eye, irrespective of stimulation

49
Q

What is a unilateral afferent defect?

A

Difference responses pending on which eye is stimulated

50
Q

What is a unilateral efferent defect?

A

Produces the same unequal responses between left and right eye, regardless whether which eye is stimulated.

51
Q

Which clinical test can be conducted to test pupillary defects?

A

Swinging torch test

52
Q

What is the relative afferent pupillary defect?

A

Partial pupillary response still present when the damaged eye is stimulated
Elicited by the swinging torch test – alternating stimulation of right and left eye with light
Both Pupils constrict when light swings to left undamaged side
Both Pupils paradoxically dilate when light swings to the right damaged side

BRS 2 (62 decks)

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