Hello everyone! It's Megan from Kenhub here, and welcome to our tutorial about the ventricles of the brain. Before we start talking about the ventricles of the brain, let's first define the word ventricle. A ventricle is a hollow area or cavity within an organ usually filled with some kind of fluid. Our brain has four interconnected ventricles and the fluid that fills them is called cerebrospinal fluid. Cerebrospinal fluid is a clear fluid that has several important functions in our central nervous system and you might be wondering where this fluid comes from. Well, almost every part of the ventricular system that we're going to see in this tutorial contains a choroid plexus which includes epithelial cells that produce the cerebrospinal fluid. So as I just mentioned there are four ventricles within the brain – two lateral ventricles (the left and right lateral ventricles), the third ventricle found near the central of the brain, and the fourth ventricle located deep to the cerebellum.
Before we go any further, let's orientate ourselves. The image you can see on the right will feature throughout this tutorial so it's important to understand what exactly we're looking at. Basically what we have here is a site on view of the ventricles of the brain which are colored blue with the otherwise surrounding cerebrum removed so we can see structures such as the cerebellum, the brainstem and the start of the spinal cord. So let's begin with the two largest ventricles which are the lateral ventricles.
There is a lateral ventricle in each hemisphere of the brain and therefore there's a left lateral ventricle and a right lateral ventricle, each found in the respective side of the brain. Here we can see the right lateral ventricle hiding behind the left lateral ventricle as we're viewing these structures from the left hand side.
So now let's have a closer look at these ventricles. Both lateral ventricles are roughly C-shaped. They have a central body and three horns projecting into the lobes of the brain namely the anterior horn, the posterior horn and the inferior horn. The area we can now see highlighted in green is the central part of the lateral ventricle which is located in the region of the parietal lobe. Its roof is formed by the corpus callosum and it's floored by the superior surface of the thalamus and the tail of the caudate nucleus. Now you may have noticed that our image has changed slightly so let's familiarize ourselves with it.
We're still viewing the ventricles from the left hand side of the body, however, we can now see the surrounding cerebrum. Let's move on to the three horns of the lateral ventricle starting with the one we can see here which is the anterior horn. The anterior horn of the lateral ventricle is essentially an extension of the lateral ventricle into the frontal lobe which is why it's also known as the frontal horn. The frontal horns of each lateral ventricle are separated medially from each other by the septum pellucidum. The roof of these horns is formed by the corpus callosum while the floor is formed by the head of the caudate nucleus.
Next, we'll take a look at the inferior horn of the lateral ventricle which extends into the temporal lobe and is therefore also referred to as the temporal horn. It contains part of the limbic system and is adjacent to the caudate nucleus. The floor of the inferior horn is formed partially by the hippocampus. Moving posteriorly, we can see the posterior horn of the lateral ventricle highlighted in green. It extends variably as a fingerlike projection into the occipital lobe which is why it's also known as the occipital horn. Its floor contains the calcar avis and the collateral trigone. The collateral trigone is this flat and triangular area located at the transition between the inferior horn and the posterior horn of the lateral ventricle.
Now that we've discussed the central part and the three horns of the two lateral ventricles, we'll look at this small channel located at the floor of the anterior horn. This channel is called the interventricular foramen and links the lateral ventricles with the third ventricle at the midline of the brain. The interventricular foramen is also well known as the foramen of Monro.
In terms of location, the third ventricle is located in the diencephalon of the brain. It’s a narrow slit that's bordered laterally by the medial nuclei of each thalamus and the hypothalamus. Superior to this ventricle are the fornix and the corpus callosum. Anteriorly, the space is limited by the lamina terminalis and the anterior commissure. The floor of the third ventricle is formed partially by the infundibulum which attaches to the pituitary gland. And finally the posterior wall is attached to the pineal wall. The cavity of the third ventricle is marked by a number of elongations and recesses. All of its recesses are named according to their related structures. So inferiorly the third ventricle continues as the infundibular recess which extends into the infundibulum and we can see this recess here highlighted in green.
Superior to the infundibular recess, we have the supraoptic recess. As you may have deduced from the name, this recess is located here above the optic chiasma. If we move posteriorly and zoom in slightly, we can see the pineal recess of the third ventricle which lies between the superior and inferior laminae of the stalk of the pineal body. Superior to the pineal recess and the pineal body is the final recess of the third ventricle – the suprapineal recess which we can see here highlighted in green.
If we look immediately below the pineal recess, we see this then anatomical structure stemming from the floor of the third ventricle which is called the cerebral aqueduct. This structure connects the third and fourth ventricles and is also well known as the aqueduct of Sylvius. The cerebral aqueduct is very important for the flow of cerebrospinal fluid. As we’ve already mentioned, most parts of the ventricular system contain clusters of choroid plexus however the aqueduct of Sylvius is the only major part of the ventricular system that doesn’t contain a choroid plexus.
Towards the end of the cerebral aqueduct, we can see the last ventricle of the brain which is the fourth ventricle. This ventricle lies behind the pons and medulla and in front of the cerebellum. The fourth ventricle extends from the cerebral aqueduct to the obex which is this point here where it narrows to become the central canal of the spinal cord. The fourth ventricle has a characteristic diamond shape and for this reason its anterior floor is named the rhomboid fossa and the posterior roof is named the tent-shaped roof.
Cerebrospinal fluid that is produced or flowing in the fourth ventricle can exit to the subarachnoid space near the lateral apertures and a single median aperture within the roof of the fourth ventricle. The cavity of the fourth ventricle has several extensions, the largest being the two lateral recesses located on either side of the midline. Here we can see the left lateral recess highlighted in green. These recesses extend laterally between the inferior cerebellar peduncle and the peduncle of the flocculus of the cerebellum. The lateral recesses are of great importance because they open to the subarachnoid space as the lateral apertures of the fourth ventricle also known as the foramina of Luschka. As we've already mentioned, the fourth ventricle of the brain extends inferiorly as the central canal of the spinal cord. This structure runs the entire length of the spinal cord and contains cerebrospinal fluid.
Now that we have an understanding of the ventricles of the brain, let's go over some clinical notes related to this ventricular system and the cerebrospinal fluid that fills it. Hydrocephalus is one of the well-known clinical conditions associated with ventricular system malformations and can be diagnosed using computerized tomography or ventriculography. This condition is characterized by an abnormal accumulation of cerebrospinal fluid within the brain due to a disturbance in its flow or due to a decrease in its absorption. This leads to an increased volume of cerebrospinal fluid in the ventricular system and therefore an increased intracranial pressure. During childhood, this condition can cause progressive enlargement of the head potentially causing convulsion, tunnel vision, slowing of mental capacity, cognitive deterioration, headaches, vomiting, blurred vision, difficulty in walking, drowsiness and several other symptoms. It's therefore important to recognize the signs of hydrocephalus and to also be able to identify possible causes in order to confront and treat this condition.
Before we conclude our tutorial, let us briefly summarize what we've discussed today. So we established that there are four ventricles in the brain. First, we had the two lateral ventricles each made up of a central part and three horns – the anterior horn, the posterior horn and the inferior horn. We then saw that these ventricles communicate with the third ventricle via this structure here which is called the interventricular foramen. Next, we talked about the third ventricle and its four recesses – the infundibular recess, the supraoptic recess, the pineal recess and the suprapineal recess. We also saw that the cerebral aqueduct here links the third and fourth ventricles. Finally, we discussed the fourth ventricle which is continuous with the central canal with the spinal cord.
So that brings us to the end of our tutorial about the ventricles of the brain. I hope you enjoyed it and thank you for listening.
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Now, good luck everyone, and I will see you next time.