Brainstem 1 PDF

[00:00:00] [MUSIC] [00:00:12] So today's outline looking at the brainstem is listed here on the left hand side. I'd like to draw your attention to the picture on the right hand side, as it will serve as our metaphor for the brainstem. In thinking about the brainstem, I like to think of it and its f...

[00:00:00] [MUSIC] [00:00:12] So today's outline looking at the brainstem is listed here on the left hand side. I'd like to draw your attention to the picture on the right hand side, as it will serve as our metaphor for the brainstem. In thinking about the brainstem, I like to think of it and its functions as the main character of a production. [00:00:33] And in the case of west side Story, the main character, his name is Tony. And Tony, just like the brainstem, serves many vital functions throughout the show, or the play or the movie. And without the main character, the show can't go on. And that's how the brainstem functions as well. [00:00:51] Here are the objectives for the brainstem lectures. You'll see them listed here on the slide as a reminder, these objectives will be very helpful for you to serve as a study guide for future exams. I wanted to begin the journey through the brainstem with just a brief general overview. [00:01:11] Now, in thinking about the brainstem from an evolution perspective, it technically is the oldest part of the brain, and it shares actually a lot of similar functions to certain reptiles, fish, etc. So what you'll see here is a picture of the brainstem on the right hand side and its components. [00:01:30] But what I want you to be mindful of is that while we'll discuss each of the three components of the brainstem in isolation, try to think about it as these three structures work together in tandem or as a team in order to achieve vital functions for living. So with respects to key functions of the brainstem, while there are many, there's just a couple big ticket items I want you to be mindful of. [00:01:57] The brainstem as a whole helps serves critical roles in cardiovascular and respiratory function. It helps regulate your sleep, it provides motor and sensory function for the head of the neck. And a way to think about it is since the brainstem is a continuation of the spinal cord, we know the spinal cord provides motor and sensory for the body. [00:02:21] The brainstem is just kind of a addition to motor and sensory for the head and the neck. Unfortunately speaking, because there's so many critical functions of the brainstem, when there is an injury to it, it can lead to a lot of damage and even death in some individuals. [00:02:39] And there are certain nerves, what we call cranial nerves, that attach to the brainstem. And if you can start to remember the brain stem and the cranial nerves, it really helps you just remember the overall functions. When looking at the actual structural relationship, we'll kind of walk through the slide here. [00:02:58] Just rostral to the brainstem is a structure called the thalamus. Posterior to the brainstem, you can't see it here, but if you go to this part, you can, is the cerebellum. Just caudal or towards the tail end of the brainstem will be the spinal cord, which you can see right here. [00:03:17] And then an anterior to the brainstem, you can't necessarily see it with this picture, but it is the base of the skull and the sphenoid bone. What I wanted to highlight here in this picture as it rotates, is just the location of the brainstem as it relates to other structures. [00:03:37] So the brainstem in this video is kind of that deeper, pinkish reddish color, and you can kind of see the arrow pointing to it as well. As you can see with this video, the brainstem is kind of like the tree trunk as it relates to all the other structures within your cranium. [00:04:02] So in starting our journey through the brainstem, we'll start with the most superior or rostral component, which is a structure called the midbrain. What you'll see is the midbrain is highlighted here in purple, okay? And structurally speaking, just rostral or superior is the diencephalon, which is the thalamus and hypothalamus. [00:04:23] And then just inferior to the midbrain is the pons. Now, within the actual midbrain itself, you can't see here on this picture, there's a tiny little hole or canal that's called the cerebral aqueduct, which serves as this transition period between the third and the fourth ventricle. The biggest structural relationship I want you to be mindful of is this feature here called the crus cerebri. [00:04:50] And it's essentially a continuation of a structure called the corticospinal tract, which is a major pathway from the brain to your muscles on how we actually move our body. The other three here, the bacillus pendiculae, the tegmentum and the tectum are more just for your FYI, okay? If you wanna look more into them, you can. [00:05:14] The major features of these three structures is it's really involved with cranial nerve function and eye movement that kinda serves the purpose here. Cranial nerves 3 and 4 are major features within the midbrain. And you can see that here, the picture on the right hand side, the third cranial nerve is called the oculomotor nerve, and its nuclei sits here in the midbrain. [00:05:39] And the fourth cranial nerve, also known as the trochlear nerve, its nucleus sits right here in the midbrain as well. Shown here in this slide is what we call an axial cut or a cut through the midbrain. And what I wanted you to appreciate here is just a few specific structures. [00:05:59] You'll see this big red dot. This is called a red nucleus. And it's a feature of the midbrain that's believed to help facilitate motor coordination and control, especially with walking. The little hole here that we talked about, that's the cerebral aqueduct, and it's what helps connect the third and the fourth ventricle. [00:06:20] And it's a hallmark feature of the midbrain. And so if a pathologist or neurologist is looking at an image and they see this little hole, they will know that they're in the midbrain. So it's an important feature. And then what you'll notice here in this kind of grayish tint is a feature called the substantia nigra. [00:06:39] And this is actually where a lot of dopamine is produced, which is a chemical that helps influence movement. You may be familiar with a pathology called Parkinson's disease, where the substantia nigra starts to lose a lot of dopamine within that system. Now, the midbrain is a very important structure, specifically when it gets damaged. [00:07:04] And there's two very classically defined postures an individual may adopt when there is damage to the midbrain and are shown here on the right hand side. The first one is what's called a decorticate posturing, where essentially the arms are flexed towards the core, the feet are more extended, and that's how I remember decorticate posturing as you're hugging your arms into the core of your body. [00:07:30] The other posture is called discerebrate posturing, where essentially all the limbs are in an extended position. Basically, decorticate posturing is an injury that's more rostral in the midbrain or more superior than diserebrate posturing. And you will likely see this injury in individuals who have had a severe traumatic brain injury. [00:07:56] Unfortunately, these posturings aren't necessarily well understood. However, functionally they both have equally as bad of a prognosis. And so a lot of times, if an individual is adopting this posture, you can be under the assumption that they may have had a brainstem, specifically midbrain injury. The next structure within the brainstem, if we go a little more caudal, is a structure called the pons. [00:08:23] And embryologically, the pons was derived from that bend in the hindbrain that you remember from the embryological lecture. And what you can see here is that's the big structure relationship that links the pons and that cerebellum together. And this is a picture shows a really nice connection there. [00:08:42] We look just rosterly or superiorly, we have the midbrain. And then just inferior is the medulla. A couple key structures here, there's a lot of vertical tracts that we'll discuss in a future lecture. But the main feature of the pons is it serves to house the nuclei of cranial nerves V, VI, VII, and VIII. [00:09:10] The most inferior or caudal structure within the brainstem is referred to as the medulla oblongata, or most people typically know it as medulla for short. I always joke with the medulla oblongata as it was made famous in a quote from the movie Waterboy from Adam Sandler. Structurally speaking, if you look here on the right hand side, the medulla, just superior is the pons, and then inferior is the spinal cord. [00:09:41] Some key structures similar to the pons. It houses a lot of cranial nerve nuclei, specifically cranial nerves IX, X, XI, and XII. And then right in between the pons and medulla, you can find the nuclei for cranial nerves V and VII as well. Now, the big feature of the medulla here is highlighted by what I'm saying is vertical tracks. [00:10:13] And what I mean by that is there are structures similar to wiring, like you would wire a TV to the wall that come from the brain and run through the brainstem that help control things like movement and sensory function. But there's a unique feature that happens with those tracks. [00:10:34] They end up crossing, or what we call decussating. And that happens here in the medulla. So that's a really key feature. The medulla is this kind of place, like Grand Central Station, where a lot of things cross with respects to movement and sensation. Another key feature of the medulla is it houses the olivary nuclei, which aids in cerebellar function and perception of sound. [00:11:02] Like we discussed, cranial nerves, the main ones I want you to remember are cranial nerves IX, X, XI, and XII. Now, the slide is a little bit busy, but what I want you to appreciate is the different tracts that are responsible for movement and sensation. And if you were to look here in the left hand side, this is how, if you're going to move a muscle, your brain would send a signal down from one side of the brain. [00:11:32] And then right where you see this cross is what we call decussating or crossing to the opposite side. And that's what we traditionally know. The right side of the brain controls the left side of the body and vice versa. So this picture does a nice job of showing that cross here in the medulla. [00:11:53] So for movement, that's through the corticospinal tract. And then sensory wise, what you'll see here is as sensory information, such as touch comes into your body, it will still cross or decussate at the medulla and travel to the opposite side. So the medulla kind of serves as that pivot point, if you will, to relay information to and from the brain and the body.