DIP Episode 371 - The Spinal Cord (for Step 1-3)

Okay, welcome. My name is Divine. This is episode 371 of the Divine intervention podcast. And in today's podcast, we're going to be talking about the spinal cord. I'm going to be reviewing the spinal cord for all the USML exams, step one, step just against step three. Today for the most part, I just want to orient you to the spinal cord. The neurologist is just one of these things that many people give up on. They're like, this thing is way too hard to learn. I'm not going to always brain cells learning this. But the thing is, most times, because it's something people just ignore, most times they make the questions pretty easy on the exams. So if you're just putting a little extra effort, you could get all those questions. The thing is, again, it may be five, six questions that ends up differentiating between pressing getting the 240s versus getting the 250s. So it might as well just snuggle the points that you can get. If you're getting many of those questions that many people are getting wrong, and that's certainly going to help your score in the long run. And again, if you're taking the USML step two, see here, step three exams. Any time within the next four weeks, I would encourage you to attend the NV Me Testic and Strategist course that we have next Monday from 2 to 4 30 p.m. mountain time. That's 4 to 6 30 Easter. And during the course, we address many things. We address how to read questions. When you narrow down your answer choices to two things.

Which one do you pick from those two? How do you answer ethics questions? How do you answer risk factor questions? How do you answer questions when you don't know what in the world you're talking about? We talk about all those things. And we also talk about strategies for just eliminating answers that make absolutely no sense. But again, these are, because again, you can know, but you also need to be able to pick out the right answer. So we work on picking out the right answer in that course. Again, tons of people have taken this course. They've done extremely well. And then, I've had many people have really good score increases from that course. And then we have the 24 hour course. It's going to be taking place from 22nd to 25th of February. That's going to be from 7 a.m. to 1 p.m. mountain time each day. That's going to be from 9 a.m. to 3 p.m. Easter time. Right? And again, if you're, you know, we review P. Surgery, I.m. OB-Guine, Psychneural, Surgery, Bio-statistics, Ethics, Communications, Multisystem Persists, and Disorders. Healthcare Systems. Right? So again, maybe you will have taken these courses and did it on really well. To be honest, review probably one of my most favorite days during the week is Wednesday. Because I pretty much always get good news on Wednesdays from multiple people. Okay. So let's go ahead and jump right into it. Right? So what in the world is the spinal cord? Well, the spinal cord is a long tube. Obviously, you could deduce that on your own.

Right? That's not why you're listening here. Right? But it's a long tube that basically grows from the, you know, medulla, you know, down the wheel to the lower, you know, the lower. But now just some key things to keep in mind, right? With a spinal cord, you want to make sure you know the blood supply. Remember, the spinal cord is actually supplied by the anterior and the posterior spinal arteries. You know, there are also many other arteries, but I would say maybe of all of them. The big one to know is the anterior spinal artery. Now, why is the anterior spinal artery important? Again, I'm going to try to, again, this is not going to be like a stock lecture. No, you know, I don't like to do those things. Those things are not the best ways to pass across knowledge, at least in medicine. Right? So I'm going to bring in the integrations as we go along. Right? So the anterior spinal artery, what's the big deal with it that you want to know for your exam? Well, you want to think about it in the context of a person that has had an abdominal eortic aneurysm fixed. Right? And then let's say they had like multiple bouts of hypotension during the surgery or the endovascular repair. Well, if you have that problem, that could potentially be problematic for a set patient. Why? Because the abdominal eortic, it gives off a pretty large artery. There's a big branch called the artery of a dhamcoids. Right? A dhamcoids is spelled as ADEM, KIE, WICZ, the artery of a dhamcoids.

The artery of a dhamcoids gives rise to the anterior spinal artery. Right? So if, for example, you're fixing a triple A and you mess up the artery of a dhamcoids, well, whoops, that's going to cause problems with the anterior spinal artery. And the person can lose everything except the dorsal column. Basically all the other pathways and tracts in the spinal cord just stop working. Right? The only thing that's going to be left behind is the dorsal columns and maybe some parts of the cortical spinal tract. Of all intents and purposes, everything but the dorsal columns will be remaining. Right? That's part of what we call the anterior spinal artery syndrome. Now, we know that the spinal cord has different parts. Right? The big parts, you know, there's the dorsal parts that are in the back. And then there's the ventral parts that are in the front. Right? Now remember, the dorsal parts are sensory. There's actually an embryologic reason behind this. But that's beyond the scope of my discussion in this podcast. So we're going to skip that. But basically the dorsal columns are sensory and then the more ventral parts are mortal. Right? The dorsal parts are sensory, the ventral parts are mortal. That's an important piece of information to know. Right? So we know that anything that has to do with sensation has to be dealing with the dorsal parts. Anything that has to be dealing with motor activity has to deal with the ventral parts. Right?

And then there's a few other minor details here and there that, you know, kind of importance to know. So let's start with the dorsal parts, right? Sensory. Well, I'm sure as you've gone through medical school, you've heard of this also fancy thing called the dorsal root ganglion. Right? The dorsal root ganglion. Now, it's a ganglion. Whenever you see the word ganglion or nucleus, it means that there's cell bodies there. Right? So the dorsal root ganglion is a ganglion on the dorsal of the back part of the spinal cord that has cell bodies of sensory fins. Right? So what are those sensory things? Well, those are things that pick up information from like the skin, from your arms, from your legs, all those things. Right? So they pick up information. Right? They pick up information. Right? So the pick up information and then that information comes up. Right? And you know, the cell bodies for those neurons that are picking up that information. Right? Those first cell bodies and the dorsal root ganglion. Right? And then many times as a role when you pick up information. Right? You will go and synapse. Right? This is like the thing is neurology. The input thing neurology is a bunch of memorization. It's really not. The neurology is really a bunch of principles with just wide application. Let me explain. Right? The thing is as a role just in general for most ascending pathways, be follow this role. Neuron 1 comes from the body. And then your own one goes and synapses on neuron 2.

And then when you synapse it's on neuron 2. Neuron 2 is going to dequeousate. This applies to pretty much every ascending tract that you're responsible for knowing for your exams. Right? Neuron 2 will dequeousate. And then your own 2 will go and hit up a body, somewhere in the thalamus, right? Like VPL or VPM or whatever. And then that fiber from the thalamus is going to go to somewhere in the brain. That's how it always works. Right? So you have information, goes through neuron 1. Neuron 1 synapses at neuron 2. Neuron 2 dequeousates. It ascends in the brain, goes to the thalamus, hits up VPL or VPM. And then those thalamic neurons go all the way to the cortex. Right? So let's maybe look at this specific kinds of information and how they travel. Shall we? Right? So the very first one, let's look at pain and temperature. Right? Pain and temperature. Right? That's the spinal thalamic tract. Right? It takes like crouped touch, pain and temperature information. Takes it from the body, right? The cell body is right? So the axons will pick up the information, take it to the cell bodies in the drossor organglyin. Right? And then you'll get into the drossal parts of the spinal cord. Right? Remember the drossal parts of the spinal cord are sensors. So it goes into the drossal parts of the spinal cord. And as it's entering the spinal cord, that's what we call the Lissauer Strat. It's spelled as L-I-W-S-A-U-E-R, Lissauer's, right? You know, an apostrophe and S-A-D and obviously, right?

Lissauer's tract, right? And those fibers, these synapse immediately. Right? So the pain, temperature, crouped touch fibers, the synapse on the second neuron in the spinal cord. Right? These synapse on that second neuron. Well, what did we say always happens to second neurons? Second neurons love to take you seats. Right? So the thing that's going to happen is that those, that second neuron is going to take you seat. It's going to cross in something we call the anterior-wide commissure. Right? Like literally in front of the central canal of the spinal cord. Remember, the central canal of the spinal cord is continuous with the sub-racinoid space for the most part. It carries CSF. Right? It carries a cerebral spinal fluid. Right? It carries cerebral spinal fluid. So the thing that happens is that, you know, it crosses the dacucetes in the anterior-wide commissure just in front of the central canal. And then it ascends all the way. Right? And the way it's ascending in the brainstem going on its way to the thalamus is actually going to be moving in the lateral brainstem. In a future podcast, you'll see precisely why this information is important. But it's going to ascending the lateral brainstem. Right? It's going to go to the thalamus. Right? To synapse on the third neuron. And then that third neuron from the thalamus is going to go to the cortex. Right?

And depending on where you're getting that sensory information from, that tells you where that neuron from the thalamus is going to go to. Right? So obviously, if you're getting information from like your face or your upper extremities, it's going to go to more lateral parts of your cortex. Right? A middle cerebral artery territory. But if you're doing more lower extremity sensation, it's going to go to more medial parts of your cortex. Right? That's the whole concept of the homonculus. Right? That's the whole concept of the homonculus. Right? Now again, it's very important to remember that spinothalamic tract travels in the lateral brainstem. This is extremely high yield to know for example, many people will be surprised. You wonder how did these people make it through neurology, not knowing this concept. Okay. Now let's talk about another ascending pathway. Well, another ascending pathway is what we call the drossal column medial limesca system. Right? This one, again, it works pretty much just like the spinothalamic tract, just a little different. Right? It's just different information in calories and the plastic decusity is also different. Now don't forget that anterior white commissar. I said it's literally in front of the central canal. Well, if you have a syringo maelia, right? You know, where you have like a cystic dilation of the spinal cord of the central canal of the spinal cord. That can begin to impinge on those fibers of the spinal thalamic tract. Right?

So the president will have a loss of pain, temperature and crutouch in a keep like distribution. Right? And remember syringo maelia is for whatever reason tend to be associated with carry one more formations. Right? But again, we'll probably deal with these lesions more in a different podcast, like a separate podcast on like spinal cord lesions. It's just all very high yield things for the exam. So now let's talk about the drossal columns. Well, the take information on vibration, on proprioception and on fine touch. Right? So vibration proprioception is spelled as pr o pr so pr o pr i o c e p ti o n proprioception. That sounds cool actually. Right? So vibration, proprioception and fine touch. It carries that information, right? Carries it, right? In the carries it carries it carries it. The axon carry that information, right? To the cell body, right? The first neuron, which is in the drossal organglyon. Right? And then the drossal organglyon, you know, those fibers moving to the spinal cord into the drossal parts of the spinal cord. Now remember, you can get fine touch, vibration and proprioceptive information from your lower extremities and from your upper extremities. Right? So the thing is those neurons, those axons of the original cell bodies, those, that neuron number one in the drossal organglyon. Those axons when they're in the spinal cord, they have different names, right?

If you're dealing with the lower extremities, fine touch, vibration, proprioception from the lower extremities. It's called the greysal fasciculus. Right? But if you're dealing with the upper extremities, it's called the kuni fasciculus. And it's actually kind of easy to remember where you're orientating the spinal cord, right? The great, your lower extremities are literally in the middle of you, right? Your upper extremities are more off to the side. So it makes sense that the greysal fasciculus is in the middle, is more medial in the spinal cord. And the kuni fasciculus is more lateral in the spinal cord, right? And those fibers, right? Again, there are still the axons of neuron one, right? Give no heat up neuron two. So you shouldn't be thinking about the causation just yet, right? But those fibers, the thing they do is they actually, they don't take your seat, they don't cross in the spinal cord like spinal thalamic does. Those fibers actually just go into the brainstem, right? And they go up immediately in the brainstem. That's very high heel to know. They go up immediately, immediately, immediately in the brainstem, right? Until they get to the medulla, right? They go to the medulla and then they synapse on the second neuron. Well, what's the second neuron called? Well, the second neuron, right? If you're dealing with the lower extremities, right?

Those axons from neuron one that are dealing with the lower extremities, they are going to synapse on the greysal nucleus in the medulla, right? And then the fibers for the upper extremities, right? Those axons from neuron one, you know, coming from those organglyons, those are parts of the spinal cord that are going to the medulla. They're going to synapse on the kuniute nucleus. And then the fibers from the greysal and the kuniute nucleus, right? That's neuron two, right? Neuron two, we said as a rule, neuron two, love to dequeusate. So those fibers are going to dequeusate. So many times they are called the internal acuate fibers. They're going to dequeusate in the cordomidola, in the lower parts of the medulla. And then they are going to ascend, keep going in the brainstem again. How do they traveling the brainstem? They travel immediately. And like any good-wise neuron two, what do they do? They're going to go to the thalamus. They're going to hit up their buddies at VPM and VPL. And then those thelomic fibers are going to follow the rules of the homunculus. And they're going to go to the cortex, right? I'm going to remember the anterior cerebral artery deals with the lower extremities and the penis. The middle cerebral artery deals more with the lower extrem- those more with the upper extremities, sorry, the upper extremities and the face, right? So those are the ascending tracts. Now what is the big descending tracts to keep in mind?

The big descending tracts to keep in mind is the corticospinal tract, right? It's a motor tract, right? And look at the name, right? Chodicospinal, right? So that means it's starting the cortex and goes to the spinal cord. That's why it's called literally the corticospinal tract, right? So if you think about it, this is literally a motor tract. So this is a motor tract. It's going to be going to somewhere that is a little more ventral in the spinal cord. Because remember, we established this rule at the beginning that the reversal parts of the spinal cord are sensory and the ventral parts of the spinal cord are modal, right? So what happens to that neuron one? Well, that neuron, you know, comes from the cortex, right? The thing is, this motor tract is more of a two neuron system, right? It's more of a two neuron system. Although that's not entirely true, but we're going to call it a two neuron system. That is true for the USMLE exams. We're not going to go into neurology residency slash fellowship level stuff here, right? But basically, neuron one, which is called the upper motor neuron, is going to start in the cortex, right? It's going to come down through the structure called the coronary diata, right? It's going to come down through the structure called the coronary diata, right? It's going to come in front of the cerebral pedoncles, right?

So if you're looking at the midbrain, those big bulges, those big like, almost like they look like breasts of the cerebral pedoncles, those are actually just corticospinal tract fibers, right? Now, what I want to say is that as those fibers are coming down, right? They also go through the posterior limb of the internal capsule. This is floridly high, you know, for your exams. They go through the posterior limb of the internal capsule. Well, why is that important to know? The posterior limb of the internal capsule has this fancy schmancy blood supply that is referred to as the lenticular striate artery, right? The lenticular striate artery. Well, why do we need to know about the lenticular striate artery? Well, the thing is that artery, especially people that are very hypertensive, remember the biggest risk factor for any kind of stroke is hypertension, right? The lenticular striate arteries, if you have really bad hypertension, they can bulge out and form an aneurysm. Many times you love to call these things charcoal, bushard, aneurysms, right? And when those aneurysms pop, you're going to cause a hemorrhagic infarction of the posterior limb of the internal capsule. Basically, those people, they're going to lose all mood sensation, right? On one side of the body. They're going to have what we call a dense paralysis, right? They're going to have what we call a dense paralysis.

They're going to have what we call a dense paralysis on the contralateral side of the body for reasons you will see in a bit, right? So you're going to come down through the cerebral peduncles, right? And those fibers, as they are traveling through the brainstem, they travel immediately in the brainstem. So this is the second medial thing I'm talking about in the brainstem. Don't forget your coricospinal tract travels immediately in the brainstem. Your dorsal columns travel immediately in the brainstem. But remember, your dorsal columns are sensory. Your coricospinal tract is model and then your spinal phylamic tract travels laterally in the brainstem, right? Travels laterally in the brainstem. So those fibers will come, come, come, come, come, come, come, come, come down. And then when they get to the medial ary pyramids, it's a more caught off part of the medial ary. They're going to cross. They're going to dequecee. Right? They're going to dequecee. They are going to dequecee. And then when did dequecee, they're going to come down, right, to the spinal cord. They're going to go to the ventral horn of the spinal cord. Because remember, they are motor fibers. So they don't really have much business in the dorsal parts of the spinal cord. They want to go a little more forward, more ventral parts. Right? So they're going to synapse on neuron two, right? Which is what we call the lower motor neuron.

That lower motor neuron is then going to proceed and go to the neuromuscular junction. And synapse on a skeletal muscle fiber. Right? It's going to release acetylcholine. Remember, I literally have a podcast on acetylcholine. Right? That's a very high-yield podcast to know. Right? Talk about like lambring it in my synagogues and all that fun stuff. Right? So again, very high-yield to know those things. Right? If you understand them, you're going to be in pretty good shape for your exam. And we're going to talk about lesions. We're going to talk about integrations about with this stuff in a future podcast. Right? I mean, there's many other spinal cord pathways, but to be honest with you, the in-gameies don't really care about those much. Right? There's like the tectospinal tract. There's the rubric spinal tract. There's the reticulos spinal tract. There's the vestibulospinal tract. But those are all very complex things, you know. I don't think those deserve a mention because they're more for like med school, basic science exams than a USMLE context. And then there's the spinal cerebellar tracts. And we talk about those in a future podcast. Right? But again, I really hope that this helps you establish a basis for understanding the spinal cord. I promise you the spinal cord is one of those things you want to understand going into your exam. I mean, I can even give you an example. If for example, you know the things that travel immediately and laterally, right?

Then you can begin to pick apart like these lesion questions they give in the brain stem in the spinal cord. It becomes like a joke to you when you just know these rules. Right? Like for example, right? If you see a person, yeah, tongue is not working. Right? And you see that, oh, they have like these upper motor neuron problems. That's going to localize lesion to the medial medulla. Easy. Why? Because you just take two pieces of information. You know that. Oh, they have a bone motor neuron problems. Oh, gee. That means the medial medulla must be involved because the corticospinal tract is a medial tract. And then you're like, huh, their tongue is not working. That's not good. Right? Well, that's going to be the hypoglossal nerve. Right? The hypoglossal nerve, right? It's crinion nerve 12. Right? As you'll see, it actually helps to know where crinion nerves are in the brain stem. Right? Remember, crinion 6 is in the medial ponds. Crinion 12 is in the medial medulla. Right? And multiples of six. Right? But then pretty much every other crinion nerve is in the lateral brain stem. Right? If we're looking at just ponds and medulla. Right? Like crinion 9, 10 and 11 in the lateral medulla. Crinion 5, 7 and 8 in the lateral ponds. Right? Remember, 3 and 4 for the most part are motor crinion nerves. So they in the medial midbrain. Right? Then the medial midbrain. Then the medial midbrain.

And one final thing I want to say is that pathway, that's superior cervical ganglion sympathetic tract, hunter syndrome causing pathway, actually travels in the lateral brain stem. That's very high autonone. It actually travels in the lateral brain stem. Again, you're going to see why basically today's goal was to lead down the rules. Now that you understand the rules, you'll see that in a future podcast, I'm going to help you make integrations with those rules. So as I do again, of every podcast, I do offer one or one tier in for many exams. Step one, step two, see case, step three, pre clinical, medical exams, 30-ish off exams. I offer again, you know, 24 hour review course, actually have one next week for step two, see case, step three and complex level two and three. And an NV Me test taking strategy scores next week Monday. And then for those that are taking the USMLE step two, see kill step three or complex level two or three exams in the summer. I have what I call a desk DISK school, the divine intervention step to see case school. It's going to be taking place in the first two weeks of May. It's going to be 75 hours long. But again, I really want to invest deeply in everyone that is attending the school. So I'm going to cut the number of people that can attend at 40. So if you're interested, just should be an email through the website and I'll give you some more information.

And then one other thing I would also say is I have this podcast on Apple podcasts on Google podcasts and on Spotify, at least the most recent 150. If you want everything from episode one, all the way to episode 371, then you want to go to the website, divineinterventionpodcast.com. If you have a Word Press account on your subscribe, you will get an email notification whenever I make a new podcast. And then another thing I want to say is that I have a You Tube channel. It's called divine intervention, USMLE podcast and videos. That's where I post the videos that I make. And then I have another website called divineinterventionlifelessens.com. Many people said, oh, divine, I really love the life lessons you put at the end of every podcast. And many of you have probably figured it out at this point. There's no big secret that I'm a Christian. So I decided to make a website where, you know, Bible, I use the Bible to explain just certain problems that are faced by humanity or certain character traits that will help you to be successful in life. Right now, I believe I have about 59 episodes, most of them are like 10 or 15 minutes long. And I even have the podcast on Apple podcasts is called the divine intervention, life lessons podcast. So thank you for listening to me today. A quick life lesson I have for you. Many of us know that today is Valentine's Day. Right? The key thing I will just say is show love. Right? Show love. If you're a Christian, love God. Right?

But show love to your fellow man. Right? Love your neighbor as you love yourself. That's just the truth. I feel like we live in a world where there's a lot of heat, these days. Where there's a lot of division where people are always fighting when one political party is fighting with the other, where one sect is fighting with the other, where one group is fighting with the other, where there's one war going here and one room of war going here. But I'll just encourage you show love to your fellow man. That is just the truth. Right? When you when when there's unity, success is inevitable. Right? But when there is this unity, right? Then failure is inevitable. Right? So just show love to your fellow man. Right? Just stop heating and start loving. That's the life lesson I will give you today. If you start loving one person at a time, I think the world that we live in is going to be a better place. So thank you for listening to me. Have a wonderful rest of your day. God bless you and happy Valentine's. Thank you.

Dorsal parts are sensory; ventral parts are motor.

It contains the cell bodies for sensory neurons that pick up information from the body (skin, limbs).

Neuron 1 comes from the body $\rightarrow$ synapses on Neuron 2 $\rightarrow$ Neuron 2 decussates $\rightarrow$ ascends to the thalamus $\rightarrow$ projects to the cortex.

The spinothalamic tract; it crosses in the anterior white commissure.

Lower extremities use the grácil fasciculus (medial); Upper extremities use the cuneiforme fasciculus (lateral).

The corticospinal tract.

The artery of Adamkiewicz (or Artery of the Adamcoids).

Vibration and proprioception.

In the Lissauer's tract, immediately upon entering the dorsal horn.

The gracile nucleus (part of the medial lemniscus system).

The corticospinal tract.

They are typically located in the medial structures (medial pons/medulla).

The artery of Adamkiewicz (or Artery of the Adamcoids).

Vibration and proprioception.

In the Lissauer's tract, immediately upon entering the dorsal horn.

The gracile nucleus (part of the medial lemniscus system).

The corticospinal tract.

They are typically located in the medial structures (medial pons/medulla).