This area of the brain acts as a kind of bridge between both hemispheres.
It is a compact structure that acts as a “bridge” between the hemispheres of the brain, and is located at the bottom of the interhemispheric fissure and on the septum pellucidum and the lateral ventricles.
Let’s see what are the characteristics of this component of the brain and what functions it performs.
- Recommended article: “Limbic system: definition, anatomy, structures and functions”
What is the corpus callosum?
The corpus callosum is an elongated structure arranged perpendicular to the interhemispheric fissure, so that each of its ends enters a different hemisphere.
It is, fundamentally, a nervous tract composed of commissural fibers . Let’s take a closer look at what these terms mean.
The corpus callosum as a tract
A nervous tract is a set of neurons that project in the same direction, keeping parts of the nervous system of the central nervous system connected to each other.
Its analogous structure in the peripheral nervous system are the nerves , which are very similar to these both in structural characteristics and in their functions: send nerve impulses from one side to another, so that the information from an information processing nucleus passes to another and this one can continue processing it and acting accordingly.
In this way, the nerve tracts have the appearance of “bundles” of neurons that travel together, more or less parallel but staying within the confines of a compact formation. Now, both the corpus callosum and the rest of the nerve tracts share the characteristic that they are made up of something called “white matter”.
What does this mean? Beyond describing the appearance that these structures have if we observe them with the eye (because they seem much paler than the rest of the areas of the brain), this term indicates that the presence of myelin in these areas is greater.
Myelin is a set of nerve cells belonging to the category of glial cells that cover the axon of neurons, that is, its longest part and that connects the neuronal soma (the body of the neuron, which contains its nucleus) with other nerve cells to which it is possible to send a nerve impulse. Its main function is to allow electrical signals to be channeled and travel more quickly around the axon, by keeping it isolated from its surroundings.
Thus, the corpus callosum is not simply composed of groups of neurons crammed together. It is made up of a group of very specific parts of these cells : the axons, whose appearance is whitish due to the myelin that covers them, thus contrasting with the gray matter that forms the cerebral cortex (in which the bodies of the neurons predominate). , and not so much the axons).
The corpus callosum as a bundle of commissural fibers
Another feature we have seen about the corpus callosum is that it contains commissural fibers . This simply means that the bundles of axons that form it do not travel in any direction, but rather in a very specific direction: from one cerebral hemisphere to the other, in both directions.
Bearing in mind that the anatomy of the brain is characterized by the existence of two cerebral hermispheres, one on the left and the other on the right, and that these are relatively isolated from each other (since they are separated in a large part of their surface by the interhemispheric fissure ), we can already begin to intuit that the commissural fibers matter a lot, because information travels through them that only have very limited points to access the other side of the brain.
But we will see this in a more detailed way in the next section.
Parts and internal structure
Despite the fact that the corpus callosum appears to be a compact and relatively homogeneous structure, the truth is that it is possible to distinguish several parts that compose it .
These parts of the corpus callosum are, in order from the most frontal end to the most occipital end, the rostrum, the genu, the trunk, and the splenius.
1. Rostrum
The rostrum is the end of the corpus callosum closest to the frontal lobes , and it narrows as it projects below the septum pellucidum, the membrane that keeps the two lateral ventricles apart. It maintains a relatively direct connection with the optic chiasm.
2. Genu
The genu, or knee of the corpus callosum , is so named because it curves very sharply downward and backward, so that it is slightly closer to the cerebral lobes than the rostrum. Nerve fibers that connect the prefrontal cortices of the left and right hemispheres cross through it.
3. trunk
The trunk is just behind the genu, and connects to the fornix and septal area , so that subcortical structures can send information to both hemispheres.
4. Asplenium
The splenius is easy to distinguish from the other parts of the corpus callosum because it is the posterior end , which is attached to the isthmus of the cingulate gyrus and has a rounded end. It has neural associations with the temporal and occipital lobes of each hemisphere, and with the pineal gland.
Functions
As can be inferred from what has been seen so far, the main function of the corpus callosum is to communicate areas of the brain between which there is a relatively large distance , and which are also located in areas located in different hemibodies. Compared to other structures of the brain in which the gray matter predominates, here the information is not processed as much, rather it is carried from one place to another.
In this way, it is possible for the brain to integrate information that must be processed as a whole, taking into account the work done by groups of neurons located on both sides of the brain.
In addition to this, if a certain area of a cerebral hemisphere is injured, it is believed that the corpus callosum allows the function previously performed by this disabled area to “migrate” to the other side of the brain, and be carried out by other nuclei of nerve cells. located there.
callosotomy
Callosotomy is what happens when, in a clinical or scientific context, the corpus callosum is sectioned so that it can no longer communicate between both sides of the brain. This is an important change in the functioning of the central nervous system, since although there are other interhemispheric commissures, the corpus callosum is by far the largest.
In general, when this happens (often as a last resort when it comes to mitigating the symptoms of very severe epilepsies) what is known as callous disconnection syndrome appears.
Among its main symptoms we find both motor coordination problems (for example, dressing) and perception of the environment, as a good part of the brain is divided into two halves isolated from each other. For example, the syndrome of the alien hand may appear, in which it is felt that one of the hands acts according to its own will, as if one could not control it.
Bibliographic references
- Doron, K.W.; Gazzaniga, M.S. (2008). Neuroimaging techniques offer new perspectives on callosal transfer and interhemispheric communication. Cortex; A Journal Devoted to the Study of the Nervous System and Behavior. 44(8): pp. 1023 – 1029.
- Candle, ER; Schwartz , JH & Jessell , TM (2001). Principles of neuroscience. Madrid: McGraw-Hill Inter-American.
- Von Plessen, K.; Lundervold, A.; Duta, N.; Heiervang, E.; Klauschen, F.; Smievoll, A.I.; Ersland, L.; Hugdahl, K. (2002). Less developed corpus callosum in dyslexic subjects—a structural MRI study. Neuropsychologia. 40 (7): pp. 1035 – 1044.
To the classic question “what do you do?” I always answer “basically I am a psychologist”. In fact, my academic training has revolved around the psychology of development, education and community, a field of study influenced my volunteer activities, as well as my first work experiences in personal services.