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Phase 1b - Neurology & Neuroscience > Visual System - Pathways > Flashcards

Visual System - Pathways Flashcards

1
Q

What are the main visual pathway landmarks (7)?

A
  1. Eye
  2. Optic Nerve
  3. Optic Chiasm
  4. Optic Tract
  5. Lateral Geniculate Nucleus
  6. Optic Radiation
  7. Primary Visual Cortex or Striate Cortes
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2
Q

Which nerve connects the eye to the brain?

A

Optic nerve (CNII)

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3
Q

Where do the optic nerves from both eyes converge?

A

Optic chiasm

Anteriosuperiorly of the brainstem

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4
Q

What happens at the optic chiasm?

A
  • Approximately half of the ganglion nerve fibres (optic nerve) contralaterally exit along the optic tract
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5
Q

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

A

Lateral geniculate nucleus

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6
Q

What is the lateral geniculate nucleus and where is it?

A
  • It is a relay centre situated within the thalamus
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7
Q

What forms the fourth order neurones?

A

Optic radiation

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8
Q

What is the function of the 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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9
Q

Where is the primary visual cortex?

A

Within the occipital lobe

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10
Q

What is the striate cortex?

A

Primary visual cortex

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11
Q

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

A
  • The extra-striate cortex
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12
Q

What are the first order neurones within the visual pathway?

A

Rod & Cone photoreceptor cells

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13
Q

What are the second order neurones within the visual pathway?

A

Retinal bipolar cells

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14
Q

What are the third order neurones within the visual pathway?

A

Retinal ganglion cells (optic nerve)

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15
Q

Which fibres comprise the optic nerve?

A

Myelinated ganglion nerve fibres

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16
Q

Where are the cell bodies of the optic nerve located?

A

Within the retina

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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 to the optic chiasm will affect which visual fields?

A

Temporal Field Deficit in Both Eyes -> Bitemporal Hemianopia

Damages crossed ganglion fibres from nasal retina in both eyes

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20
Q

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

A
  • Both eyes:
    • Right sided lesion –> Left Homonymous Hemianopia in Both Eyes
    • Left sided lesion –> Right Homonymous Hemianopia in Both Eyes
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21
Q

Where do crossed fibres originate from?

A

Nasal retina

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22
Q

What is the function of crossed fibres?

A

Responsible for the temporal half of the visual field in each eye

23
Q

Where do uncrossed fibres originate?

A

Temporal retina

24
Q

What is the function of uncrossed fibres?

A

Responsible for nasal visual field

25
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
26
Q

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

A

Damage to the primary visual cortex (often caused by a stroke)

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

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
29
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
30
Q

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

A
  • Right homonymous hemianopia in both eyes
31
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

32
Q

What is the common cause of homonymous hemianopia?

A
  • Stroke (Cardiovascular Accident)
33
Q

Why is macula central vision spared in homonymous hemianopia?

A
  • Receives dual blood supply from both right and left posterior cerebral arteries
34
Q

What is the function of the pupil?

A

Regulates light input to the eye like a camera aperture

35
Q

When light intensities increase, what is the pupillary response?

A
  1. Constrictions to decrease spherical abberations and flare
  2. Increases depth of field (near response triad)
  3. Reduced bleaching of photopigments
36
Q

What is the resultant effect with increasing the depth of field?

A

The eye optical system is able to maintain a clear focus over a certain range of viewing distance even without relying on accommodation

37
Q

Which nerve mediates the pupillary dilatation?

A

Sympathetic oculomotor nerve

38
Q

When light intensities decrease, what is the pupillary response?

A
  1. Relaxation to increase spherical abberations and flare
  2. Decreases depth of field (near response triad)
  3. Increased bleaching of photopigments
39
Q

What is the effect on vision in eyes with shallow depth?

A

Focus is easily lost even with the slightest object movement

40
Q

Which cranial nerve mediates the pupillary constriction?

A

Parasympathetic oculomotor nerve (CNIII)

41
Q

Which muscles cause pupillary constriction?

A

Circular sphincter pupillae muscles

42
Q

Which muscles cause pupillary dilatation?

A
  • Radial dilator pupillae
43
Q

Outline the pupillary reflex (11).

A
  1. Light
  2. Rod and Cone photoreceptors
  3. Synapsing on Bipolar Cells
  4. Synapsing on Retinal Ganglion Cells (pupil-specific ganglion cells)
  5. PSGCs exit at posterior 3rd of optic tract
  6. Enter the Lateral Geniculate Nucleus
  7. Synapse on Edinger-Westphal Nuclei on both sides in the brainstem
  8. Oculomotor Nerve Efferent
  9. Synapses at Ciliary ganglion
  10. Short Posterior Ciliary Nerve
  11. Pupillary Sphincter
44
Q

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

A

Posterior 3rd of the optic tract

45
Q

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

A

Edinger-Westphal Nuclei

46
Q

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

A

Oculomotor nerve

47
Q

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

A

Ciliary ganglion

48
Q

Which nerve directly innervates the pupillary sphincter muscles?

A

Short posterior ciliary nerve

49
Q

What is a direct light reflex?

A
  • Constriction of the pupil of the light stimulated eye
50
Q

What is a consensual light reflex?

A

Constriction of pupil of the other eye

51
Q

Which clinical test can be conducted to test pupillary defects?

A
  • Swinging torch test
52
Q

What is the effect of right afferent pupillary pathway damage?

A
  • No pupil constriction in both eyes when right eye is stimulated with light
  • Normal pupil constriction in both eyes when left eye is stimulated with light
53
Q

What is the effect of right efferent pupillary pathway damage?

A
  • No right pupil constriction whether right or left eye is stimulated with light
  • Left pupil constricts whether right or left eye is stimulated with light

Phase 1b - Neurology & Neuroscience (18 decks)

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