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C&M Neuroanatomy > Week 11: Visual Pathway Lecture > Flashcards

Week 11: Visual Pathway Lecture Flashcards

1
Q

How does light information travel from the retina to the cortex?

A
  1. Light information reaches retina at back of eye
  2. From there, the optic nerve emerges and carries information to the optic chiasma
  3. The optic tract travels to the lateral geniculate nucleus in the thalamus
  4. Optic radiations bring information from the thalamus to the primary visual cortex in the occipital lobes
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2
Q

What is the order of layers of the front of the eye that light passes through?

A
  1. Cornea and sclera
  2. Choroid
  3. Pupil
  4. Lens
  5. Retina
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3
Q

What structures is the choroid continous with?

A

lens and ciliary muscle

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4
Q

What is found in the neural layer of the retina?

A
  • photoreceptors, bipolar cells, ganglion cells

- ganglion cell axons form the optic nerve

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5
Q

Where does the optic nerve exit the retina?

A

at the optic disc

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6
Q

What is another word for the optic disc?

A

blind spot –> any light information that falls in this region is invisible to us because there are no photoreceptors in this region

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7
Q

What does the non-neuronal layer of the retina consist of?

A
  • pigmented epithelium
  • pigmented epithelium contain melanin
  • sits against the choroid
  • is light absorbing
  • provides nutrients to photoreceptors
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8
Q

Explain how light information goes from the pigmented epithelium to the optic nerve ?

A
  • pigmented epithelium absorbs light and transmits information to rods and cones
  • horizontal interneuron
  • these photoreceptors pass information to bipolar cells (1st order)
  • amacrine interneuron
  • bipolar cells link to ganglion cells (2nd order)
  • these axons combine to form the optic nerve
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9
Q

What is the function of the horizontal and amacrine interneurones?

A

to modulate the transmission of information

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10
Q

Give 4 features of each:

  1. rods
  2. cones
A

Rods:

  • 20x more common
  • sensitive to light
  • vision in dim light
  • high level of convergence

Cones:

  • responsible for colour vision
  • high visual acuity
  • lower level of convergence
  • at the macula, one cone to one ganglion cell
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11
Q

Why does the optic nerve have meninges?

A

it is an outgrowth from the diencephalon so it is actually part of the CNS

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12
Q

What is papilloedema?

A
  • a swelling of the optic disc
  • increase in CSF pressure in head is transmitted to the layers surrounding the optic nerve
  • increases pressure and compresses the central retinal vein preventing venous drainage from the eye
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13
Q

What are the symptoms of papilloedema?

A
  • headaches
  • drowsiness
  • blurred vision
  • vomiting
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14
Q

Where is the primary visual cortex?

A

above and below the calcarine sulcus in the occipital lobe

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15
Q

Explain the 3 neuron visual pathway from photoreceptor to cortex

A
  1. Bipolar cells
  2. Ganglion cells
  3. Axons of ganglion cells run over retina to optic disc to form optic nerve
  4. Optic nerve projects to LGN
  5. Thalamocortical neurones (3rd order) travel in optic radiations to visual cortex
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16
Q

How is the visual pathway retinotopically organised?

A
  • left half of visual field goes to right hemisphere
  • right half of visual field goes to left hemisphere
  • upper visual field goes to lower bank of calcarine sulcus
  • lower visual field goes to upper bank of calcarine sulcus
  • macula goes to occipital pole
17
Q

How are images from the retina percieved?

A

mirror reversed and flipped upside down

18
Q

What is the fixation point?

A
  • when 4 quadrants transect and are divided by a horizontal line
  • corresponds to fovea
19
Q

Which fibres cross at the optic chiasma?

A

nasal fibres

20
Q

Which fibres do NOT cross at the optic chiasma?

A

temporal fibres –> they remain ipsilateral

21
Q

How do lower visual field fibres reach the upper bank of the calcarine sulcus?

A

through the superior trajectory

22
Q

How do upper visual field fibres reach the lower bank of the calcarine sulcus?

A

through the inferior trajectory (Meyer’s loop)

23
Q

Where are nasal and temporal fibres found?

A

nasal are more medial / further into the nose

temporal field is further into the periphery/ more lateral

24
Q

How is the primary visual cortex retinotopically organised?

A
  • the macula is represented most posteriorly (toward the tip of the occipital pole)
  • the peripheral fields are represented more anteriorly
25
Q

What do the following words mean:

  1. Scotoma
  2. Anopia
  3. Hemianopia
  4. Quadrantanopia
A
  1. localised patch of blindness
  2. refers to the loss of one or more quadrants of the visual field
  3. half of the visual field lost
  4. quarter of the visual field lost
26
Q

What does homonymous and heteronymous mean?

A

homonymous - visual field losses are similar for both sides

heteronymous - visual field losses are on different sides

27
Q

What is:

  1. Monocular blindness
  2. Bitemporal hemianopia
  3. Homonymous hemianopia
A
  1. Loss of both visual fields in one eye. Would be a lesion to the optic nerve
  2. Heteronymous hemianopia. Visual field losses of both temporal fields
  3. Loss of same visual field on both eyes
28
Q

Not all optic tract fibres go to the LGN. Approx 10/5 go where?

A

They take a medial root to the pre tectal area in the mid brain

29
Q

What is the pupillary light reflex?

A

the ability of BOTH pupils to respond (constrict or dilate) in response to light shone on the retina

30
Q

How does the pupillary light reflex work?

A
  1. Light is shone in a patients eye
  2. CN II (optic nerve) brings information to the pre-tectal area of the midbrain
  3. Interneurones link this information with the Edinger-Westphal nuclei of CN III
  4. CN III (oculomotor nerve) sends efferent parasympathetic fibres
  5. Pre-ganglionic fibres reach the ciliary ganglion
  6. Post-ganglionic fibres reach the sphincter pupillae
  7. Both eyes constrict
31
Q

In the pupillary light reflex, which is the direct response and which is the consensual response?

A

Direct: light in one eye, same pupil constricts
Consensual: light in one eye, other pupil constricts

32
Q

What will be the effect of a CN II lesion?

A

loss of a direct and consensual pupillary light reflex as information won’t reach the CNS

33
Q

What will be the effect of a CN III lesion?

A

loss of consensual pupillary light reflex

34
Q

What is the accomodation reflex?

A

a series of changes that occur when gaze is transferred from a distant to near object

35
Q

When you bring a pen from far to close to you, what 3 things should you expect to happen?

A
  1. Ciliary muscles contract so lens thickens
  2. Pupils constrict: due to the action of the sphincter pupillae
  3. Ocular convergence: contraction of the medial rectus so eyes converge medially to focus the gaze of the central object
36
Q

Explain the accommodation reflex

A
  • afferent fibres carry visual input to visual cortex: optic nerve and tract, LGN to visual cortex
  • fibres pass to CN III nuclei in midbrain (Edinger-westohal and motor nucleus)
  • parasympathetic to sphincter pupillae & ciliary muscles
  • motor to medial rectus

C&M Neuroanatomy (44 decks)

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