DIP Episode 44 - USMLE Anatomy Series Part 1

Okay, welcome. My name is Devine. I am a PGY1 resident and this is the 44th episode of the Divine Intervention Podcasts. In today's episode, we're going to be starting something I call a USM Lian Anatomyous series. I will see this series of podcasts, especially applicable to people taking step one or or surgery shelf or OBGYN shelf or step two. The thing is really like Anatomy is hard to prepare for. It's just one of those things that crop up at like weird places. You may even see like some Anatomy-related questions like one or two on a medicine shelf. So I just sort of took it upon myself to sort of try to like make a series of podcasts that highlight these high-yout classic Anatomy scenarios that pop up on these NBM related exams and then discuss them. But the thing is Anatomy is Info Dense. So I'm going to do this in bits and pieces, right? So to just make the material more digestible. So it's not like I'm flooding you with a ton of information at one. So today we're just going to consider some high-yout scenarios and go from there. So the first question says assuming a patient has restriped what is the lesion brichial plexus nerve? Well I hope you're thinking about the the radion nerve, right? And the high-yout extensor in the upper extremity that actually stops functioning with a lesion to the radion nerve is actually the triceps, right? So remember your radion nerve, I sort of think of it as the best nerve, right?

So the B for brichial radialis, the E for your extensors, the S for your supinator, okay? And T for your triceps. Those are the things that are controlled by the radion nerve. Now what is the classic humoral fracture pattern associated with this nerve lesion, right? So remember if you have a mid-shabbed fracture, very high-youturner, that a mid-shabbed fracture of the humerus can cause a radion nerve lesion. And then in terms of sensory losses in a patient that has a radion nerve problem, right? They will lose sensation on the dorsum of the hand, relating to the first three and a half digits, okay? So not on the palm of surface of the hand, the dorsal surface, right? So like the back of your hand, of the first three and a half digits, you lose sensation in those regions if you have a radion nerve problem. And as true, so this one is just as trivial, I don't think I've ever seen this show up, but just one of these things that you sort of have like this sensation within your stomach that you may pop up on a weird example, like a pit shell, for example. So it's trivia, for a pit shell, for a step two CK. Audio diagnosis being a child with generalised paper, slash PTKI. So those are, that's essentially telling you that the patient has like thrombus sideopenia, right? And they tell you that there's no radios, but pivoting the left upper extremity, okay? That's something known as a tar syndrome. It's called like thrombus sideopenia absent radio syndrome.

Some, you may see some resources referred to it as like tetra focomilia absent radios, right? So just remember like low platelets, no radios is thrombus sideopenia absent radios is a rare disease, it's a rare phenomenon, but it's just one of those things I sort of have this feeling that the NV Me me want to test on some example. And then Saturday night palsy, it's a classic presentation of a radion nerve injury. It's just a person that let's say they take too much alcohol and then they pass out and then they put an axilla on top of like a bench, right? And then they have like compression of the radion nerve at that region and then they get into trouble. So those are all the questions for this slide. Next one. Now what is the damaged nerve in a patient with a surgical neck fracture of the humerus, right? So this is the axillary nerve. I just just remember like the word snap, right? Surgical neck that's SNN and then the A stands for axillary, okay? So if you snap, right? So surgical neck fracture, you damage the axillary nerve. The two high-yield muscles supply by this nerve, you should definitely know these, right? So your deltoids and your teris minor, okay? And the axillary nerve actually runs along with the posterior circumflexumural artery, that's a high-yield tidbit you want to know. It's just again one of those bizarre things they love to test in an anatomy.

And then the quadrangleous space, okay, is actually a space that loves the transmits like the axillary nerve and transmits like the posterior circumflexumural artery and vein. And then if you have like an anterior shoulder dislocation, right? That's a classic cause on exams of an axillary nerve injury. Remember the most common kind of shoulder dislocation is an anterior dislocation, okay? The only time you get posterior shoulder dislocations on exams is if they give you that a patient was like having a seizure or they were like victims of a lightning strike for example, okay? Or they were electrocuted. Electricity is the thing that classically causes a posterior shoulder dislocation. But don't forget that the most common kind of hip dislocation is a posterior dislocation. And tear-hip dislocations are much less common than posterior hip dislocations. Now, the sensory association on the axillary nerve, right? So if you describe a patient that has anesthesia on the lateral arm, okay? Think about an axillary nerve injury. If you describe a patient with anesthesia on the lateral thigh, right? Hopefully that makes you think about a lateral femoral cutaneous nerve injury. Now, the associated words for the axillary nerve with the bricchioplexus, right? That's C5 and C6. Okay, good. Next one. Now, exits for the 12 preneoners from the skull, right? So this is easy step one further. You can just begin to imagine that this is something they may want to test on an exam.

So the exits of the preneoners from the brainstems, super high you to know those. So let's just run through those relatively quickly, right? So the first preneonerve is the olfactory nerve, right? And remember that exits the skull through the crib from plate, okay? The second preneonerve is the optic nerve, okay? That's the one that leaves the skull through the optic foramen. Some people call it optic canal, doesn't really matter. And then the third cranio nerve goes through the superior abdominal fissure. In fact, I'm just going to group a couple, right? So the superior abdominal fissure transmits the oculumur nerve, which is cranio nerve 3, the trochlear nerve, which is cranio nerve 4, the first branch of the trigeminal nerve, right? So that's the ophthalmic nerve. That's like cranio nerve 5, like V1, okay? And then it also transmits the sixth cranio nerve. That is the abducent nerve, okay? So superior abdominal fissure transmits cranio 3, oculumur nerve, cranio 4, trochlear nerve, cranio 5, first part of the ophthalmic nerve, and cranio 6, the abducent nerve. Please do not confuse the things that go through the superior abdominal fissure with the things that go through the cavernous sinus. The cavernous sinus transmits the oculumur nerve, cranio 3, trochlear nerve, cranio 4, ophthalmic nerve, that's the first branch of the trigeminal, and the maxillary nerve, which is the second branch of the trigeminal.

The cavernous sinus also transmits the internal corroded artery in the middle, and the abducent nerve in the middle as well, okay? So basically all the cranio nerves that are transmitted through the superior abdominal fissure, are transmitted through the cavernous sinus, but the superior abdominal fissure does not transmits the maxillary nerve, which is the second branch of the trigeminal nerve, very high you to know that, so don't mix those things up. And then going on to the other cranio nerves, right? So like the maxillary nerve is transmitted through forimin rotandum, that's the second branch of the trigeminal. Forimin ovale transmits the mandibular nerve, right? That's the third branch of the trigeminal nerve, and then the facial nerve exits the skull through the stylo mastoid forimin. Remember the facial nerve passes through the parodid gland on its way out of the brain, but it does not interview the parodid gland. It's very high you to know that the parodid gland, I believe, is interviewed by the glossopharyngeal nerve, that's cranio nerve nine. And then the facial nerve, right, leaves the, so I've talked about the fissure nerve, the vestibulococluon nerve, right? So that's cranio nerve eight, leaves the skull through the internal auditory canal, okay? Actually believe it or not, some people actually say that oh, the fissure nerve also cuts through the internal auditory canal.

So if we're you for cranio nerve seven, the fissure nerve, I will remember internal auditory canal and stylo mastoid forimin. And then for the, for cranio nerves nine and ten, right? So cranio nine is the glossopharyngeal nerve, cranio ten is the vagus nerve, those nerves are transmitted through the juggler forimin, okay? The juggler forimin also transmits cranio nerve eleven, which is the spinal accessory nerve, okay? It's kind of like an explicit spine-on nerve if you may. And then the hypoglossocanal transmits the twelfth cranio nerve, which is the hypoglosso nerve. So very, very high you to know these cranio nerve exits. And then I've talked about cranio seven caused through the parodid gland, talked about the carbon as sinus business, talked about what runs through the middle of the carbon as sinus, right? So basically your internal curly artery, okay? And you have duces nerve, remember you have duces nerve innervizio lateral rectus muscle. So that controls A Bduction of the eye. Now as an aside, right? So this is a very high-old algorithm that I think will probably help people that are preparing for step one, but most likely more, I guess more likely step two, because most people that are taking step two, step three, they forgot to know the neuroanatomy, they learned in med school. So this algorithm sort of cuts out a lot of the thinking you need to do and kind of makes your life easy, right?

So the thing is if you get a question and they're trying to get you to localize a lesion in the brain stem, like, oh, like what's the artery or what's the region of the brain stem blah, blah, blah? They're just certain things you can do. If you sort of answer these questions and follow the stepwise algorithm, you'll almost always be able to get these questions correct, right? So the first question I asked myself is do these patients have Power Point problems? And by Power Points, I mean like p p t, like the mnemonic, right? So the p stands for pinprick, the other p stands for pain, the t stands for temperature. If they have any of those problems, okay, that tells you that the problem is in the lateral brain stem. If they don't have any of those problems in the question, that means the issue they have is in the medial brain stem. So if a patient again has pain, pain prick and temperature problems, the issue is in the lateral brain stem. That's the first decision you're trying to make. Is it the problem in the lateral brain stem or in the medial brain stem? And then the second question you ask yourself is is there a craniotid, I can pick out from this question stem in front of me? Most people are pretty good at saying like, oh, yeah, if they have like a problem, the gag reflex, it's probably like craniotid of 9 or 10. So the issue has to be in the in the medial right?

Or oh, if they have problems with like facial sensation blah blah blah, you know the problem has to be in the p p p t, right? And then don't forget that your midbraight is what contains craniotid of 3 and 4. So basically by answering questions 1 and 2, you can tell yourself, oh, is it? You can basically come up with the fact that oh, you may have a problem in the lateral medulla or in the lateral ponds or in the medial medulla or in the medial ponds, okay? Just by answering those first two questions. And then the third question you ask yourself is you use a key, okay? The key is that if you combine your answers to step 1 and 2 and you end up with lateral medulla as your answer, okay? The artery that supplies that region is paica, right? So the posterior inferior cerebellar artery or you can just basically go with a more proximal thing, right? The vertebral artery, the vertebral artery gives rise to paica. If the answer you come up with is medial medulla, you're thinking about the anterior spinal artery. Remember those come off the vertebrates. And then if the answer you come up with is lateral ponds, you're thinking about eica, the anterior inferior cerebellar artery, okay? And then if the answer you come up with is medial ponds, right? So lateral ponds is eica, anterior inferior cerebellar medial ponds is, let's see, those will be the permedian punty notters, okay? Or they may say basilar artery, okay? So just sort of keep those things in mind.

Really, if you answer those three questions, for the most part you can narrow down answers pretty easily on these exams. One other thing you can just throw in there is pin and temperature sensation for the face is usually epsilon-ateral. Pin and temperature for the body is usually contralateral, right? So if for example, they're like super specific in the question and you're like, oh, you need to figure out if the problem is on the left side of the brainstem or the right side of the brainstem, then you probably need to remember that extra piece of information, right? Because remember, your spinal thalamic tract which controls pin and temperature information for the body, right? It sort of enters the spinal cord as liss-our-stract and then it crosses in the anterior white commission before it ascends, right? So because it is crossed, pin and temperature information for the body is contralateral. So if the loose sensation on like the right side of the body with respect to pin and temperature, then you know the lesion has to be on the left side in the brainstem. So just combine those things, I think that will help you a lot, especially those prepared for step two or like a neuroshelf. Now the epiplytic foramen, again, this is more classically something that could show up on a surgery shelf or in step one, okay? The epiplytic foramen, the high-yield thing you want to know about is that it's like posterior to the hepato-duadno ligament, right?

So I mean, you don't, again, you don't need to memorize this blingy. Hepato-duadno ligament, that tells you that it's a ligament that connects the liver to the duodenum, simple as that, right? So the epiplytic foramen is behind the hepato-duadno ligament and the thing is it essentially serves as a conduit between the greater and the less momentum, okay? So those are, that's just a big function. But the annoying thing on the example is they love you to know the boundaries of the epiplytic foramen and there are four boundaries you need to know, right? So I already talked about what I already said that this foramen is posterior to the hepato-duadno ligament. So that already tells you that the hepato-duadno ligament has to constitute the anterior border of the epiplytic foramen, okay? The superior border is actually one of the lobes of the liver. It's like the codic lobe, right? So if you remember back to anatomy from first year, you probably remember learning about the codic lobe of the liver and the codic lobe of the liver, the codic lobe of the liver is what constitutes the superior section of the epiplytic foramen. And then the hepato-duadno ligament, right? I said he considers the anterior portion, do not forget that ligament is what contains the portal triad, right? So like your hepatic artery, your portal vein, and your bowel duct, okay? So you sort of keep that in mind.

And then the inferior, the posterior border of the epiplytic foramen is the peritoneum that covers the inferior veniciva, okay? So you may feel like pulses from the inferior veniciva if you sort of go to the posterior border of the epiplytic foramen. And then the final one is the the inferior border, the inferior border of the epiplytic foramen. And again, I'll run through these again. The inferior border is like the first part of the doodina, okay? So let's run through this real quick, right? So the anterior border of the epiplytic foramen is the hepato-duadno ligament, which contains the portal triad, right? Which is the hepatic artery, portal vein, and bowel duct. The posterior boundary is the peritoneum that covers the inferior veniciva, okay? The inferior boundary is the first part of the doodinum, okay? And then the superior boundary is the codiclobe of the liver. Again, I promise you it is very high to know these things. Now next question, what is the cranial nerve that carries the general sensation of taste? So general, not special, general sensation of taste from the anterior to the third of the tank, okay? This is the trigeminal nerve, right? And to be more specific, this is the mandibular nerve. The third part of the trigeminal nerve, the associated ganglion is the trigeminal ganglion, easiest pie. Now, the nerve that carries the special sensation of taste from the anterior to third of the tongue, that is the fischo nerve.

If you want to get a little more specific, that's the cordectimpani branch of the fischo nerve. Now, what is the cranial nerve that handles both the general and special sensation of taste for the posterior third of the tongue? That'll be the ninth cranial nerve, right? So that's your glossopharyngeal nerve. Although the vigus nerve, like in the very back of the tongue, it also handles some sensation of taste. And then the cranial nerve that handles most of the motor inhibition of the tongue, right? That's the hypoglossal nerve, right? Remember the hypoglossal nerve is medial in the brainstem. Most of the motor cranial nerves are located medially in the brainstem. That's kind of a high-alt facts to know, right? So, like if you look at the medulla, the hypoglossal nerve is in the medial medulla, it controls the motor function of the tongue, right? The abducense nerve is a motor nerve. It's in the medial ponds, okay? So that's just again, there are certain principles that on the liveaus, but I don't really have the time to discuss those in this podcast. Now, the one exception to the Rulis Palato glossos, right? So if you sort of step back to anatomy, you'll probably remember learning about some stern, so they're kind of easy, my memory. But you probably remember learning about some stern loss that relates to cranial nerves, where like, oh, if a cranial nerve has like tenser in the name, I believe it's innervited by like some branch of the trigeminal nerve.

And then, so like, tenser timpani, tenser viali palatine and all that stuff. And then if a cranial nerve has like palat in the name, it's most likely innervited by the, by the vagus nerve is only if Rulis applies and Rulis is like the tenser law. So like, tenser viali palatine is innervited by cranial five, not cranial 10, because that Rulis applies first over Rulis too. I sort of think of that like in the context of those solubility principles, you probably had to learn in college during a general chemistry course. Okay, now, so the exception to that Rulis, the, again, the hypoglossal nerve does all the muscles of the tongue, all the intrinsic muscles of the tongue, with the exception of the palatoglossus, that's done by vagus nerve, that's cranial 10. And then if a patient has hypoglossal nerve lesion, the tongue would give it towards the side of the lesion, okay? The classic nummonic for that is like leaking your wounds, okay? So again, super high you to know this stuff. Now, a patient with a history of morphine or tertiary syphilis or Earlis d'Anglus syndrome or a long history of smoking presents with six months of hoarseness, right? So hopefully you're thinking about some kind of, some kind of aortic arch problem, right? Remember, the biggest risk factor for an abdominal aortic aneurysm is smoking, right? So smoking increases the person's risk of having aneurysms of the other.

So I even tell you here, PA lateral chest x-ray is consistent with an ascending aortic aneurysm that includes the arch, right? So the question here is what is the underlying mechanism behind a patient's hoarseness? If you're taking step one and you do not know this and not to me, not any detail, let's just say you may not have a very good experience because this is something that's tested pretty commonly, right? So obviously if I'm referring to hoarseness, I'm referring to the recurrent laryngeonurves, right? And we know that the recurrent laryngeonurves are branches of the vigorous nerve, but they sort of act in different ways, right? So the left recurrent laryngeonurve, it actually loops around the aortic arch, but on the right, the right recurrent laryngeonurve actually loops around the right subclavian artery, okay? And then it loops upwards. Now, the thing is the recurrent laryngeonurves, they supply sensation to the larynx, below the vocal cords, although, excuse me, although they also supply the posterior cryocryptoid, the posterior cryocryptoid, are the muscles that open the vocal cords, okay? So if a patient has an aortic arch aneurysm, you may potentially compress the left, not right, the left recurrent laryngeonurve, okay? And you can cause hoarseness because you essentially cause in, by screen of the left recurrent laryngeonurve, you're screen of the posterior cryocryptoid, so you cannot open the vocal cords appropriately, okay?

So it's super, super, super high, you to know that. And the cranial nerve that supplies most sensory information to the larynx is the vigorous nerve, okay? Simple as that. Now, next question, a 35-year-old female G2 P1 at 40-weeks gestation is in labor. She has a long history of polycontrol type 2 diabetes. The fetus is currently a tube plus 2 station with a decision made to proceed with four-seps delivery. That's pretty painful. To obtain adequate pain control around the perineum, vulva, and vagina, with the use of local anesthesia, what is the most appropriate nerve block procedure, right? So again, this is a classic step one question, right? So this patient has, is about to undergo a pretty painful procedure around the perineum, vulva, vagina. So for those procedures, right? You probably want to do something on a pew dendonurve block, okay? It's kind of like you can essentially use like a lightokin, for example. You can use local anesthesia. And the thing is, usually that block is done around the isho spine, okay? That's a high-yield detail you want to remember. It's done around the isho spine. The isho spine, remember, it's a thin that, around like the exit of the bunny pelvis, is the thin that sort of like devise the greater and the lesser sciatic for ramynah, okay? So again, high-yield to know that pudendonurve block around the isho spine. Super high-yield detail to know for, especially for step one.

Now, I'll imagine it's a high-yield detail to know for step one on verse or just shaft. Now, next question, coronary arteries, right? So you should know that they are perfused during dastily, okay? They are essentially squished during systole. So you don't perfuse myocardium during, during systole, okay? But during dastole, that's when you perfuse myocardium, okay? And during dastole, right? If you're sort of looking at things at the voivular level, at that point, the mitral, so let's assume we're looking at the left side of the heart, right? The mitral valve will be open, right? During dastole, but the yodic valve should be closed, right? Because you don't want backflow of blood during dastole, okay? So the yodic valve is closed, but the mitral valve is open. Now, next question, a surgery resident is tasked with performing a mastectomy with axillary lymph node dissection, and a 40-year-old female with biopsy proven invasive doctor carcinoma. This is the most common kind of breast cancer in the US. Now, what are the two high-yield nerves that may be injured during this procedure? And how will these present clinically, right? So, again, classic step one question, classic surgery shelf question, or classic pain-forder, if you're going for a breast surgery case, right? So there are multiple nerves you can injure during these procedures with the two most common ones, or I guess, classically tested ones are one, the long thoracic nerve.

Remember that controls the serirator's anterior muscle. So if you have issues with that, you have like winged scapula, okay? And then the second high-yield nerve is the thoracodorsal nerve. That supplies the latissimus dorsi muscle, okay? And if you have injury to that nerve, you have problems with like extending or internally rotating or AD, not AB, AD, like, right? So, like anode dominion, right? So like AD ducting the the shoulder joint. So you have issues with extending internally rotating and adducting the shoulder joint, okay? So thoracodorsal nerve, latissimus dorsi, long thoracic nerve, serirator's anterior winged scapula, right? And that serirator's anterior long thoracic relationship, you can remember with the common mnemonic salt. So serirator's anterior long thoracic, okay? It's something you're probably learning your first year of med school. Now the last question here today, a 23-year-old male is mistakenly struck in the head during a baseball game with a bat. He initially loses consciousness for two minutes when he was able to finish the game. We've all heard this story before. Two hours later, he's rushed to the ED after the sudden onset of repeated fits of vomited. Let's assume this patient is unconscious, right? So, what's your diagnosis, right? So obviously this is an epidural hematoma, okay? And remember, this arises from a transaction of the like middle meningel artery.

Remember, this is actually a branch of the the maxillary artery and the maxillary artery is actually the terminal branch of the external crowded artery, okay? So the external chloride, the curated artery, its terminal branch, I believe, is the maxillary artery and the middle meningel artery is a branch of the maxillary artery, so if you translate the middle meningel artery, you have an epidural hematoma. This is the classic we present on exams and it shows up as a lens shaped hematoma on imaging, okay? For sub-dural hematomas, right? So this is like lower pressure bleed, it's like the bridge in veins, that's the classic exam buzzword and it looks crescent shaped on imaging, like on a CT scan, and the classic exam scenarios, right? So shaking baby syndrome classically presents as a sub-dural hematoma. If a patient is an alcoholic, right? Alcohol causes like shrinkage of the brain, right? If a patient is also like old, right? People on the go bring a trophy as they get older, right? So those things, right? If you have a small brain in a fixed box, which is like the skull, as the brain sort of like dangles in that box, you can share those bridge in veins and you can cause a chronic sub-dural hematoma, okay? So those are the higher scenarios you want to keep in mind.

So again, bite-sized piece of anatomy, I'll try to make other podcasts on this material as time permits and hopefully ultimately have like a relatively thorough, like taking all these podcasts together, like ultimately have something that's relatively thorough in terms of anatomy for these MBME Bs and exams. So I wish all the best for the rest of the day and for those taking step one or step two or step through expecting the scores tomorrow, which is a Wednesday because I'm obviously recording this on the Tuesday and we show the best, have a wonderful day and God bless. Keep shining. Thank you.

Mid-shaft fracture of the humerus.

Axillary nerve.

Hepatic artery, Portal vein, and Bile duct.

Lateral femoral cutaneous nerve.

Aortic arch aneurysm.

Glossopharyngeal nerve (CN IX).

Oculomotor nerve (CN III), Trochlear nerve (CN IV), Ophthalmic nerve (V1), and Abducens nerve (CN VI).

The superior orbital fissure transmits CN III, IV, V1, and VI. The cavernous sinus also transmits the Maxillary nerve (V2) and the internal carotid artery/abducens nerve.

Triceps, wrist extensors, supinator (TRES).

Hepatoduodenal ligament.

Thoracodorsal nerve (supplies latissimus dorsi).

Epidural (Middle meningeal artery) and Subdural (Bridging veins).

Oculomotor nerve (CN III), Trochlear nerve (CN IV), Ophthalmic nerve (V1), and Abducens nerve (CN VI).

The superior orbital fissure transmits CN III, IV, V1, and VI. The cavernous sinus also transmits the Maxillary nerve (V2) and the internal carotid artery/abducens nerve.

Triceps, wrist extensors, supinator (TRES).

Hepatoduodenal ligament.

Thoracodorsal nerve (supplies latissimus dorsi).

Epidural (Middle meningeal artery) and Subdural (Bridging veins).