White Matter - Lecture 3 Flashcards
What is white matter composed of?
White matter is composed of glial cells and myelinated axons.
What is the main function of myelinated axons?
Myelinated axons speed up the transmission of action potentials.
How fast can axons transport neurotransmitters?
Axons can transport neurotransmitters at approximately 400 mm/day.
What is the thickest axonal tract in the brain?
The corpus callosum, with around 404,150 fibers per mm².
What is myelin and its main function?
Myelin is a multilayered glial membrane that insulates axons and enables saltatory conduction for rapid nerve transmission.
What is saltatory conduction?
Saltatory conduction is the process where action potentials jump from one node of Ranvier to the next, speeding up signal transmission.
When does myelination continue until?
Myelination continues well into the second decade of life.
What are the interactions between myelinating cells and other brain cells?
Myelinating cells interact with neurons, astrocytes, and microglia, and axons depend on myelinating cells for support.
What types of activities may counteract age-dependent myelin changes?
Motor, sensory, and social activities.
What are projection fibers and their main function?
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.
What are the two subclasses of projection fibers?
Corticothalamic/thalamocortical and corticofugal fibers.
What structure do all projection fibers pass through?
The internal capsule.
What are association fibers and their function?
Association fibers connect different cortical regions within the same hemisphere to facilitate communication.
What is the function of the superior longitudinal fasciculus?
It connects the frontal, temporal, and parietal lobes and is involved in language processing (left hemisphere) and visuospatial learning (right hemisphere).
What does a lesion in the inferior longitudinal fasciculus result in?
Visual amnesia, where a person cannot learn new information via the visual domain but can identify objects through other senses.
What is the role of the cingulum?
The cingulum connects the prefrontal, parietal, and occipital lobes to the temporal lobe and hippocampus and is involved in attention, memory, and emotions.
What can lesions in the cingulum cause in monkeys?
Apathy and indifference to surroundings and the group.
What is the function of the uncinate fasciculus?
It connects the anterior temporal lobe to the orbital frontal regions and may play a role in mnemonic associations and decision-making.
What is the corpus callosum, and what is its function?
The corpus callosum connects the two brain hemispheres, allowing communication between them. It is mostly symmetrical but has some asymmetrical parts.
What are common symptoms of corpus callosum dysgenesis?
Mental retardation (60%), visual problems (33%), speech delay (29%), seizures (25%), and abnormal muscular tone (25%).
What is the anterior commissure, and what does it connect?
The anterior commissure connects the two temporal lobes and serves as a reference point for the Talairach atlas.
What is the role of the posterior commissure?
It connects the pre-tectal areas of the rostral midbrain and is involved in early visual processing.
What is multiple sclerosis (MS), and how does it affect white matter?
MS is an immune-mediated disorder that targets and damages myelin, forming scar tissue (sclerosis) and causing various symptoms.
What are some methods used to measure white matter in animals?
Tracer injections and fluorescent proteins.
What imaging techniques are used to study white matter in humans?
Polarized light imaging and Diffusion Weighted Imaging (DWI).
What does Diffusion Weighted Imaging (DWI) measure?
DWI measures the mobility of water molecules, which is affected by barriers like myelin.
What is tractography, and how is it related to DWI?
Tractography is a process that models DWI data to estimate the presence and direction of white matter tracts.
What are some limitations of Diffusion Weighted Imaging (DWI)?
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.
