White substance 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 protuberances, grooves and circumvolutions that cover its surface. Inside, however, it can be observed a series of whitish color structures .
This change in coloration is not coincidental: the neurons that make up the brain have different parts with different functions, having defined the existence of two types of substances or substances throughout the nervous system: the gray substance, in which we mainly find Soma or nuclei of neurons, and the white matter, also called white matter .
The white substance
The white matter is that part of the nervous system configured mainly by axons of neurons, that is, the part of the neurons responsible for transmitting the information processed by the soma for 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, the white substance can be found more easily in the internal structures of the brain and in the outer part of the spinal cord .
The whitish coloration of this substance is due to the presence of myelin, a substance that lines the axons of a large part of 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, but rather it is done through small jumps between the myelin sheaths (denominated saltatoria transmission to 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 the 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, axons of neurons predominate, which means that these areas of the brain that are white are, in essence, neuronal highways , communication zones between parts of the brain.
Other functions recently discovered
Traditionally, it has been assumed that what we have seen is the main function of the white matter, believing it to be a passive element that limited itself to transferring the orders of the nucleus of the neuron to other cells. However, more recent research indicates that white matter, regardless of the mere transmission of information, it 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 affects to a large extent the development and use of intelligence .
Structure and internal configuration
As we have indicated, the white matter is predominantly formed by myelinated axons, which are the part of the neuron responsible for projecting the nervous impulse to relatively distant areas, with maximum speed and efficiency. This does not mean that somas can not be found, or even axons without myelin, but their proportion is much smaller than those of the gray matter, which produces the visual effect of the predominance of white in those regions.
Apart from these components, It also contains a high amount of glial cells, structures that support and maintain the neurons . Myelin is not the only substance associated with these glial cells, there is a wide variety of these that serve to keep neurons functioning correctly.
The tracts of the brain
Both inside and outside the central nervous system, the white matter is organized in the form of sets of nerve fibers . The so-called tracts or nerve fibers of projection send the information processed by the gray matter to the different body regions located outside the brain. A second type of fibers of white substance are the fibers of association connect different brain regions of the same hemisphere . The third and last type corresponds to the interhemispheric commissures , which connect structures of different hemispheres.
Within the brain there are a large number of structures configured mainly by white matter. One of the most visible and remarkable is the corpus callosum, one of the interhemispheric commissures, of great relevance that unites the two cerebral hemispheres and transmits the information between them.
When white matter fails
As we already know, there are numerous disorders caused by damage to the structures of the brain, of a neurological nature. Taking into account that the speed of processing is largely due to the presence of myelin and the need for information to travel effectively and efficiently to coordinate our actions, The presence of damage to the white matter can cause disorders such as the following: fatigue, psychomotor slowness, muscle incoordination and weakness, blurred vision, memory difficulty, deficits in executive functions and intellectual abilities are some of the frequent symptoms of white matter malfunction.
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 the neurons), Alzheimer's and other dementias, ADHD (in subjects with this disorder a lower amount of white substance has been observed) or dyslexia (the difficulties with the speed of processing being connectable).
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.
