Cerebral White Matter

What kind of scan is this

Tractography

Myelin is formed by what where

Myelin formed by Oligodendrocytes - wraps around axons

How do we look at diffusion of molecules through the axons

Diffusion MRI

Why is diffusion MRI used in stroke

You see a spot where the microstructure of fibres is destroyed with a shadow around it - site of stroke

No motion = tissue that won’t be recovered

What part of this is grey/white matter

Circled = grey matter

The rest = white matter

What technique is used to examine the brain post mortem

Klinger Technique

Why does the 1 week old brain look different on an MRI

Note much white matter - develops over time

At birth the brain myelination is minimal

It increases dramatically during the first and second year and continues to mature through life peaking at approximately 40 years

It then begins to degenerate thereafter

Striae defn

thin bundles of fibers that pass longitudinally across the brain

(white matter)

Fascicles defn

microscopically determined groups of fibers

You can have multiple tracts through a fascicle

Tracts defn

groups of axons subserving a similar or corresponding function

Lamina defn

relatively thin sheets of axons that proceed in a similar direction

Capsules

curved sheets of fibers that partially enclose a grey matter structure

Radiations

broad sheets of fibers that arch together to/from one target

How are white matter tracts categorised

Commissural: Crossing the midline connecting cortical areas in one hemisphere to the other

Projection: Cortex to distant sites such as brainstem and spinal cord and visa versa

Association: Connecting cortical areas within the same hemisphere

What categories of white matter tracts are seen here (what colour)?

Commissural = green

Projection fibres = purple

4 types of commissural white matter tracts

• Corpus Callosum

• Anterior Commissure

• Posterior Commissure

• Hippocampal Commissure

Location of the Anterior Commissure

Located on lamina terminalis

Posterior Commissure location

Epithalamic commissure

ACPC line

Hippocampal Commissure location

Commissure of the fornices

What do homotopic & heterotopic commissural fibres mean

Homotopic fibers are those that connect corresponding areas of cortex

Heterotopic fibers connect a non-corresponding area in the contralateral hemisphere

Corpus Callosum is Major white matter connecting the hemispheres. Name the 5 parts of it

• Rostal

• Genu

• Body

• Isthmus

• Splenium

Projection white matter tracts convey impulses from where to where

Projection fibers convey impulses from the cortex to distant sites or from distant sites to the cortex

Projection fibres pathway

Many fibers pass reciprocally through the brainstem (crus cerebri/cerebral peduncles) → travel compactly through the internal capsule at the basal ganglia level → relay in the thalamus → and finally reach the cortex

Allows for organized communication between the cortex and subcortical structures.

What are the 5 parts of the internal capsule

• Anterior Limb

• Genu of the IC

• Posterior Limb

• Retrolenticular part (Contains optic radiations)

• Sublenticular (Contains auditory radiations)

Capsules can be internal, external or what?

Extreme

Medullary Lamina are Middle, Lateral, and what is the last one called & its location

Internal - within thalamus projection

What is Corona radiata

Corona radiata is not a specific tract!

It is the collective term for all the fiber tracts connecting the brainstem to the thalamus (including the internal capsule area) and those connecting the thalamus and cortex termed thalamic peduncles

Name the thalamic peduncles

What is a stria

a tract or pathway — a visually or anatomically distinct band of axons connecting one part of the brain to another

Name the 4 main striae of the brain

• Olfactory Striae (CN1)

• Stria Medullaris

• Stria Terminalis

• Medial & Lateral Longitudinal Striae

Role of association fibres

Association fibers connect diverse regions of the same hemisphere

Fill in the names of the association fibres

What association fibres are shown in the first image and as the blue in the second image

Inferior Longitudinal Fasciculus (ILF)

What does the Inferior Longitudinal Fasciculus (ILF) connect

Connects inferior posterior temporal and occipital cortices to anterior temporal areas both lateral and medial

Function of the the Inferior Longitudinal Fasciculus (ILF)

Object and face recognition

What association fibres are shown as blue in the first image and green in the second image

Inferior Frontal Occipital Fasciculus (IFOF)

What does the Inferior Frontal Occipital Fasciculus (IFOF) connect

Connects broad areas of the temporal lobe and inferior occipital lobe to the frontal lobe

Function of the the Inferior Frontal Occipital Fasciculus (IFOF)

Object recognition, visuospatial and semantic processing

What association fibres are shown here

Uncinate Fasciculus

Describe the location & projection direction of Uncinate Fasciculus

Fibers arise anterior temporal lobe and curve to frontal areas

Uncinate Fasciculus functions

involved in processing novel information and emotional valence of stimuli

The ILF serves as the main white matter pathway linking the visual occipital areas to what, enabling high-level visual recognition and memory integration

The ILF serves as the main white matter pathway linking the visual occipital areas to the fusiform cortex, enabling high-level visual recognition and memory integration