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

Visual System - Pathways Flashcards

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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?

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A

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

23
Q

Where do uncrossed fibres originate?

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A

Temporal retina

24
Q

What is the function of uncrossed fibres?

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A

Responsible for nasal visual field

25
What is the common cause of bitemporal hemianopia?
* **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
Which structure is affected in patients with homonymous hemianopia with macular sparing?
Damage to the **primary visual cortex** (often caused by a stroke)
27
What is monocular blindness?
* **Loss of vision in a single eye**, due to damage to retinal ganglion nerve fibres anterior to the optic chiasm
28
Which type of visual field deficit arises from a lesion to the optic chiasm?
* Temporal field deficit in both eyes, considered to be **bitemporal hemianopia**
29
What type of visual field deficit arises from a right-side posterior to the optic chiasm lesion (optic tract, radiation or visual cortex)?
* Left homonymous hemianopia in both eyes
30
What type of visual field deficit arises from a left-side posterior to the optic chiasm lesion (optic tract, radiation or visual cortex)?
* Right homonymous hemianopia in both eyes
31
What happens to the retinal ganglion cell fibres at the optic chiasm?
Partial decussation at optic chiasm | 53% of ganglion fibres cross the midline into contralateral optic tracts
32
What is the common cause of homonymous hemianopia?
* Stroke (Cardiovascular Accident)
33
Why is macula central vision spared in homonymous hemianopia?
* Receives **dual blood supply** from both right and left posterior cerebral arteries
34
What is the function of the pupil?
Regulates light input to the eye like a camera aperture
35
When light intensities increase, what is the pupillary response?
1. Constrictions to decrease spherical abberations and flare 2. Increases depth of field (near response triad) 3. Reduced bleaching of photopigments
36
What is the resultant effect with increasing the depth of field?
The **eye optical system** is able to **maintain a clear focus** over a **certain range of viewing distance** even without relying on accommodation
37
Which nerve mediates the pupillary dilatation?
Sympathetic oculomotor nerve
38
When light intensities decrease, what is the pupillary response?
1. Relaxation to increase spherical abberations and flare 2. Decreases depth of field (near response triad) 3. Increased bleaching of photopigments
39
What is the effect on vision in eyes with shallow depth?
Focus is easily lost even with the slightest object movement
40
Which cranial nerve mediates the pupillary constriction?
Parasympathetic oculomotor nerve (CNIII)
41
Which muscles cause pupillary constriction?
Circular sphincter pupillae muscles
42
Which muscles cause pupillary dilatation?
* Radial dilator pupillae
43
Outline the pupillary reflex (11).
1. Light 1. Rod and Cone **photoreceptors** 1. Synapsing on **Bipolar Cells** 1. Synapsing on **Retinal Ganglion Cells** (pupil-specific ganglion cells) 1. PSGCs exit at posterior **3rd of optic tract** 1. Enter the **Lateral Geniculate Nucleus** 1. Synapse on **Edinger-Westphal Nuclei** on both sides in the brainstem 1. **Oculomotor Nerve Efferent** 1. Synapses at **Ciliary ganglion** 1. Short Posterior **Ciliary Nerve** 1. **Pupillary Sphincter**
44
Where do the pupil-specific ganglion cells exit out of the optic tract?
Posterior 3rd of the optic tract
45
Where do afferent pathways from each eye synapse within the brainstem?
Edinger-Westphal Nuclei
46
Which cranial nerve synapses with the Edinger-Westhphal nuclei in the efferent pathway?
Oculomotor nerve
47
Where does the oculomotor nerve synapse within the efferent pathway during the pupillary reflex?
Ciliary ganglion
48
Which nerve directly innervates the pupillary sphincter muscles?
Short posterior ciliary nerve
49
What is a direct light reflex?
* Constriction of the pupil of the light stimulated eye
50
What is a consensual light reflex?
Constriction of pupil of the other eye
51
Which clinical test can be conducted to test pupillary defects?
* Swinging torch test
52
What is the effect of right afferent pupillary pathway damage?
* **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
What is the effect of right efferent pupillary pathway damage?
* **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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