Bales: White matter systems

Question 1

What is a radiation?

Answer 1

A “radiation” is usually a projection from a more localized area to a broader area

For example, both auditory and visual systems have radiations

Question 2

What are commissures and decussations?

Answer 2

Tracts connecting the same structures or areas are usually called “commissures”

Tracts connecting different structures or areas are usually alled “decussations”

Question 3

What do short fascicle interconnect?

Answer 3

close cortical regions

can be called “arcuate” or “U” fibers

Question 4

What connects Broca and Wernicke’s areas? What would a lesion in this region cause?

Answer 4

arcuate fasciculus

a lesion here would cause a conduction aphasia

Question 5

What does the inferior longitudinal fasciculus connect?

Answer 5

occipital and temporal lobes

Question 6

What connects the anterior temporal and the lower frontal lobes?

Answer 6

the uncinate fasciculus

Question 7

What does the anterior commissure connect?

Answer 7

The anterior temporal lobes

Question 8

What is the function of the corpus callosum? What parts of the corpus callosum are larger?

Answer 8

corpus callosum fibers interconnect similar areas in opposite hemispheres

the rostral and caudal ends are larger in area because they accommodate more fibers (forceps minor (anterior) and major (posterior))

Question 9

Where is there more likely to be a dysgenesis of corpus callosum and why?

Answer 9

the splenium will always be affected because the corpus callosum develops from front to back

Question 10

What will result from a full callostomy?

Answer 10

Normally, visual info from the right occipital lobe (left visual field) gets to Broca’s on left via corpus callosum. Without splenium, patient can’t read aloud words in left visual field.

the splenium is normally spared when preforming a callostomy for intractable epileptic seizures to avoid this

Question 11

What is the corona radiata? What is its name when it passes between large gray meter nuclei? What is it continuous with inferiorly?

Answer 11

fibers to and from cortex and lower (subcortical) structures (e.g., thalamus, brainstem, and spinal cord)

between the lentiform nucleus and the thalamus and caudate nucleus, it is called internal capsule

inferiorly, the internal capsule is continuous with the crus cerebri (of the cerebral peduncle of the midbrain)

Question 12

What structures encapsulate the lentiform nucleus?

Answer 12

the external (laterally) and internal capsule (medially)

Question 13

What are the layers surrounding the lentiform nucleus on the lateral side before it reaches the insula?

Answer 13

medial to lateral:
(lentiform nucleus)
external capsule
claustrum 
extreme capsule 
(insula)

Question 14

What does the centrum semiovale contain fibers from?

Answer 14

the internal capsule, callosal fibers and the superior longitudinal fasciculus

Question 15

When does myelination start and end?

Answer 15

starts prenatally and finishes after the 2nd year

sensory (dorsal) myelinate ahead of motor (ventral) in the spinal cord and projection is myelinated before association pathways

the spinal cord myelinates before the brainstem

brainstem myelinated caudal–> rostral

after 2 y.o, the U-fibers and association cortices are still myelinated

Question 16

What will the T2 MRI differences be in a 1 week old vs a 2 year old? Why is that?

Answer 16

The 1 week old will have hyperintense white matter

after myelination, the 2 year old will have mature white matter which is hypointense relative to gray (it will have more darkness on the MRI)

myelination reduces the relative water content of white matter (by increasing the lipid content) –> water shows up more white on an MRI

Question 17

What results from a posterior commissure lesion?

Answer 17

loss of vertical gaze (looking upward)