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NBME 24 Answers

nbme24/Block 2/Question#18 (42.7 difficulty score)
A 68-year-old man has loss of pain and ...
Right dorsolateral medulla🔍,📺
tags: FA20p504 

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submitted by m-ice(346),
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The etaitnp sha lsso fo pina dna muraetpreet no teh tgirh dies of ihs eac.f Ssitnenoa of eht afec is ateslir,lpai os het eiuss smut eb no eth pttseia'n htrgi ,sdei hcwih ew can ncimfor by nwnikog hatt anoiessnt fo eht doyb si tc,aotrlnalaer and eh ash otsl fetl isdde inap adn emtrrueapet fo the .dbyo

Pian dna tremtrepeau entonsias of hte ydob is rtpa of the athlsicanpmio ctt,ar hchiw lwasay urns rtllaealy uhorthg eht b.tiresanm hTis anc eb fcdenroim yb ergenmeirmb htat oeinstasn to eht cfea olas surn lrleatayl ghtuhor the a.tinbmesr oS, we nca mincrof tsih si a gthir dieds etalral nbtimrsea esusi.

ehT ssol fo gga xeefrl adn lisraaysp fo teh olavc socdr milyp mreiniatpm of anicrla enervs XI dan ,X thob of hihcw liacolze to the udaell.m fe,ereThro teh snewar si ghrit ldaolortersa mle.audl

duat98  You're a good man. +5  
charcot_bouchard  You must be handsome too +12  
amy  The dorsal vs ventral is confusing! +  

submitted by cassdawg(1381),

"Simple rules of the brainstem" (credit to our anatomy gods at UofL for organizing, also this image is fucking great for visual learners):

  1. There are 4 structures always in the ‘midline‘ beginning with M
    • Motor pathway (or corticospinal tract): damage results in contralateral weakness of the arm and leg
    • Medial Lemniscus: damage results in contralateral loss of vibration and proprioception in the arm and leg
    • Medial longitudinal fasciculus: damage results in ipsilateral inter-nuclear ophthalmoplegia (failure of adduction of the ipsilateral eye towards the nose and nystagmus in the opposite eye as it looks laterally)
    • Motor nucleus and nerve: damage results in ipsilateral loss of the cranial nerve that is affected (III, IV, VI or XII)

  2. There are 4 structures to the ‘side‘ (lateral) beginning with S
    • Spinocerebellar pathway: damage results in ipsilateral ataxia of the arm and leg
    • Spinothalamic pathway: damage results in contralateral alteration of pain and temperature affecting the arm, leg and rarely the trunk
    • Sensory nucleus of CN V: damage results in ipsilateral alteration of pain and temperature on the face in the distribution of CN V (this nucleus is a long vertical structure that extends in the lateral aspect of the pons down into the medulla)
    • Sympathetic pathway: damage results in ipsilateral Horner’s syndrome, that is partial ptosis and a small pupil (miosis)

  3. The rule of CN 4’s (also found in FA2020 p504)
    • 4 cranial nerves in the medulla (IX-XII)
    • 4 in the pons (V-VIII)
    • 4 above the pons (2 in the midbrain= III, IV, 2 in the cortex= I, II)
    • The 4 motor nuclei that are in the midline are those that divide equally into 12 (except I and II), including III, IV, VI and XII (V, VII, IX and XII are in the lateral brainstem)
cassdawg  Sorry for the formatting fuck up +1  
drdoom  @cassdawg best to avoid doing nested lists. website doesn't seem to like that :P better to start a “brand new” list for each little subsection kinda thing :) p.s. congrats on your MVP of the Year Award! +2  

Wow can we talk about how amazing this image is? Thanks for sharing!

+/- motherhen(49),

submitted by brethren_md(94),
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teLalra arelMdluy odyrSmen geWe(brll)na - ees FA fro roem s.idelta ptmymsSo ofr tsih sreymdno amhtc up wtih hwta is gnibe petsee.nrd

submitted by charcot_bouchard(478),
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I etg hwy sit tlearal tbu ondt all racnial neevr eepctx 4 rsaei lt?eVrnlay FTW etyh dda siht osrDo obefre elratl?a

qfever  I think it's the nucleus affected in lateral medullary syndrome (instead of the nerve axons) +  
nerdstewiegriffin  Because in the medulla section the nucleus is dorsal motor nucleus of X +  
doctordave  They all exit the brainstem ventrally, but the nuclei can be located deep within the brainstem +  

submitted by welpdedelp(242),
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Thsi swa laetlar mdauellr ryodesmn aka oardlotelasr tcfairn fo eth A.ICP

submitted by abhishek021196(79),

Posterior inferior cerebellar artery [PICA] supplies

  1. Lateral medulla
  2. Nucleus ambiguus (CN IX, X, XI)
  3. Vestibular nuclei
  4. Lateral spinothalamic tract, spinal trigeminal nucleus
  5. Sympathetic fibers
  6. Inferior cerebellar peduncle

Damage to PICA causes Lateral medullary (Wallenberg) syndrome.

Dysphagia, hoarseness, decreased gag reflex, hiccups. Vomiting, vertigo, nystagmus decreased pain and temperature sensation from contralateral body, ipsilateral face. Ipsilateral Horner syndrome. Ipsilateral ataxia, dysmetria.

Nucleus ambiguus effects are specific to PICA lesions.

“Don’t pick a (PICA) horse (hoarseness) that can’t eat (dysphagia).” Also supplies inferior cerebellar peduncle (part of cerebellum).