White matter of the brain: structure and functions
The human brain is a complex structure. If we observe it from the outside, we see a gelatinous mass of an approximately grayish color, with numerous protrusions, grooves and convolutions that cover its surface. Inside, however, a series of whitish structures can be seen.
This change in coloration is not accidental: the neurons that make up the brain have different parts with different functions, their existence having been delimited of two types of matter or substances throughout the nervous system: the gray matter, in which we mainly find somas or nuclei of neurons, and white matter, also called white matter.
The white matter
The white matter is that part of the nervous system mainly configured by neuron axons, that is, the part of the neurons in charge of transmitting the information processed by the soma through the rest of the system. While the gray matter (also called Gray matter) is especially visible in the cerebral cortex and inside the spinal cord, white matter can be found more easily in the internal structures of the brain and in the outermost part of the spinal cord.
The whitish color of this substance is due to the presence of myelin, a substance that covers the axons of a large part of the neurons. This myelin has as its main function to accelerate the transmission of information. This acceleration is due to the fact that, thanks to myelin, the information does not have to pass in a straight and continuous way through the axon, Instead, it is carried out through small jumps between the myelin sheaths (this type of communication).
Basic functions
The main function of the white matter is the correct transmission of brain information. This substance has a great implication at the time of allowing the human being to transfer the electrochemical pulses emitted by the brain to the rest of the body. In this way we can consider that it coordinates communication between the different systems of the human body, both inside and outside the brain. Thanks to it, distant parts of the nervous system can maintain the necessary contact to work together.
That is why where there is white matter, the axons of neurons especially predominate, which means that These areas of the brain that are white are essentially neuronal highways, communication areas between parts of the brain.
Other recently discovered features
Traditionally, it has been assumed that what we have seen is the main function of white matter, believing this a passive element that was limited to transfer the orders of the nucleus of the neuron to other cells. However, more recent research indicates that white matter, apart from the mere transmission of information, is related to different cognitive and emotional elements.
This is because the connection and speed offered by the substance allows the construction of neural networks that can govern different processes. Specifically, it greatly affects memory and learning, as well as the management of cognitive resources and executive functions. Thus, it has been indicated that the white matter greatly affects the development and use of intelligence.
Structure and internal configuration
As we have indicated, the white matter is predominantly made up of myelinated axons, which are part of the neuron in charge of projecting the nerve impulse towards relatively remote areas, with the maximum speed and efficiency. This does not mean that somas, or even axons without myelin cannot be found, but their proportion is very high. less than those of the gray matter, which produces the visual effect that white predominates in those regions.
Apart from these components, it also contains a high number of glial cells, structures that support and maintain neurons. Myelin is not the only substance associated with these glial cells, there is a great variety of these that serve to keep neurons in proper functioning.
Tracts of the brain
Both inside and outside the central nervous system, the white matter is organized in the form of bundles of nerve fibers. The so-called projection tracts or nerve fibers send the information processed by the gray matter to the different body regions located outside the brain. A second type of white matter fibers are the association fibers connecting different brain regions of the same hemisphere. The third and last type corresponds to the interhemispheric commissures, which connect structures from different hemispheres.
Within the brain there are a large number of structures configured mainly by white matter. One of the most visible and notable is the corpus callosum, one of the highly relevant interhemispheric commissures that joins the two cerebral hemispheres and transmits information between them.
When the white matter fails
As we already know, there are numerous neurological disorders caused by damage to brain structures. Considering that the processing speed is largely due to the presence of myelin and the need for information to travel effectively and efficiently in order to coordinate our actions, the presence of damage to the white matter can cause disorders such as the following: tiredness, psychomotor slowness, incoordination and muscle weakness, blurred vision, difficulty in remembering, deficit in Executive functions and intellectual abilities are some of the frequent symptoms of poor functioning of the white matter.
Some of the disorders that affect or are affected by the white matter are multiple sclerosis (in which there is an inflammation of the white matter that produces a demyelination of neurons), Alzheimer's and other dementias, ADHD (A lower amount of white matter has been observed in subjects with this disorder) or the dyslexia (The difficulties with the processing speed being linked).
Bibliographic references:
Fields, D. (2008). White Matter Matters. Scientific American, p. 54.
Tirapau-Ustarroz, J., Luna-Lario, P., Hernáez-Goñi, P., & García-Suescun, I. (2011). Relationship between white matter and cognitive functions. Journal of Neurology, 52 (12), 725-742.
