Sylvian Fissure (brain): What It Is, Functions And Anatomy
Our brain is one of our most important and complex organs being full of different structures, areas and regions of great importance that govern different basic aspects for the maintenance of life.
These structures require a space to exist, a space that is limited by the bone structure that protects the organ: the skull. And some of these structures could be really large, as is the case with the cerebral cortex. Fortunately, throughout our development the brain compacts, the cerebral cortex growing in such a way that it forms different folds (which gives the brain its characteristic appearance). And with these folds the grooves between them also appear. One of the most famous is the lateral sulcus or Sylvian fissure
Before going into detail about what the Sylvian fissure is, we must stop for a moment and first consider how our brain is structured. In this way we will better understand the route that this cleft traces along the cerebral cortex.
Seen from the outside, the brain appears as a relatively compact mass, the cerebral cortex being full of folds in such a way that the whole of it fits inside the skull. The fact that these folds exist also generates the existence of different indentations, which are called fissures or grooves. The concave parts, those that stand out, are the gyri or convolutions.
Thus, the cerebral sulcus or fissure is considered to be that slit or hole left by the cerebral cortex when it folds in on itself during development and that, seen from the surface, gives an idea of what the limits of the brain lobes are.
The Silvio fissure: what is it and what areas does it separate?
The Sylvian fissure or lateral sulcus is, together with Rolando’s, one of the most visible and recognizable fissures or sulci of the human brain. It is located in the lower part of the two cerebral hemispheres and subsequently runs across a large part of the brain. This groove appears horizontally, being located on the naso-lambdoid line.
This is one of the most relevant grooves, since separates the temporal and parietal lobes and in its lower part the frontal and temporal lobes We are facing the deepest crevice that exists in the entire brain, to the point that in its depths hides the so-called fifth cerebral lobe: the insula. It also contains the transverse temporal gyrus, which is involved in the auditory system.
It is also worth noting that The middle cerebral artery, also called sylvanic artery, passes through it For this reason, it irrigates the different brain regions in the area.
This fissure is one of the first to appear throughout our development, already being visible in fetal development. Specifically, it can often be observed from the fourteenth week of gestation. Its morphology and depth will evolve as the fetus develops.
Branches
The Sylvian fissure can be divided into several branches, specifically in three main ones: ascending or vertical branch, horizontal branch and oblique trifurcation branch. The name of these gives an idea about their orientation.
Between the first and the second we can find the third frontal gyrus, and specifically the pars triangularis (corresponding to Brodmann area 45). In the horizontal branch the pars orbitalis (area 47) and the pars opercularis (corresponding to area 44) between the oblique and vertical trifurcation branches. These areas are associated with language production.
Diseases and disorders with alterations in this fissure
The Sylvian fissure is a groove that all or practically all human beings have. However, There are diseases in which this fissure does not form correctly or is altered for any reason. Among them we can find examples in the following pathologies.
1. Alzheimer’s and other dementias
Patients with Alzheimer’s usually present throughout the development of their disease an enlargement of the Sylvian fissure, this enlargement being a product of the degeneration of neuronal tissue. This anomaly can also be found in other dementias and neurodegenerative diseases, which over time kill nerve cells and cause the brain to appear withered, with large grooves and very pronounced folds. This means that its effects are not limited to the sylvian fissure, but are felt throughout the cortex in general.
2. The absence of cerebral sulci: lissencephaly
Lissencephaly is an anomaly generated throughout neurodevelopment in which the brain appears smooth and either without or with few convolutions and fissures, alteration caused by a deficit or absence of neuronal migration or by an excess of this This phenomenon may have genetic causes or be due to alterations produced during embryonic development.
It can present in two ways: the complete one, also called agyria, in which no cerebral gyri or sulci develop, and the incomplete or pachygyria in which some do exist, although they are few and very large. There is usually a poor covering of brain parenchyma in the Sylvian fissure.
In general, the prognosis is not good, and the disease is associated with a short life expectancy, presenting symptoms such as seizures, respiratory problems and intellectual disability, although in some cases no major problems arise.
3. Opercular syndrome
Opercular or perisylvian syndrome in which motor control problems or even paralysis appear in the facial area, is also linked to the Sylvian fissure as there are problems in the opercula, the brain areas that surround the Sylvian fissure and correspond to the not directly visible from the outside.
4. Cerebrovascular disorders
The middle cerebral artery passes through the Sylvian fissure. That is why alterations in this area can also affect this part of the circulatory system, which is capable of generating problems such as aneurysms, hemorrhages or embolisms.
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