White matter tracts Flashcards by J Abow

What are the 3 catergories that the white matter tracts are subdivided into?

Projection pathways
Association pathways
Commissural pathways

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What are the projection pathways?

Everything that connects from cortex to outside the brain

Fibres connecting cortex with subcortical centres

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What is the definition of pyramidal tract within projection pathway?

Longitudinal fibres from cortex through the pyramid

Only 3-4% from pyramidal cells of Betz

Only 50% to spinal cord (CST)

Many axons terminate in, or send collateral to stratium, thalamus, brainstem nuclei

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What does the projection pathway consist of?

Both afferent and efferent nerve fibres that couples brain with spinal cord

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What is the origin of Corticospinal/-bulbar tract?

Frontal lobe - M1 (BA4) 60%
Pre-motor and SMA (BA6)
Parietal lobe PCG 30%

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Where is premotor located?

Anterior to precentral gyrus

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Where is Suplementary motor area (SMA) located?

Midline surface of hemisphere anterior to primary motor cortex

Contributes to control of movement

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What is the cortico-motoneuronal (CM) system

Component of CST

Direct monosynaptic CM connections to motoneurons of many muscles

CM projections particularly strong to most distal musculature (face-hand-feet)

Only present in primates

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What is present only in primates?

Direct, cortico-motoneuronal projections

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What is not present in all primates?

CM connections

Best developed in most dexterous primates

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What are association pathways?

Connection within one hemisphere
Fibre pathways that lie within cerebrum that connect one part of cerebral cortex with another within same hemisphere
Long and short fibres interconnecting cortical areas of same hemisphere

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What is Neuronavigating system?

Makes a relationship between image and what it is observed in surgery

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What are the major tracts of association pathways?

Superior longitudinal fascicle (I-III)
Arcuate fascicle
Uncinate fascicle
Inferior longitudinal fascicle
Inferior fronto-occipital fascicle
Frontal Aslant tract

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What are involved in speech production and speech understanding/comprehension?

Multiple areas

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What is dual stream model?

Two functionally distinct/neural network that process speech/language information

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What does the dual stream model interface?

Sensory/phonological network with:

conceptual-semantic system
motor- articulatory system

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What does ventral of dual stream model deal with?

Comprehension = understanding

Mapping sound-to-meaning

Bilateral location in temporal lobe

Time invariant

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What does dorsal of dual stream model deal with?

Sensory-motor integration

Sound to motor mapping

Left dominance

Time variant

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What are the language concepts?

Broca-Wernicke- HG

Dorsal Stream - Arcuate fascicle

Ventral stream - Uncinate fascicle and Inferior longitudinal fascicle

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What is the Arcuate Fascicle?

Subdivision of the Superior longitudinal Fascicle

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What is the function of Arcuate Fascicle?

Connects Broca (or PrCG) to Wernicke

Where is Arcuate Fascicle located?

Around Sylvian Fissure

Deep to Insula and Parietal Lobe

What is the feature of AF?

Dorsal pathway Direct + Indirect

2. Phonolgy

What are the 3 segments that Catani showed?

Long segment coming from Broca going down to Temporal Lobe
Short segment connecting region of Broca with an area in Parietal Lobe
Another connecting parietal lobe to temporal lobe

What is anterior segment of SLF connected to?

1. Precentral Gyrus | 2. Supramarginal Gyrus

What is the posterior segment of SLF connected to?

1. Middle Temporal Gyrus | 2. Angular Gyrus

Arcuate Fascicle

Left lateralised in 95% R handed Connects PrCG (or Broca IFG) with Post temp Lesions Conductive aphasia

What is left lateral good for?

Better verbal intelligence Phonological processing

What are Broca's connections

1. U fibres - premotor/motor 2. Ascending fibres - dorsal premotor cortex 3. Caudo-posterior - supramarginal gyrus

What is Frontal Aslant Tract?

Connect superior and Inferior frontal gyri Pars opercularis - IFG - Broca Goes up to Anterior Cingulate and medial SFG - pre SMA

What is the deficit of Frontal Aslant Tract?

Verbal Fluency

What faciliates speech initiation?

pre SMA

What is Inferior Longitudinal Fascicle?

1. Occipital - Anterior Temporal Lobe 2. Part of ventral semantic stream/language comprehension 3. Deficits: Object recognition Face processing Visual semantic memory

What is Uncinate Fascicle?

``` Ant TL – Po-IFG & Fronto-orbital TL – Sylvian fissure – Inf PL – FL Indirect semantic pathway (+ ILF) Auditory working memory Deficits Single word comprehension & Naming ```

What are examples of Optic Radiation?

1. Inferior Longitudinal Fascicle 2. Splenium fibre 3. Optic Radiation 4. Optic Tract

What are Comissural pathways?

Connects cortex between hemispheres

What are the main types of commissural pathways?

1. Corpus Callosum 2. Anterior Commissure 3. Posterior Comissure 4. Hippocampal commissure

What is Corpus Callosum?

1. most prominent mammalian fibre system 2. Compact 3. 300 million axons 4. Connects most of the cortical areas, homologous and heterotypical areas

What are examples of Topography (post-mortem)?

1. Tracer 2. Histology 3. Wallerian Degeneration

What are examples of Topography (In vivo)?

1. Lesion/resection 2. Electophysiology 3. Imaging - DTI/fMRI

What are the classic segmentation of corpus callosum?

1. Rostrum 2. Genu 3. Body 4. Isthmus 5. Splenium However, no landmarks

What are connected by larger, more myelinated fibres?

Areas requiring fast conduction, the auditory, motor and visual areas

What are connected by smaller, less myelinated fibres?

Specialised cognitive regions

What does segment I of Corpus callosum contain?

prefrontal, premotor and supplementary motor

What does segment II of Corpus Callosum contain?

Anterior midbody contains the motor fibres

What does segment III of Corpus callosum contain?

The posterior midbody contains fibres to sensory and posterior parietal region

What does segment IV and V contain?

The isthmus and splenium contain fibres to the posterior parietal, temporal and occipital lobes

What does the correspondence rate maps represent?

represent inter-individual variability of fiber connections Body and dorsal splenium high reliability of dominant CC connection maps (sup frontal & parietal cortex) Ventral splenium low reliability (temporal cortex)

What are the Interhemispheric transfer deficit?

Middle genu Simple bimanual tasks Ant genu Complex bimanual tasks Ant body Deficient tactile localisation Subclinical deficits

What is evolutionary concept of lateralisation?

Increased brain size decreased Inter & increased Intra-hemispheric connectivity Tract loss (vent prefront; vent temp cortex) Extend new function to opposite hemisphere whilst retaining old function in original one

What are the indications for preoperative visualisation of WM tracts?

1. Plan surgery 2. Inform patients 3. Common tumours, epilepsy