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Z YEAR 2 BRS NEURO > Visual Pathway > Flashcards

Visual Pathway Flashcards

1
Q

What does the visual pathway transmit?

A

signal from eye to the visual cortex

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2
Q

What is the optic nerve?

A
  • Ganglion Nerve Fibres

- Cell bodies originating in retina

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3
Q

What is the optic chiasm?

A

Half of the nerve fibres cross here

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4
Q

What is the optic tract?

A

Ganglion nerve fibres exit as optic tract

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5
Q

What is the Lateral Geniculate Nucleus?

A

Ganglion nerve fibres synapse at Lateral Geniculate Nucleus (relay centre in thalamus)

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6
Q

What is optic radiation?

A

form fourth 4th order neuron relaying signal from the Lateral Geniculate Ganglion,
to the Primary Visual Cortex within the occipital lobe,
for lower visual processing

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7
Q

What does the primary visual cortex do?

A

relays visual information to the Extra-striate Cortex,
a region adjacent to the Primary Visual Cortex,
for further higher visual processing

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8
Q

What are first order neurons?

A

Rod and Cone Retinal Photoreceptors

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9
Q

What are second order neurons?

A

Retinal Bipolar Cells

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10
Q

What are third order neurons?

A

Retinal Ganglion Cells

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11
Q

What is the process of the visual pathway from retinal ganglion cells?

A
  1. Optic Nerve (CN II)
  2. Partial Decussation at Optic Chiasma – 53% of ganglion fibres cross the midline
  3. Optic Tract
  4. Lateral Geniculate Nucleus (LGN) in Thalamus – to relay visual information to Visual Cortex
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12
Q

How is signal tramission improved?

A

retinal ganglion fibres become myelinated after entering the optic nerve

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13
Q

Where to retinal ganglion fibres terminate?

A

at the Lateral Geniculate Ganglion,

and synapse upon the fourth order neurons, or Optic Radiation

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14
Q

What do lesions anterior to optic chasm affect?

A

visual field in one eye only

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15
Q

What do lesions posterior to optic chasm affect?

A

affect visual field in both eyes

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16
Q

What percentage of ganglion fibres cross at optic chiasma?

A

53%

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17
Q

Where do the crossed fibres originate and what are they responsible for?

A

originating from nasal retina, responsible for temporal visual field

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18
Q

Where do the crossed fibres originate and what are they responsible for?

A

originating from temporal retina, responsible for nasal visual field

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19
Q

What does a lesion at the optic chiasm cause?

A

•Damages crossed ganglion fibres from nasal retina in both eyes
•Temporal Field Deficit in Both Eyes e.g. Bitemporal
Hemianopia

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20
Q

What does a right sided posterior lesion posterior to optic chiasm cause?

A

Left Homonymous Hemianopia in Both Eyes

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21
Q

What does a left sided posterior lesion posterior to optic chiasm cause?

A

Right Homonymous Hemianopia in Both Eyes

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22
Q

What is bitemporal hemianopia caused by usually?

A
  • Typically caused by enlargement of Pituitary Gland Tumour

* Pituitary Gland sits under Optic Chiasma

23
Q

What is a homonymous hemianopia caused by?

A

Stroke (Cerebrovascular Accident)

24
Q

What is a homonymous hemianopia with macular sparing?

A

-usually with damage to Primary Visual Cortex
- area within the Primary Visual Cortex representing the macula is well protected,
as it receives dual blood supply from both right and left posterior cerebral arteries
-If damage on occipitcal cortex, macular sparing, information to brain from macula spread on widest part on occipital cortex and most likely good part of it will be spared

25
Q

When does homonymous hemianopia with macular sparing happen?

A
  • Often due to stroke

* Leads to Contralateral Homonymous Hemianopia with Macula Sparing

26
Q

What happens to the macula in homonymous hemianopia with macular sparing?

A

receives dual blood supply from Posterior Cerebral Arteries from both sides

27
Q

What happens to the pupil in light?

A

constrict

28
Q

How and why does the pupil constrict in light?

A
  1. decreases spherical aberrations and glare
  2. increases depth of field – see Near Response Triad from Previous Lecture
  3. reduces bleaching of photo-pigments
  4. Pupillary constriction mediated by parasymapthetic nerve (within CN III)
29
Q

What does the pupil do in dark?

A

dilate

30
Q

How and why does the pupil dilate in the dark?

A
  • increases light sensitivity in the dark by allowing more light into the eye
  • pupillary dilatation mediated by sympathetic nerve
31
Q

What does parasympathetic stimulation cause?

A

Circular muscles to contract (pupillary constriction)

32
Q

What does sympathetic stimulation cause?

A

Radial muscle contract (pupillary dilation)

33
Q

How is pupillary constriction mediated?

A

parasymapthetic nerve (within CN III)

34
Q

What is the afferent pathway pupillary reflex?

A

Red and green

  1. Rod and Cone Photoreceptors synapse on Bipolar Cells and synapse Retinal Ganglion Cells
  2. Pupil-specific ganglion cells exit at posterior third of optic tract
  3. Then enter Lateral Geniculate Nucleus and sunpse upon dorsal brain stem
  4. Afferent (incoming) pathway from each eye synapses on Edinger-Westphal Nuclei on both sides in the brainstem
35
Q

What is the efferent pathway pupillary reflex?

A

-Blue
1. Edinger-Westphal Nucleus to Oculomotor Nerve Efferent ->
2. Synapses at Ciliary ganglion then to Short Posterior Ciliary Nerve
3. Fibres go to Pupillary Sphincter
4. provided by the parasympathetic nerve arising from the brainstem,
synapsing at the Ciliary Ganglion upon the Short Posterior Ciliary Nerve

36
Q

What does the short posterior ciliary nerve innervate?

A

directly on the iris Pupillary Sphincter

37
Q

What does the afferent pathway from either eye stimulate? What does this mean?

A

-the efferent pathway on both eyes
-only one eye needs to be stimulated with light,
to elicit pupillary constriction response in both eyes

38
Q

What is direct light reflex?

A

Constriction of Pupil of the light-stimulated eye

39
Q

What is consensual light reflex?

A

Constriction of Pupil of the other (fellow) eye

40
Q

What is an example of a right afferent defect?

A

damage to optic nerve

41
Q

What would happen in a right afferent defect?

A
  1. No pupil constriction in both eyes when right eye is stimulated with light
  2. Normal pupil constriction in both eyes when left eye is stimulated with light
42
Q

What is an example of right efferent defect (pupil constriction)?

A

Damage to Right 3rd Nerve

43
Q

What happens in a right efferent defect?

A
  1. No right pupil constriction whether right or left eye is stimulated with light
  2. Left pupil constricts whether right or left eye is stimulated with light
    - there is an afferent signal but no efferent signal to that specific eye
44
Q

What happens in a unilateral afferent defect?

A

Difference response pending on which eye is stimulated

45
Q

What happens in unilateral efferent defect?

A

Same unequal response between left and right eye irrespective which eye is stimulated

46
Q

What happens in a relative afferent pupillary defect? What is the result in a swinging torch test?

A
  1. Partial pupillary response still present when the damaged eye is stimulated
  2. Elicited by the swinging torch test – alternating stimulation of right and left eye with light
  3. Both Pupils constrict when light swings to left undamaged side
  4. Both Pupils paradoxically dilate when light swings to the right damaged side
47
Q

When will both pupils constrict in a relative afferent pupillary defect in a swinging torch test?

A

when light swings to the left eye with intact afferent pathway (undamaged)

48
Q

When will both pupils paradoxically dilate in a relative afferent pupillary defect in a swinging torch test?

A

when the light swings to the right eye with damaged afferent pathway,
as a result of relatively reduced drive for pupillary constriction in both eyes

49
Q

What is the aim of swinging torch test?

A

timulate one eye at a time,

alternating between the right and the left ey

50
Q

What is vertical visual field loss most likely related to?

A

Neurological conditions

51
Q

What is horizontal visual field loss most likely related to?

A

eye condition e.g glaucoma

52
Q

What does the afferent pathway on either side alone simulate?

A

efferent (outgoing) pathway on both sides

53
Q

What happens if you shine a light in right eye?

A

Left eye pupil will contract as well

Z YEAR 2 BRS NEURO (21 decks)

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