Brainstem Anatomy 2 PDF

[00:00:05] >> We talked about the layout of the brainstem with respects to the midbrain, pons, and medulla. There are certain components of the brainstem that actually span all three sections. So in your textbook, you'll see a feature called the reticular formation, and the reticular formation is ju...

[00:00:05] >> We talked about the layout of the brainstem with respects to the midbrain, pons, and medulla. There are certain components of the brainstem that actually span all three sections. So in your textbook, you'll see a feature called the reticular formation, and the reticular formation is just a general loose aggregate of cells that actually lack a precise anatomical boundary. [00:00:34] However, these cells play essential roles in maintaining a Various bodily functions and influencing higher level brain processes. So these cells, like we said, span all three sections and go from the brain stem all the way up to the thalamus, and then eventually, once it gets to the thalamus, will influence various aspects of the cortex. [00:00:59] So in thinking about the reticular formation, the basic structure is kind of listed here. And what you'll notice is I've laid it out in terms of just the various nuclei that are involved in the reticular formation. And then I have another aspect called the reticular activating system. So what you'll notice over here on the right-hand side are various nuclei within the reticular activating system. [00:01:24] And these reticular nuclei help regulate neuronal activity throughout the central nervous system. Each of these nuclei produce a specific neurotransmitter. These neurotransmitters have a huge influence on other parts of the brainstem as well as the cerebrum and cerebellum. So I have listed just the first two are kind of in the more dark black fashion and the raphe nuclei is really important in producing serotonin. [00:01:57] And then the locus coeruleus and the medial reticular area are really important for producing norepinephrine. The other ones listed that are grayed out, I'm not necessarily concerned that you are aware of, but the ascending reticular activating system is a unique feature within the reticular formation that is helpful for generating what we call conscious levels of awareness of not only yourself and your surrounding. [00:02:31] So this feature is kind of helps govern your alertness, your sleep, your attention. And if damaged, you can make the assumption that individuals may have different levels of consciousness. While we discussed the basic layout of these loose aggregate of cells of the reticular formation, it's important to consider just the overall purpose of these cells. [00:02:59] And this is definitely not an exhaustive list, but just a couple main ones I want you to think about. So the reticular formation is really crucial in integrating different sensory information from all different parts of the nervous system. And not necessarily specific to localizing a specific type of sensory information, but just more in that kind of general awareness category. [00:03:25] It will also help regulate different motor, autonomic and levels of consciousness. And the way I like to remember this portion is, let's say, the metaphor I like to use is If you are a sprinter getting into the starting blocks, and there's that moment where the starter says, on your marks, get set. [00:03:50] And in that brief pause, your central nervous system is getting flooded with a lot of different endorphins because you're ready to explode out of the blocks, there's a lot of reflex activity that happens. Your body is getting primed, your heart rate starts to increase a little bit, your autonomic nervous system starts to kick in. [00:04:08] And so in that brief pause, your reticular formation is kind of lighting up on fire in order for you to explode out of the blocks and hopefully win the race. The third purpose is to modulate pain information or nociceptive information. And then there is some evidence to support that the reticular formation is important in locomotion. [00:04:37] However, this hasn't necessarily fully been vetted at this time. One key function of the brainstem is the intimate relationship it has with our cranial nerves, and more specifically, the housing of certain cranial nerve nuclei. Now, if you remember, a nuclei or a nucleotide or a nucleus kind of serves as the control center for a specific nerve or neuron. [00:05:06] Now what I have pictured here on the right hand side is a very complex picture that I don't expect you to know all the intimate details. But what I wanted to show you here is just in general how these nuclei are laid out. And so if you look at it here, if a cranial nerve nuclei contains something related to more autonomic or motor function, it generally lies a little bit more medially within the brainstem. [00:05:36] Versus if a nuclei contains something more sensory related, that tends to lie a little bit more laterally within the brain stem itself. And this layout is actually related from the embryological development that we've discussed before. So what this slide is meant to show you, it's just more of an FYI on how the layout of those cranial nerve actually come to take place. [00:06:11] So if you consider here, this is that embryological development where the neural canal takes place, right? And then you have those somites that then start to branch off into sensory and motor functions. But within the brainstem itself, what actually starts to happen is as the brainstem starts to kind of reform and reshape, it kind of opens up like a little bit of a flower. [00:06:42] So if you want to think about it, if you were to cup your hands around the neural canal here. Then you just open it up like a flower, what you'll see here is a lot of the sensory tracts are located here on the outside or the more lateral portions, and a lot of the motor and autonomic functions are located here a little bit more painterly. [00:07:07] I'm not expecting you to memorize this, but just if you're kind of scratching your head going, well, why are the sensory tracts lateral and why are they medial? It all stems from the embryological events that take place. Now this wouldn't be a neuroscience lecture without discussing blood supply to certain structures. [00:07:30] So in thinking about the blood supply to the brain stem, it's important to consider or remember which specific arteries actually help provide blood to those structures. So what I have here is I highlighted or put a star next to, I should say, the major arteries that are at play. [00:07:51] So we have the anterior spinal artery, we have the pontine artery, the posterior cerebral artery, as well as the posterior communicating artery. So, if you think about it, the vertebral branches, the anterior and posterior spinal arteries, actually help supply a lot of blood to the medulla. The basilar artery and its branches, specifically those pontine arteries, really help supply a lot of blood to the pons itself. [00:08:28] And then the midbrain gets a lot of its blood supply from the posterior cerebral artery as well as the posterior communicating artery. Now, the reason why this is important is that alot of brainstem lesions or issues will be vascular in nature, and so a lot of what you'll start to notice if there's an insult to the brainstem will happen fairly quickly, which is kind of neurology 101. [00:08:54] If it happens quickly, it's probably a vascular issue compared to something a little bit slower of an onset, like a tumor or some other degenerative disease. Injuries to the brainstem can vary in their presentation, but for majority of individuals who have an injury to the brainstem, it can lead to just varying levels of consciousness, or what we in the medical community refer to as disorders of consciousness. [00:09:26] So there are three different levels of disorders of consciousness listed here on the slide, going from the most severe, which is a coma, to the least severe, which is a minimally conscious state. I don't expect you to know all the intricate details as this is more beyond the scope of this course and that you'll discuss more in your neuromuscular practice. [00:09:48] But what I wanted to highlight was a fairly well known case that happened in the early 2000s, involving an insult to the brainstem that led an individual to be in a vegitative state. And the individual is depicted here and her name was Terri Schivo. Now, the details of the case can be readily found on the Internet. [00:10:10] So if you're curious, please do look her up. But what I wanted to highlight is just the complexities of the brain stem. And even still to this day, there is a lack of agreement or some discrepancy on the functions of the brainstem and what it will present like clinically. [00:10:29] And more specifically, what is a voluntary action of the brainstem and what is involuntary that the brainstem contributes to? So I won't necessarily ruin the details, but what I wanted to share with you is that injuries to the structure have been necessarily featured on the news. Unfortunately, the prognosis for Terry wasn't that great, which I think speaks to just the importance of the structure and what it can do in terms of maintaining someone's life functions.