What is white matter of the brain?

[jayadds]

Hi all,

As stated above, what is white matter of the brain? Now, I have already read the standard definition for the term:

White matter is composed mostly of myelinated axons.

However, I seem to have difficulty understanding that concept. Is it trying to say that white matter is ONLY composed of myelinated axons? Am I right in thinking that there are no dendrites and cell bodies in the white matter? If so, does it mean that white matter is not made up of whole neurons but is actually made up of PARTS of a neuron? Perhaps I'm overthinking this a bit too much.

Many thanks,
Jay

 

[mazinse]

good question I would say mostly axons because axons can be super long and there are lots and lots of it, while dendrites are pretty small in comparison. the cells / tissues themselves are going to be just grey matter

 

[DiracPool]

White matter serves mostly as an "insulator" of long projection neuron tracts in the brain. It evolved to increase the conduction velocity of long range fasciculi such as the arcuate fasciculus which connects the left hemisphere language system in humans.

However, I seem to have difficulty understanding that concept. Is it trying to say that white matter is ONLY composed of myelinated axons? Am I right in thinking that there are no dendrites and cell bodies in the white matter? If so, does it mean that white matter is not made up of whole neurons but is actually made up of PARTS of a neuron? Perhaps I'm overthinking this a bit too much.

No, you're not overthinking it, it is an important question. There are two way axons become myelenated, 1) Schwann cells, which are glial cells that wrap their entire soma around an axon, and 2) oligodenrocytes, which have cellular projections that can wrap around several axons of different neurons. These are also glial cells. I don't believe the soma (cell body) and dendrites of neurons in general are myelinated. I'm just stating this from memory, so you might want to run a search on this to verify the details. There should be a good amount of data on it online.