In the next couple of minutes, I will be talking to you about the general anatomy of the human brain, or more specifically, of the cerebrum, which is the part of the brain that we are mostly concerned with during awake surgery. The cerebrum consists of two hemispheres that are interconnected. The most important and largest of these connections is the corpus callosum. The cerebrum can, by and large, be divided into superficial cerebral cortex and a subcortical white matter underneath. When performing a craniotomy after opening the dura mater, which is the first layer of the membranes that surround the brain, the first thing we see is a the cerebrum’s cortical surface.
The cerebrum is folded into itself, which results in a much larger cortical surface than the outer cerebral surface area. Through this folding, cortical banks are created called gyri that are separated by larger and smaller grooves, which are called fissures and sulci. Some of these can be used to delineate the five or six lobes that the cerebral hemisphere can be divided into. Of course, during language testing and awake surgery, only a limited area of the cortical surface is exposed, in most cases, only a part of the lateral surface of the cerebrum. Most importantly, within this area, the Sylvian fissure and the central sulcus should be recognised. The Sylvian fissure separates the frontal lobe from the temporal lobe.
And the central sulcus separates the frontal lobe from the parietal lobe. Besides these three lobes, frontal, temporal, and parietal, there are two or three other lobes– the occipital lobe, the insula, and some distinguish a sixth lobe, the limbic lobe located on the inner surface of the cerebral hemisphere. We navigate around the cortex of each lobe by dividing the lobes even further into individual gyri and sulci. The uppermost gyrus in the frontal and temporal lobe are called superior. The ones in the middle, hence, are called middle gyri. And the lower ones are called inferior. For instance, these are the superior temporal gyrus, the middle temporal gyrus, and the inferior temporal gyrus.
If you need to point out a specific part of the gyrus, you use the terms anterior in the front and posterior in the back. So this part of the superior temporal gyrus is therefore the anterior superior temporal gyrus. In addition, the frontal lobe holds the precentral gyrus. The parietal lobe can be divided into the superior and inferior parietal lobule, as well as the postcentral gyrus. And the inferior parietal lobule, just behind a temporal lobe, the supramarginal gyrus and the angular gyrus are located. The most important functional areas is on the lateral surface of the cerebrum that should be considered are, first, the primary motor cortex, second, the primary sensory cortex, third, Broca’s area, and forth, Wernicke’s area.
The primary motor cortex is located in the precentral gyrus. The primary sensory cortex is located in the postcentral gyrus. Broca’s area is generally thought to be located in the posterior part of the inferior frontal gyrus. The inferior frontal gyrus is divided in an orbital, a triangular, and an opercular part. The latter two should be in the location of Broca’s area. Wernicke’s area is thought to reside in the posterior part of the superior temporal lobe. It must be noted that of these language areas, there’s a lot of variation in the exact location as shown by language testing during awake surgery.
Although there are some areas, such as these mentioned just now, that seem to be involved with one particular function, the brain is thought to function as a very complex network in which the various cortical areas are interconnected. The anatomical substrate of the connections is a subcortical white matter which connects adjacent cortical areas but also areas from different lobes and even areas in the two different hemispheres. Within this white matter, several tracts are distinguished that connect distance cortical areas. The arcuate fasciculus and the inferior frontal occipital fasciculus are of particular importance in language testing. These tracts connect the frontal and temporal parietal language areas. You have now got a glimpse of how complex the brain is.
In the following steps, we will help you practise the most crucial terms for the course once more.