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Welcome back to the neuro transmitters, a Clinical Neurology podcast, a show about everything related to neurology. With the goal of reducing your neur a phobia. I'm your host, Dr Michael Ken Trees. And today we're going to be getting back to basics and talk a little bit about some brain stem anatomy, brainstem anatomy can be pretty complicated. But I think it's helpful to develop a framework mentally to categorize the structures there where different problems in different areas can correlate with different symptoms. And I think that helps make it a lot more concrete otherwise it is very abstract. So let's jump right in. So the brain stem essentially is limited above by the thalamus or the thalami bilaterally and below by the spinal cord. And it's responsible for all of the sensory and motor information coming and going to and from the brain as well as control of a lot of the cranial nerves and other functions. So there's three broad areas in the brain stem. Uh at the top most level, there's the midbrain, then the ponds and at the lowest level, the medulla. So within those areas, there are essentially five categories of structures that there's the descending motor corticospinal tracks, the a sending somatosensory pass, that's the dorsal columns and the spine of the lemon tracks. The cranial nerve nuclei, the cerebellar peduncles and the particular activating system and neurotransmitter specific projection pathways of which there are several including the substantia nigra for dopamine, the locus ceruleus for nor epinephrine, the median raffi nuclear for serotonin and the podunk yellow pontine nuclei for acetyl Colin. So we've just gone through quite a few structures already. So let's try and place those in our mental map of the brain stem. So the corticospinal tracks are motor tracks are more along the anterior or ventral side of the brain stem. The somatosensory pathways are mostly posterior dorsal except for in the mid medulla. And then we have the cranial nerve nuclei. One useful way to categorize where the different cranial nerve nuclei are in the brain stem is to just group them up into groups of four. So broadly speaking, in the midbrain, we have one through four in the ponds, five through eight and the medulla nine through 12. Now, there are some exceptions to this. Uh one and 11 don't actually connect to the brain stem and create a nurse. Five and eight. Their nuclei don't really fit nice and neat into one level. And we'll talk about those later on down the line. But broadly speaking, this is a useful mental way to organize where these nuclei are. Now, I'm not planning to go in depth about each cranial nerves function. Today, we'll probably have different episodes devoted to the different nerves or different functions related to those nerves down the road. So this is going to be a little more superficial in terms of function, although we will get to some clinical syndromes near the end. So let's again, now, we have our kind of mental map of where the cranial nerves are located vertically. But let's look at it a little more horizontally. So in the mid brain, you know, cranial nerve three and four nuclei are more medial, moving down to the ponds. Creon under six is more medial fives motor and seven, a little more lateral than that and fives light touch even more lateral. Creator of eight is located more at the Ponta medullary junction on the lateral side. So it's one of those ones we mentioned earlier where it kind of isn't sitting right in the middle of one. And Corey under five actually covers a few different levels as we move on to the medulla. So creator of twelve's nucleuses, midline nine and 10, a little more lateral and then fives pain and temperature sensation even more lateral than that. So let's move on to the cerebellar peduncles. So there are three peat uncles, the inferior which connects the medulla to the cerebellum, the middle, which connects the ponds to the cerebellum and the superior which connects the upper ponds to the cerebellum. It would be logical if it connected to the mid brain. But sadly, things in anatomy are very rarely as logical as we would hope them to be. So, let's move on to the vascular supply. So we've got three main arteries that were usually thinking about for supplying the brainstem. So we have the superior cerebellar artery which supplies the midbrain, the superior midbrain though does get some supply from the post ear, cerebral arteries. There is the anterior inferior cerebellar artery for the ponds primarily and the posterior inferior cerebellar artery for the medulla. So the superior cerebellar artery or SC A and the anterior inferior cerebellar artery or A ICA usually come from the basilar artery, the posterior inferior cerebellar artery or pika usually comes off of the fur to bril artery. Now, all that being said, variations in anatomy are very common and especially as we move upwards from there into the circle of Willis loss of different variations can be seen. So, we've talked about all of these an atomic structures. We have a basic framework, but what is the actual clinical application of this? So I know we're not going to get too much into the carina nerves because that can be a very in depth subject, but let's briefly touch on each of them. So, cranial nerve, one or the olfactory nerve is smell essentially, right. And this is one of the ones that doesn't actually connect to the brain stem. So we'll kind of put that to the side for the moment, cranial nerve to the optic nerves responsible for transmitting visual information into the brain. And it also has a reflex to create a nerve three for controlling pupillary light reaction. Cranial nerve three is in charge of most of the movements of the eye, including the pupillary dilation and contraction. And again, these are all in the midbrain so far, Kroner, four very specific nerve controls just one muscle for eye movement. And I'm going to jump ahead to the ponds. Now because the sixth nerve, the abductions also does one movement. This one's lateral eye movement, it abducts the eye a lot of times you'll see people group 34 and six together just because between the three of them, they cover essentially the majority of the eye movements. Now let's go back a little bit to Korea in er five, the trigeminal nerve, this one covers a lot of territory, does a lot of things. So it does the muscles of mastication or chewing as well as providing sensation to the face. And that sensation has three branches. Hence the trigeminal nerve. Uh we have the ophthalmic maxillary and mandibular branches moving onto cranial nerve seven, the facial nerve. This one provides most of the movements of the face and it also does some special sensations as well. It provides taste to the anterior two thirds of the tongue and also provides a little branch to the Stapedius near the Tympanic membrane to help deaden sounds that are too loud. Cranial eight is the vestibular cochlear nerve. And this, as the name would suggest, provides function from the vestibular system and the cochlear system. So, balance and hearing respectively. So a lot of times these two things do tend to go together if it's affecting the nerve itself, I'm going to group number nine, glossopharyngeal and number 10 Vegas together as between the two of them, they're doing all the laryngeal and pharyngeal muscles. Although the vagus is doing most of the work on that front. The vagus nerve does a multitude of other things that we won't get too into. But just briefly, it helped with vocal cord control covers a lot of autonomic bases for BP and heart rate as well as providing control to some of the thoracic and abdominal viscera cranial nerve. 11, the spinal accessory nerve a little more simple than the last one. It provides control of the sternocleidomastoid and the trapezius muscles. So helping with turning the head and shrugging the shoulders primarily. Last is the hypoglossal nerve number 12, which controls tongue movement. So that's our quick overview of the cranial nerves and their function. Again, we will revisit these in the future. A little more in depth on individual functions and locations depending on the nerve. So how are these signs useful to us and how do they help us localize to the brain stem as we've talked about in previous episodes. One of our main goals in neurological practice is to quote localize the lesion. So we have the timeline and we have the neuro anatomical localization. So one of the key features that makes us think brain stem are crossed signs because the motor pathways cross at the pyramids around the cervical medullary junction and the dorsal columns in the medulla and the spinothalamic tracks in the spinal cord. Most brain stem lesions will cause ipsilateral. That is the same side, bull bar symptoms, but contralateral weakness or numbness in the body. So the face and the body will be on opposite sides. The main exception to this is Creon nerve for the trochlear nerve, which does decussate in the brain stem. So now we have a suspicion that we're in the brain stem. So how about medial versus lateral brain stem syndromes? So, if we think back immediately, we're usually going to have more motor symptoms and we're going to be talking about stroke mostly because that's how a lot of this neuro anatomy was initially characterized. There's a quote a neurology that you learn neuroanatomy stroke by stroke and that's what we're going to be doing today as well. So, medial motor symptoms and that's usually related to occlusion of a penetrating branch of the vertebral basilar system, dorsolaterally are usually more sensory and special sensory symptoms plus or minus cerebellar symptoms and this is usually really to occlusion of one of the more circumferential arteries. So, that would be rscara I CA or are Pika medial medullary syndrome, right. Again, we are medial at this point. So more weakness. So, ipsilateral tongue weakness and contralateral extremity weakness. And this is usually related to an inclusion of the anterior spinal artery. A more famous syndrome is lateral medullary syndrome or Wallenberg syndrome. And this has a plethora of symptoms. So let's go through a few of these. So we have loss of facial and pain, temperature sensation, ipsilateral e do 25 involvement, contralateral pain and temperature loss in the limbs. Vertigo, potentially from the eighth nerve nausea, vomiting and ataxia likely from the cerebellum dysarthria in dysphasia from the nucleus ambiguous to nine and 10 and an ipsilateral Horner syndrome from the descending Oculus sympathetic pathway. And this is usually due to occlusion of the pika. Next, we have top of the basilar syndrome. This can affect the midbrain and one or both of the post your cerebral arteries. A lot of times you'll have vertical gays abnormalities, tosis confusion, uh visual field loss. So it can be a very confusing syndrome when it presents clinically locked in syndrome is another classic one, usually do two basilar artery occlusion and a lot of times these people will be awake and conscious, but they appear comatose because they're paralyzed and all that they may be able to do is have vertical eye movements and blinking. So, in people who have a pontine lesion, it's always important to ask them to try and move their eyes to see if there's any ability to communicate. I have taken care of a couple of patient's with locked in syndrome over the years and it is always a devastating neurologic injury. But it's important that we make sure that these patient's aren't actually comatose because that can certainly change the trajectory and the conversation that we have with them and their family. Lastly, let's talk about a situation where maybe multiple cranial nerves are involved, multiple dysfunctions. So it's good to group these into two categories. Are these nerves all localized together or they more diffuse widespread. So there are different areas where different nerves will cluster together as they travel to and from different parts of the brain and the brain stem. So we're not going to go through all of those. But a few classic ones that I think are important to member are the cavernous sinus because there are so many here. So we have cranial nerves 346, the first branch of five and the second branch of five or V one and V two. So whenever you start seeing, I'm moving to abnormalities, facial sensation, people are abnormalities and there's maybe headache as well. You think maybe like cavernous sinus, thrombosis or other lesions in that area. Another classic one is the internal auditory canal, 7th and 8th nerve go together like peanut butter and jelly here. So a lot of times if you have something like say a vestibular schwannoma, you'll develop hearing loss and facial weakness together. That's the classic presentation. So there are many others that can go together. But I think these two are enough to talk about for the moment. If we're looking at more widespread cranial nerve injuries, then we have to think about more diffuse processes, things like meningitis, inflammatory or autoimmune conditions, neoplastic conditions like carcinoma, this meningitis, Guillain Barre syndrome. And there are of course disorders that can mimic different types of cranial nerve problems. So we think of things like say myasthenia gravis or other neuromuscular junction disorders, which can cause weakness in the bulb our muscles. So that's my wrap up on brain stem anatomy. I hope it's been helpful to you. I know it's a very dense subject, a very daunting subject. And certainly when I was learning neuroanatomy, it was one of those things where you just revisit it over and over again until it hopefully start sticking. My goal is to work our way through the rest of the neuro access. And after we've done kind of a broad overview of each area coming back, more detailed on different specific areas that it get a little more in depth on different functions, more specific neurologic syndromes, uh more pathologic states and so forth. So if you enjoy this podcast, please leave a five star review on Apple Spotify or wherever you get your podcasts. This really helps with getting the show noticed and please do make sure to subscribe for future episodes. You can find me on Twitter at Doctor Ken Trees. That's Drkentris or by email at the Neuro transmitters podcast at gmail dot com and feel free to send me any of your questions or show suggestions. I'll see you next time.