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Anatomy & Physiology 2 > Visual Pathways > Flashcards

Visual Pathways Flashcards

1
Q

What is the retrochiasmal pathway?

A

The retrochiasmal pathway begins posterior to the optic chiasm with the optic tracts then travels to the lateral geniculate nuclei, the temporal lobe optic radiations (i.e., Meyer’s loop), the parietal lobe optic radiations, and ends in the occipital cortex.

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2
Q

What do chiasmal lesions result in?

A

Bitemporal hemianopia (common in pituitary adenoma)

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3
Q

What do retrochiasmal lesions result in?

A

Contralateral homonymous field defect

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4
Q

Why do V1 lesions often result in homonymous hemianopia with macular sparing?

A

Due to dual blood supply of the occipital lobe where the macula is represented

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5
Q

What are the layers of the retina?

A

LIGHT COMES IN:

Inner limiting membrane
Optic Nerve Fibres
Ganglion Cells
Inner Plexiform Layer
(Amacrine)
Inner Nuclear Layer
(Bipolar)
Outer Plexiform Layer
(Horizontal)
Outer Nuclear Layer
(Photoreceptors)
Outer Limiting Membrane
Rods & Cones
Retinal Pigment Epithelium
Brunch’s Membrane

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6
Q

How is light transduced into electrical impulses?

A

Photoreceptors (rods & cones)

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7
Q

Once light is transduced into electrical impulses, what cells and axons do they go to?

A

Retinal ganglion cells and the axons of these form the optic nerve

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8
Q

What are the two types of retinal ganglion cells?

A

Parasol & Midget

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9
Q

In an OCT, what is the innermost layer (top layer)?

A

Nerve Layer

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10
Q

How is the optic nerve formed?

A

Axons of retinal ganglion cells (parasol and midget) around 1.2 million

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11
Q

What are the 4 main parts of the optic nerve and how long are they?

A

Intraocular - 1mm
Intraorbital - 25-30mm
Intracanalicular - 4-10mm
Intracranial - approx. 10mm

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12
Q

Where is the LGN?

A

Layered structure that’s located posterolaterally to the dorsal thalamus

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13
Q

What root of the optic tract does the LGN receive information from?

A

The large lateral root & receives fibres from both eyes (as after the optic chiasm)

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14
Q

How many layers of the LGN are there?

A

6

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15
Q

Which layers of the LGN are ipsilateral?

A

2, 3, 5

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16
Q

Which layers of the LGN are contralateral?

A

1, 4, 6

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17
Q

What are the 2 distinct visual pathways to V1?

A

Magnocellular (M) pathway
Parvocellular (P) pathway

They remain separated from the retina up to V1 (fibres don’t mix as they travel along the visual pathway)

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18
Q

What is the third pathway to V1 that we don’t need to know well?

A

Koniocellular pathway whose function is less well-defined

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19
Q

Which layers of the LGN do the magnocellular pathway cells go to?

A

Layers 1 - 2

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20
Q

Which layers of the LGN do the parvocellular pathway cells go to?

A

Layers 3 - 6

21
Q

Where do the M & P cells lie?

A

In grey matter layers

22
Q

Where do M & P cells terminate in V1?

A

Layer IV (4) of V1

23
Q

Where do koniocellular layers lay?

A

Between each layer within white matter

24
Q

Where are cell bodies of the nuclei?

A

In the grey matter.
Top part of cortex is where the grey matter is that’s 7 cells thick (where the cell body is) and then white matter neurons are in the lobes as this is where axons extend down. There’s also grey matter in the thalamus.

25
Q

Where are axons of the LGN?

A

In the white matter (myelinated)

26
Q

Are magnocellular cells small or large?

A

Magno = large

27
Q

What retinal ganglion cells feed into magnocellular cells?

A

Rapidly relay information to V1 from parasol retinal ganglion cells

28
Q

What are the magnocellular cells involved in?

A

Motion detection
Depth perception
Low acuity/resolution
High contrast sensitivity (monochromatic)

= Crude information

Rapid, saccadic eye movements rely on M-cell information.

M cells are vital for binocular vision & rapid eye-motor coordination for the body

29
Q

Where are magnocellular cells?

A

In the thalamus in Layers 1 and 2

30
Q

What are Parasol Retinal Ganglion cells?

A

They’re large and synapse with M cells. Have large, complex dendritic networks.
Heavy myelinated fibres for fast conduction

31
Q

What percentage of retinal ganglion cells are Parasol cells?

A

10% in one eye

32
Q

How many photoreceptors synapse with 1 parasol cell? & are they from rods or cones?

A

Multiple, mainly rods but with some cone input but no colour information

33
Q

What are parvocellular cells?

A

Small cells that slowly relay information to V1

34
Q

What cells feed into parvocellular cells?

A

Slowly relay information to V1 from Midget retinal ganglion cells

35
Q

What are parvocellular cells involved in?

A

High acuity/resolution of vision

Colour (chromatic processing)

Low contrast sensitivity

36
Q

What are Midget retinal ganglion cells?

A

Small RGC’s of 90% of a small, simple dendritic network
They’re less myelinated so are slower conduction

37
Q

What cells do Midget RGC’s synapse with?

A

P cells (Parvocellular)

38
Q

How many photoreceptors feed into Midget RGC’s?

A

1 Photoreceptor

39
Q

What % of nerve fibres do magnocellular and parvocellular cells made up?

A

10% - Magno
80% - Parvo

40
Q

Which cells are dominant in the retinotectal pathway?

A

Magnocellular

41
Q

What cells are dominant in the retinocalcarine pathway?

A

Parvocellular

42
Q

What is the Retinotectal Pathway?

A

Refer to fibres that travel from retina to pretectal nucleus (light reflex). Magnocellular fibres travel along this pathway to the pretectal nucleus and superior colliculus.

43
Q

What is the superior colliculus for? What cells travel here?

A

Rapid motor reflexes involving cranial nerves and spinal motor neuronal pathways
Magno cellular

44
Q

What is the Retinocalcarine pathway?

A

Parvocellular fibres travel via the LGN to the calcarine sulcus, where V1 lies

45
Q

What is V1 also known as?

A

Brodmann’s Area 17

46
Q

What are the secondary and tertiary visual cortexes also known as? & what are they for?

A

V2
V3 & V5

Higher order visual processing

47
Q

What layer in the visual cortex does the majority of input from the LGN go to?

A

Layer IVC (Layer 4C)

Other layers send fibres to extrastriate areas, i.e. areas of visual cortex that do not receive strong direct input from LGN. This is mostly concerned with subconscious visual processing.

48
Q

What is Retinotopic mapping?

A

The order of retinal neurons is maintained throughout the visual pathway (except at higher cortical areas) so neighbouring regions of the image are represented by neighbouring regions of the visual area

Anatomy & Physiology 2 (12 decks)

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