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SF2 - Test 3 > 2 - Visual System Pathways > Flashcards

2 - Visual System Pathways Flashcards

1
Q

How does the lens alter images?

Rods?

Cones?

Fovea?

A

Reverses, Inverts

Rods - Low light, periphery

Cones - Color, center (fovea)

Fovea - Center of cone field; no blood vessels/interneurons, etc.–nothing in the way

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2
Q

Temporal vs Nasal Visual Field

Temporal vs Nasual Retinal Field

A
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3
Q

Retinal blood supply

A

Opthalmic Retinal Artery (CRA) - Penetrates meninges surrounding optic nerve and supplies inner retina

Ciliary Artery - Penetrates sclera near optic nerve exit and supplies the choriocapillaris

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4
Q

Overall Route of Phototransduction

A
  1. RPE - Retinal pigment epithelium - absorb/scatter light
  2. ONL - Outer Neuronal Layer - rods/cods
  3. OPL - Outer Plexiform Layer - horizontal/bipolar cells
  4. INL - Inner Nuclear Layer - bipolar
  5. IPL - Inner Plexiform Layer - bipolar/amacrine cells
  6. GCL - Ganglion Cell Layer - sends signals

**Don’t need to memorize layer names or oder; just rough concept of signal detection, modulation, and transmission**

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5
Q

What fibers is the orientation of data transfer to the optic nerve with respect to the visual field?

A

Only Nasal fibers cross optic chiasm (sees temporal part of visual field)

Temporal Fibers (sees nasal part of visual field) do NOT cross optic chiasm

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6
Q

Optic N. vs Optic Chiasm vs Optic Tract

A

Optic Nerve - Pre-Chiasm

Optic Chiasm - Cross over

Optic Tract - Post-Chiasm

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7
Q

Four Promary Targets for RGC fibers in brain?

A
  1. Lateral Geniculate Nucleus (LGN) (thalamus)
  2. Superior Colliculus (midbrain)
  3. Pretectum (midbrain)
  4. Hypothalamus
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8
Q

Geniculocalcarine vs Extrageniculate Tracts

A

Geniculocalcarine - Primary projection to LGN

Extrageniculate - Primary projection to Superior Colliculus

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9
Q

Outermost portion of the retina?

What lies beneath?

What synapses occur here?

A

Retinal Pigment Epithelium (RPE) - Melanin cointaining cuboidal cells

Outer Nuclear Layer (ONL) - Location of the photoreceptors

Synapses with Bipolar Cells, Horizontal Cells occur in the Outer Plexiform Layer (OPL)

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10
Q

Müller Glia (M) Cells

A

Processes spread the entire retina

Perform many functions, involved in synapse formation in the retina

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11
Q

Blood supply for Lateral Geniculate Nucleus (LGN)?

A

Anterior Choroidal Artery

Posterior Cerebral Artery (PCA)

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12
Q

Organization of LGN?

Role in binocular vision?

A

Layered structure with each layer receiving input from one eye

For binocular zone, all points in space of the retina of each eye are represented in their entirety via a series of vertical columns in the LGN

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13
Q

Parvocellular Layer of LGN

A

Color and Form Vision from Central Retina

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14
Q

Magnocellular Layers of LGN

A

Movement information of peripheral retina

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15
Q

How is information sent from the LGN to the Visual Cortex?

A

Geniculocalcarine Tract

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16
Q

Geniculocalcarine Tract

Function

Fibers + Travel Path

Blood Supply

A

Function: Connects LGN to Primary Visual Cortex

Fibers + Travel: Optic Radiations, travel through retrolenticular portion of posterior limb of the internal capsule

Blood Supply: Middle and Posterior Cerebral Arterys (MCA/PCA)

17
Q

Geniculocalcarine Tract

Major Divisions

A

2x

Upper Division: Projects from MEDIAL LGN, travels OVER lateral ventricle towards upper portion of Visual Cortex–Cuneus Gyrus

Lower Division: Projects from LATERAL LGN, trabels UNDER inferior horn of lateral ventricle (Meyer’s Loop) towards lower portion of Visual Cortex–Lingual Gyrus

18
Q

Geniculocalcarine Tract

Contralateral Hemifield of Vision

A

Upper and Lower Optic Radiations in each hemisphers; represents half visual field

***Upper Division = LOWER half of visual field

Lower Division = UPPER half of visual field***

19
Q

Extrastriate Visual Pathways

Major Divisions

Common Target

A

Dorsal Extrastriate Projections: Connect V1/BA17 to Pareito-occipital association cortex (V5) - encode Motion and Spatial Relationships

Ventral Extrastriate Projections: Connect V1/BA17 to Occipitotemporal Association Cortex - encode Form (V3) and Color (V4)

- - -

In BOTH stream, connections to V2 (Prestriate Cortex/Secondary Visual Cortex) - provide further redinement of properties encodes by V1

20
Q

Superior Colliculus

Function

Type of Information

Connection to LGN

A

Tectal Structure

Function: Secondary Pathway that supplements Geniculocalcarine Tract; may compensate for lesions

Information: Moving stimuli, regulates Saccades (high velocity eye movements); important for “refreshing” eye gaze

Connection: Brachium connects to LGN

21
Q

Superior Colliculus:

Targets

A

1. Cranial Nerves III and IV: Regulate horizontal eye movement

  1. Upper Spinal Cord - via tectospinal tract; reflexive movement toward visual input
  2. Pons/Cerebellum - Coordinate eye/head movement; quick adaptation, balance, posture
  3. Pulvinar - Medially located thalamic nucleus
22
Q

Pulvinar pathway / function

A

Function: Projects to extra striate visual areas, assimilate different modalities to create construct of objects in visual space

Pathway: Retina - Superior Colliculus - Pulvinar - Extrastriate Cortex

**Works in parallel with geniculocalcarine tract**

23
Q

Pretectum and Hypothalamus

A

RGCs project here (in addition to LGN/Superior Colliculus) to regulate eye response to changes in ambient light

24
Q

Pretectum:

Function

Target

Regulates

Clinical Use

A

Function: ACUTE changes to ambiet light

Target: Edinger-Westphal Nucleus; parasympathetic fibers project to the eye to regulate pupil constriction, lens accommodation, and eye convergence

Regulates: Pupillary Light Reflex through Edinger-Westphal Nucleus

Clinical: Test CN II and III

25
Q

Hypothalamus (and vision)

Function

Clinical Relevance

A

Function: Suprachiasmatic Nucleus (SCN) located here; receives input from primitive light-sensitive RGCs that respond to ambient light

Clinical Relevance: Links Circadian rhythem and hormonal cycles with levels of ambient light

26
Q

Progressive Encephalization

A

Mammals have increased cortical processing of visual stimuli

27
Q

Clinical: Cortical Blindness

How can “blindsight” occur?

A

Lesion of BA 17 / V1

Loss of conscious visual perception

Can still respond to stimuli w/out conscious perception

“Blindsight” is thought to occur via the Extrageniculate Pathway (retina-superior colliculus-pulvinar-extrastriate cortex)

28
Q

Clinical: Anton’s Syndrome

A

Visual Anosognosia

Denial of losing vision

29
Q

Clinical: Visual Hallucinations cause?

A

Seizures in the inferior occipitotemporal cortex

30
Q

Clinical: Prosopagnosia

A

Face blindness

right or bilateral fusiform gyrus lesion

“man who thought his wife was a hat”

31
Q

Clinical: Achromatopsia

A

Disorder of color perception

Color perception occurs, but fails at identification stage; caused by fusiform gyris lesion

32
Q

Clinical: Metamorphopsia

A

Distorion of size and shape (“Alice in Wonderland” syndrome)

Lesions in Inferior or Lateral Visual Association Cortex

33
Q

Clinical: Balint’s Syndrome

A

Caused by bilateral lesions of Dosolateral parieto-occipital cortex (“where” stream)

Symptoms:

  1. Simultanagnosia (random shifting of visual field perception)
  2. Optic Ataxia (lack of hand eye coordination)
  3. Ocular Apraxia (impaired gaze direction/saccades)
34
Q
A

SF2 - Test 3 (25 decks)

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