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Deep nuclei of the cerebellum
Hey everyone! It’s Nicole from Kenhub, and welcome to our tutorial on the cerebellar nuclei. So, today we're going to be exploring the nuclei that are found within the cerebellum and the structure that we see here on the back of the brainstem. So, first off what we're going to do is a quick review of what the cerebellum is, looking at the following gross structures – the vermis, the various fissures and zones, the fourth ventricle, the superior medullary velum, the superior cerebellar peduncles, the medial longitudinal fasciculus, and, lastly, the lingula. We will then review some of the nuclei that we find deep in the cerebellum, and these include the fastigial nucleus, the interposed nuclei, and the dentate nucleus.
The cerebellum is an incredibly important structure that consistently is monitoring adjusting and aiding in our motor control, gait, and movement coordination. The cerebellum is found at the base of the brain inferior to the cerebrum and just posterior to the brainstem, and we can see it here highlighted in green. If we look at it from a different angle just here, we can see deep inside some various structures within it and these structures are going to be the ones that we'll discuss in detail and we'll review their functions.
So, firstly, let's take a look at the cerebellum as a whole. So this image shows us the superior or tentorial surface of the cerebellum and it's quite easy to see here that the cerebellum has two hemispheres – the left hemisphere and the right hemisphere. Separating these two hemispheres and running right down the center is a structure we call the vermis.
The vermis begins here at the anterior cerebellar notch and curves one hundred and eighty degrees to the posterior cerebellar notch located here. The vermis is further divided into the superior and inferior vermis, and the superior vermis we can see from the tentorial view and it's pointed out over here. If we take a look at an inferior view of the cerebellum, we can now see the inferior vermis pointed out here and we can also see the most anterior portions of the superior vermis as well.
So have a look at this image over here. Highlighted on the cerebellum is the horizontal fissure and, if we cut the cerebellum along the horizontal fissure and then lay it face up, we end up with a structure that looks like this. So we can still see the vermis in this structure highlighted in green and the structure actually allows us to break the cerebellum into several zones that will help us localize particular cerebellar nuclei.
So, first, we have the vermal zone highlighted here in green and, just beside this zone both on the left and right side, we have the paravermal zones highlighted in blue. And, lastly, adjacent and on the outermost edges, we have the lateral zones highlighted in red.
So a very important cavity that is associated with the cerebellum is the fourth ventricle, and it's very important to note here that our brain has four ventricles that are in communication with one another and they’re filled with cerebrospinal fluid, which is a clear fluid that has several important functions in our central nervous system.
The ventricles of our brain are four. So as we mentioned, we had four ventricles in our brain – the two lateral ventricles as well as the third and the fourth ventricle. The fourth ventricle is closely associated anatomically with the cerebellum, and in this image, we can see the entirety of the ventricular system traveling from the cerebrum down to the spinal cord, and the fourth ventricle highlighted here in green is sandwiched between the cerebellum and the brainstem. So when we take a look at the image in cross-section, we can see the fourth ventricle as the smaller cavity anterior to the cerebellar structures.
The roof of the fourth ventricle is made up of two structures, one of which is the superior medullary velum and the other structures that make up the roof are the superior cerebellar peduncles which we'll discuss later in this tutorial. And as we can see here on the image, the superior medullary velum highlighted in green is made up of a thin sheet of white matter, and if we take a look at a different angle, we can see in this horizontal section of the cerebellum that the superior medullary velum can be seen at the posterior surface of the fourth ventricle as it descends downwards.
So closely associated with the superior medullary velum is the lingula of the cerebellum, and the lingula highlighted in green in this image is found atop the superior medullary velum. And, technically, the lingula is the most anterior end-piece of the superior vermis and is made up of a few cerebellar folds.
So now that we've reviewed the zones of the cerebellum and had a look at the fourth ventricle, we can use these as landmarks in determining the cerebellar nuclei that we are looking at. So please remember that cerebellar nuclei are paired and are found in both cerebellar hemispheres. So first let's start with the most medial pair of nuclei – the fastigial nuclei.
So the fastigial nuclei are found within the vermal zone of the anterior of the cerebellum. They are the most central pair of nuclei and can be seen highlighted in green just here just posterior to the fourth ventricle and its superior medullary velum, and the fastigial nucleus is involved in the maintenance of balance and it receives afferents from the vermis and sends efferent projections to the spinal cord and ventral lateral thalamic nuclei, and this in turn results in the stimulation of proximal and trunk musculature to maintain balance.
As we move out laterally, we move into the paravermal zone. And within the paravermal zone, we find the interposed nucleus, and the interposed nuclei are actually composed of two separately named nuclei – the globose nuclei and the emboliform nuclei, and we can see here that the globus nuclei are the more medial set of nuclei within the structure while the emboliform nuclei are the more lateral set within this structure.
So together the globus and the emboliform nuclei function together to receive proprioceptive impulses which then relay these impulses to other structures found within the brainstem and the thalamus. Projections eventually make their way to the spinal cord where they act on distal musculature like our arms and our legs and they act to regulate skilled muscle tone and flexor motor activity of the distal musculature on the ipsilateral side.
So the last set of nuclei that we're going to be looking at are the dentate nuclei and these nuclei are found within the lateral zones of the cerebellum and they resemble crinkled paper bags with its opening facing anteromedially. So, the dentate nuclei are the largest of the cerebellar nuclei and, unlike the others, the dentate nuclei actually enclose various white matter fibers that come in to its opening. Its primary function is to aid in the regulation of many aspects of voluntary motor activity and these include inception, planning, and timing of motor activities.
So coming into and out of the cerebellum are large bundles of white matter fibers that carry information into and out of the structure to other important areas of the central nervous system. The first of which we’ll look at are the large superior cerebellar peduncles.
So, the superior cerebellar peduncles are where the major tracts join the cerebellum and the thalamus and the cerebellum and the red nucleus pass through. There are, of course, several other white matter tracts that pass through the structure, all of which are involved with coordination, balance, motor control, and movements of the eyes to various stimuli. So let's take a different look at the superior cerebellar peduncles in this image.
So looking at this horizontal section that we've been focusing on throughout this tutorial, it's easy to see that various white matter fibers travel into and out of the cerebellum through this structure, and this image especially highlights the superior cerebellar peduncles that are captured by the dentate nucleus.
At the most anterior portion of this section of the cerebellum, we find the decussation of the superior cerebellar peduncle. So, remember whenever we're talking about something decussating that this means that there are fibers that cross over to the opposite or contralateral side from which they started. So, some fibers will cross at this decussation so they synapse on the higher-order structures on the opposite side of the midbrain or the thalamus or the cerebrum. So if something originates on the left side of the cerebellum and sends white matter fibers through this decussation point, they could synapse on structures on the right side of the midbrain or the thalamus or the cerebrum.
The last white matter bundle tonight is the medial longitudinal fasciculus highlighted in green and found just posterior to the decussation of the superior cerebellar peduncle and anterior to the fourth ventricle. The medial longitudinal fasciculus receives and integrates information from the cranial nerves responsible for eye movement and sensation along with information from the vestibulocochlear nerve and integrates this information to help regulate eye movements.
So now let's discuss an important clinical aspect of the cerebellum and the structures associated with it.
So if we look back at this image of the fourth ventricle and zoom in, we can see these two structures that branch off of the fourth ventricle – the foramen of Luschka and the foramen of Magendie. The foramen of Luschka also exists on the other side of the fourth ventricle and so we call them the foramina of Luschka. So an easy way to remember where we find these foramina in the fourth ventricle is that Luschka begins with the letter L and they’re found laterally while the foramen of Magendie begins with an M and we find it medially.
So you may be asking yourself, why are these structures important. Well, they're the final structures cerebrospinal fluid drains through to end up in the subarachnoid space to be recycled back into the circulation. So if tumors arise in this area called posterior fossa tumors, they can block drainage of fluid and cause it to back up and this eventually causes hydrocephalus or a build up of fluid in the ventricular system and results in the swelling of the brain, and as you can imagine, hydrocephalus can cause a whole array of symptoms and tumors in this particular area will cause symptoms that impair the functions served by the cerebellum like an impaired ability to walk or problems with balance.
So this brings us to the end of our tutorial on the cerebellar nuclei. Today, we looked at several gross structures of the cerebellum and its nuclei and two white matter bundles that are associated with it. First, we looked at the gross structures – the vermis, the lingula of the cerebellum, the fourth ventricle, and the closely related superior medullary vellum. From there, we looked at the four main cerebellar nuclei that are found paired on each half of the cerebellum, and we found the most medial to be the fastigial nuclei, the globose nuclei, the emboliform nuclei, and, lastly, the dentate nuclei.
Lastly, we covered the major white matter bundles we see carrying information into and out of the cerebellum. So we found the superior cerebellar peduncles and the decussation of the superior cerebellar peduncle – the most anterior in this image – and then we quickly discussed the medial longitudinal fasciculus which is just posterior to the decussation.
To round off the tutorial, we discussed posterior fossa tumors and their potential to cause hydrocephalus through blockage of cerebrospinal fluid out of the fourth ventricle and their potential to cause hydrocephalus through blockage of cerebrospinal fluid out of the fourth ventricle.
So this concludes our tutorial on cerebellar nuclei. Thanks for following along with me and we'll see you next time!