The brain is made up of two types of material. So we know the white matter and gray matter of the brain.

In the central nervous system, the gray matter corresponds to an accumulation of neuron cell bodies. The white matter, when it is formed by bundles of axons. The type of matter constituting the brain plays a very important role in its functioning.

Nerve tissue consists of nerve cells, the neurons, which are surrounded by a supporting tissue. This support tissue is composed of different cells (astrocytes, oligodendrocytes) that are grouped under the name of glial cells.

Neurons are formed of a cell body and multiple extensions. The main extension is called axon and is used to condense nerve impulses.

In this article, we will mainly address the subject of the white matter of the brain. What is the white matter of the brain? What are these characteristics of the white matter of the brain? What is the structure of the white matter of the brain? What are the functions of the white matter of the brain? What are the disorders related to the white matter of the brain?

Then we will finish with the answers to the following questions: What is the gray matter? What are the functions of the gray matter?

I – The White Matter of BrainThe white matter and gray matter of the brain and spinal cord are nervous tissues.

The white matter is a whitish tissue that is part of the central nervous system. Located in the brain and spinal cord, it consists of axons – extensions of neurons that carry electrical signals to synaptic areas – and neuroglia – tissue that supports nerve cells -.

These are millions of communication cables, each containing a single long wire, or axon, surrounded by a white fatty substance, called myelin. Like the lines that connect phones in different cities, these white cables connect neurons from one region of the brain to another.

II – The Characteristics of the White Matter of the Brain

The white matter is mainly characterized by a region of the brain that does not contain neural nuclei.

The white matter is a whitish part of the central nervous system tissue. It is located mainly in the spinal cord and is formed by extensions of neurons that carry electrical signals to synaptic regions and by glial cells.

The white matter forms the inner part of the brain and constitutes more than half of the two hemispheres of the brain. The brain is essentially composed of all the nerve fibers of wiring covered with a white matter, called myelin. Like the tangle of telephone lines in a city, these cables connect neurons in one area of the brain to the other, which is essential for the brain to function as a whole.

The role of the white matter is to ensure a good flow of information in the nervous system and connect the different regions of the brain. For this reason, the white matter is characterized in that it contains high amounts of myelin.

*** Myelin

Myelin is an essential fatty membrane that isolates every nerve in the brain and spinal cord as a plasticized sheath surrounds an electrical wire.

For decades, neuroscientists have had little interest in white matter. They considered myelin as a simple insulator and axons as commonplace passive pathways. The theories of learning, memory, and psychic disorders were based on molecular mechanisms occurring in the cell bodies of neurons and in synapses – points of contact between neurons.

Myelin gives color to the white matter that coats the axons. For more than a century, neuroscientists have observed neurons under the microscope and have seen long fibers, the axons, connecting cell bodies to each other. Each axon is surrounded by a thick crystalline gel. The anatomists have supposed that this coating of fatty substance made it possible to isolate the axons, like the insulation of a wire. However, many axons, especially the smaller ones, did not have myelin. And even along the myelinated fibers, the insulation had holes almost every millimeter. These places devoid of myelin are nodes of Ranvier, named after the French anatomist Louis-Antoine Ranvier who was the first to describe them.

Neurons communicate with each other by sending electrical signals – move about 100 times faster along axons when they are enveloped in myelin. It is produced in leaflet form by two types of glial cells – cells of the nervous system that are not neurons -. An octopus-shaped glial cell called an oligodendrocyte, envelops neurons in the brain. Electrical signals, unable to cross the sheath, jump rapidly along the axon from one node to another. In the peripheral nerves and the spinal cord, it is a sausage-shaped glial cell, called a Schwann cell, that produces myelin.

Without myelin, electrical leaks take place along the axon and the signal dissipates. In order for the conduction velocity to be maximal, the thickness of the insulator must be proportional to the diameter of the axon. It is not known how oligodendrocytes “know” whether 10 or 100 layers of insulation are needed to create the appropriate thickness on axons of different diameters.

*** Myelinization in the Adolescent Brain

The process of coating myelin axons is produced at different ages. At birth, myelin is only seen in a few areas of the brain, and since then the process has begun to spread to reach its peak between 25 and 30 years of age.

One of the most common areas of myelinization at this time is the corpus callosum that connects the two hemispheres of the brain. This area of the brain is involved in high-level thinking and creativity. In addition, this myelination is progressively from the back of the brain forward. The first regions concerned are the limbic areas of the emotions generated by the perceptions of the outside world. The last regions concerned are the frontal areas which are those of abstract reflection and the distancing of the real world.

The adolescent brain is only connected with local connections, unlike the adult brain that is connected with remote and better-distributed areas. The adolescent brain has not reached maturity and its responses are different from those of adults, particularly with respect to the frontal lobe. The development of the brain is achieved with the total thickness and coating of the axons, which is proper to the adult brain. When axons reach their final myelination, behavioral abnormalities will be more limited.

The myelination of the adolescent brain is an improvement in cognitive abilities, including memory and reading skills. Myelinization also allows, since the center of the language is distributed in two hemispheres, to communicate more quickly. The body movements coordinated by the brain become faster.

The increase of the white matter enhances the efficiency of the prefrontal lobe, the lower part of the frontal lobe, where the seat of intellectual and emotional capacities, such as memory, decision-making, and behavioral control, is located. Its maturation also confers, in particular, the capacities of abstract thought, such as the deduction, the generalization or the handling of new concepts.

It is at the time of adolescence that the stock of neurons and synapses for a lifetime will be constituted and structured. This stock is not fixed, the neuronal plasticity shows that within this stock reorganizations are always possible and sometimes in a massive way.

The result is new intellectual possibilities and new poles of interest for adolescents who often discover other areas and this is where they begin to form their own opinion.

III – The Structure of the White Matter

The white matter portion of the brain accounts for about 60 percent of the total brain volume.

The cerebral white matter is mainly composed of myelinated axons grouped into bundles. The white matter is formed of fibers. The cell and the fiber are only two parts of the same essential elements of the nervous system: the neuron.

Projection nerve fibers send information processed by the gray matter to different regions of the body out of the brain. The second type of white matter fibers in association fibers that connect different regions of the brain of the same hemisphere. The third and last type corresponds to the inter-hemispheric binding commissures that connect the structures of two hemispheres.

In the brain, there is a large number of structures consisting mainly of white matter. One of the most visible and remarkable is the corpus callosum, one of the inter-hemispheric commissures that connect the two cerebral hemispheres and transmits information between them.

It is known that the structure of the white matter can be modified under the effect of exercise, for example by reading or various cerebral training. This is called brain plasticity.



The Behavioral Neurology of White Matter

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IV – The Functions of the White Matter

Its function is to allow communication between the different areas of the cerebral cortex or between the cortex and the rest of the central nervous system.

In addition, it controls functions that the body is not aware of, such as temperature, blood pressure, and heart rate. She is responsible for the release of hormones and manages the control of hunger and thirst, and emotions.

For a long time, researchers have considered the cerebral white matter very little and considered that its role was only passive and that the myelin which gave it its color, was a protein that wraps the connecting cables of the neurons, acting as an insulator, which is true. According to them, the process of learning, memory and all the functions of the brain corresponded to molecular actions produced only in neurons, which is also true.

It can be determined that white matter is responsible for coordinating communication between different systems of the human organism. This involves the two regions inside and outside the brain. It is for this reason that in the white matter predominate axons of neurons because it is the part capable of transmitting the information to another neuron.

The white matter acts as a bridge of communication between the different regions of the brain containing the neuron cells. These areas of the brain are, in essence, the neural routes, the areas of communication and transmission of information between brain regions.

It has recently been discovered that white matter has more functions than previously thought, such as building fast neural networks that help in the process of memory, learning and overall our cognitive resources for the development of intelligence.

This is how new experiments have shown that white matter is modified in relation to environmental factors and varies in individuals as they acquire different experiences or develop certain skills, such as learning to play the game piano. In other words, the white matter undergoes changes when the gray matter develops new activities, be they mental or social.

The white matter is closely related to cognitive and emotional processes, and today it is recognized that it is an important element in the exercise of these actions.

In fact, the neural networks generated by the white matter seem closely related to memory and learning activities. In addition, they participate in the management of cognitive resources and executive functions.

Today, it is recognized that white matter is a very important element of the brain that greatly affects the development and use of people’s intellectual abilities.

V – White Matter Disorders

In recent times, many neuroscientists have found circumstantial evidence that suggests that not only is gray matter to blame for some mental illnesses, but the white matter is also implicated in these abnormalities. There are many neurological disorders caused by damage to brain structures. White matter abnormalities due to myelination defects are thought to affect inter-neuron connections.

1 – Dyslexia

Patients who suffer from dyslexia have reductions in the volume of white matter. Dyslexia is ultimately due to impaired transmission, by changing the times in the system of connected circuits needed to read correctly. Thus brain scans of brain imaging revealed a decrease in the volume of the white matter precisely in these pathways. There is strong evidence of cortical area dysfunction syndrome corresponding to reading and spelling.

2 – Attention Deficit

A smaller volume of right frontal white matter is correlated with the variation in children’s sustained attention with attention deficit disorder.

3 – Cognitive Disorders of the Speed of Information Processing

The executive function is a set of cognitive operations supported by the activity of the most complex systems of the frontal lobes. These operations are responsible for planning, goal setting, classification, initiation, implementation, monitoring, flexible changes and confrontation of all mental functions.

Episodic memory represents events or facts relating to the details of the situations of life. These are memories of the times and places where the events occurred and which serve to organize them. It is generally opposed to semantic memory. The latter would serve to store the meaning of the words and relations of these meanings; the organization and retrieval of information are carried out from its meaning, while episodic memory is not involved in its organization or recovery.

Decreasing processing speed means greater inefficiency in all tasks that other higher functions face, resulting in less efficient coding of stimuli.

Since the speed of treatment is largely due to the presence of myelin and the need for information to travel efficiently and effectively to coordinate our actions, the presence of lesions in the white matter can cause disorders such as fatigue, psychomotor retardation, incoordination and muscle weakness, impaired vision, memory problems, executive function deficits, and intellectual abilities. These are some of the most common symptoms of white matter dysfunction.

4 – Schizophrenia

Schizophrenia is due to abnormal connectivity. The antecedents are of different types. In recent years, more than 20 research papers have been published concluding that white matter in schizophrenia appears abnormal in many areas of the brain. There would be fewer oligodendrocytes. It has also been shown, by comparing genes by electronic chips, that those related to schizophrenia, are the same ones that are engaged in the formation of myelin.

5 – Other Disorders

Finally, thanks to the technique applied to ADHD, abnormalities in the white matter have been found to be associated with bipolar disorder, as well as language disorders, autism, cognitive decline, and aging. Alzheimer’s disease. Some disorders that affect or are affected by the white matter are multiple sclerosis, in which inflammation of the white matter produces demyelination of neurons.

Another pathology affecting the white matter is the development of a leukoaraiosis which is a rarefaction of the white matter due to several conditions, including the attack of the blood-brain barrier.

It is very possible that in the years to come, with the advancement of knowledge, we continue to confirm dysfunctions translated into brain diseases due to alterations, both of the gray matter and the white matter.

VI – The Gray Matter of the Brain

The gray matter is a greyish central nervous system tissue. It is localized in the encephalon and the spinal cord. It is a complex structure composed of nerve cells and nerve cells, neuroglia (interstitial tissue that protects the cells).

The gray matter appears gray-brown due to the presence of neuronal cell bodies and capillaries, as well as the relative lack of myelin.

In the brain, gray matter is on the surface of the cerebral cortex and the cerebellum. It is also found in the deepest parts of the brain, particularly the basal ganglia, the thalamus, the hypothalamus, the subthalamic nuclei, and others.

The substance – or gray matter – is the place of mental operations and the storage of information. It occupies about 40% of the entire human brain and consumes 94% of the oxygen.

VII – The Functions of the Gray Matter

The gray matter contains most of the cell bodies of the brain. It is found in areas of the brain involved in muscle control and sensory perception – such as seeing and hearing – memory, emotions, speech, decision-making, and self-control.

The role of gray matter is to receive messages, review information and prepare responses. Some diseases (such as Alzheimer’s disease) are caused by lesions of the gray matter of the cortex.

The gray matter of the spinal cord is divided into three columns:

– The anterior gray column contains motor neurons. These cells are responsible for the movement of the muscles.

– The posterior gray column contains the points of synapses of the sensory neurons. These receive sensory information from the body, including touch, proprioception, and vibration. This information is sent from skin, bone and joint receptors by sensory neurons whose cell bodies are located in the dorsal root ganglion. This information is then transmitted in the axons to the spinal cord, including the dorsal-medial column and the spinothalamic tract.

– The gray lateral column is the third column of the spinal cord.

Note: The gray matter of the spinal cord can be divided into different layers, called Rexed partitions.

It is in the gray matter where all information is stored, and in which reside memory and intelligence. It consists of dense cell tissue of neurons, which decide all brain activity.

By Way of Conclusion: Comparison Between the White Matter and Gray Matter of the Brain

The gray matter consists of the bodies of nerve cells, and the white matter consists of fibers.

Unlike the white matter, the neurons of the gray matter do not have extended axons.

The gray matter occupies 40% of the brain, while the white matter occupies 60% of the brain. The gray matter, however, consumes more power and consumes about 94% of the total oxygen to the brain.

The gray matter has a gray color because of the gray nuclei of the cells. Myelin is responsible for the white appearance of the white substance.

The information processing is done in the gray matter, while the white matter allows the communication between the different areas of the gray matter and between the gray matter and the other parts of the body.

The gray matter does not have myelin sheaths, while the white matter is myelinated.

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