White Matter - Lecture 3

Question 1

What is white matter composed of?

Answer 1

White matter is composed of glial cells and myelinated axons.

Question 2

What is the main function of myelinated axons?

Answer 2

Myelinated axons speed up the transmission of action potentials.

Question 3

How fast can axons transport neurotransmitters?

Answer 3

Axons can transport neurotransmitters at approximately 400 mm/day.

Question 4

What is the thickest axonal tract in the brain?

Answer 4

The corpus callosum, with around 404,150 fibers per mm².

Question 5

What is myelin and its main function?

Answer 5

Myelin is a multilayered glial membrane that insulates axons and enables saltatory conduction for rapid nerve transmission.

Question 6

What is saltatory conduction?

Answer 6

Saltatory conduction is the process where action potentials jump from one node of Ranvier to the next, speeding up signal transmission.

Question 7

When does myelination continue until?

Answer 7

Myelination continues well into the second decade of life.

Question 8

What are the interactions between myelinating cells and other brain cells?

Answer 8

Myelinating cells interact with neurons, astrocytes, and microglia, and axons depend on myelinating cells for support.

Question 9

What types of activities may counteract age-dependent myelin changes?

Answer 9

Motor, sensory, and social activities.

Question 10

What are projection fibers and their main function?

Answer 10

Projection fibers connect the cortex to distant regions like the subcortex or spinal cord. They help facilitate communication between the brain and other areas of the central nervous system.

Question 11

What are the two subclasses of projection fibers?

Answer 11

Corticothalamic/thalamocortical and corticofugal fibers.

Question 12

What structure do all projection fibers pass through?

Answer 12

The internal capsule.

Question 13

What are association fibers and their function?

Answer 13

Association fibers connect different cortical regions within the same hemisphere to facilitate communication.

Question 14

What is the function of the superior longitudinal fasciculus?

Answer 14

It connects the frontal, temporal, and parietal lobes and is involved in language processing (left hemisphere) and visuospatial learning (right hemisphere).

Question 15

What does a lesion in the inferior longitudinal fasciculus result in?

Answer 15

Visual amnesia, where a person cannot learn new information via the visual domain but can identify objects through other senses.

Question 16

What is the role of the cingulum?

Answer 16

The cingulum connects the prefrontal, parietal, and occipital lobes to the temporal lobe and hippocampus and is involved in attention, memory, and emotions.

Question 17

What can lesions in the cingulum cause in monkeys?

Answer 17

Apathy and indifference to surroundings and the group.

Question 18

What is the function of the uncinate fasciculus?

Answer 18

It connects the anterior temporal lobe to the orbital frontal regions and may play a role in mnemonic associations and decision-making.

Question 19

What is the corpus callosum, and what is its function?

Answer 19

The corpus callosum connects the two brain hemispheres, allowing communication between them. It is mostly symmetrical but has some asymmetrical parts.

Question 20

What are common symptoms of corpus callosum dysgenesis?

Answer 20

Mental retardation (60%), visual problems (33%), speech delay (29%), seizures (25%), and abnormal muscular tone (25%).

Question 21

What is the anterior commissure, and what does it connect?

Answer 21

The anterior commissure connects the two temporal lobes and serves as a reference point for the Talairach atlas.

Question 22

What is the role of the posterior commissure?

Answer 22

It connects the pre-tectal areas of the rostral midbrain and is involved in early visual processing.

Question 23

What is multiple sclerosis (MS), and how does it affect white matter?

Answer 23

MS is an immune-mediated disorder that targets and damages myelin, forming scar tissue (sclerosis) and causing various symptoms.

Question 24

What are some methods used to measure white matter in animals?

Answer 24

Tracer injections and fluorescent proteins.

Question 25

What imaging techniques are used to study white matter in humans?

Answer 25

Polarized light imaging and Diffusion Weighted Imaging (DWI).

Question 26

What does Diffusion Weighted Imaging (DWI) measure?

Answer 26

DWI measures the mobility of water molecules, which is affected by barriers like myelin.

Question 27

What is tractography, and how is it related to DWI?

Answer 27

Tractography is a process that models DWI data to estimate the presence and direction of white matter tracts.

Question 28

What are some limitations of Diffusion Weighted Imaging (DWI)?

Answer 28

Low resolution (e.g., 2mm³ voxel size), inability to measure true white matter integrity or anatomical tracts, and limitations in detecting multiple crossing fibers in one voxel.