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NBME 21 Answers

nbme21/Block 1/Question#50 (42.8 difficulty score)
A photograph is shown of a myelin-stained ...
Loss of sensation to vibration over both feet🔍
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 +4  upvote downvote
submitted by h0odtime(42),

Thoracic Cross Section Reference

  • Stem clue: Loss of vibration sense = Dorsal Columns
  • Image clue: pink (damaged) ventral horn area = gracile fasiculus (lumbar + sacral)
  • Gracile fasciculus in the dorsal column/medial lemniscus tracts carries information from the lower parts of the body (from T6 & below)
kacook1322  There is no stem clue as to loss of vibration sense +  



 +4  upvote downvote
submitted by haliburton(192),
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arezpr  thorax section +3  
guillo12  How do you know the gracile fasciculus is damage?!?! +2  
cr  which parte of the image its damage?, the pink? or black? +  
usmile1  the pink park yes +2  
d_holles  If you look at https://en.wikipedia.org/wiki/Gracile_fasciculus#/media/File:Spinal_cord_tracts_-_English.svg you can see that the closer to the center = legs, while further away = arms. +3  
hyperfukus  i still don't see where the damage is lol! FML +  
hyperfukus  i finally figured it out lol that was a slow moment i hope im not this slow on step yikes! +  
angelaq11  @hyperfukus I had the same problem at first, marked it and then came back. If you remember, in the spinal cord the white matter and gray matter are "reversed" compared to the brain. That said, if the butterfly shaped region (ie, the gray matter) is colored (in this case) lilac and the rest (ie, white matter) is blackish, the only thing that is actually abnormal, is the region where the dorsal columns are, because it stains just like the normal gray matter. After that, you have to think about which fasciculus is damaged, the gracilis or the cuneatus. The gracilis is medial while the cuneatus is lateral (picture someone with glued legs and open arms). Hope this helped +8  
azharhu786  Gracilus Fasciculus = Graceful legs +  
icedcoffeeislyfe  Check out FA2020 pg 508 Put simply--> myelin= black --> color of the normal white matter no myelin= pink --> color of the normal gray matter and the damaged area Dorsal columns= vibration, proprioception, pressure fine touch F. graciLis= Lower body F. cUtaneous= Upper body +1  



 +1  upvote downvote
submitted by ragacha(14),
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nor16  Cuneatus = Cervical, write into columns CG ( fron left to right) Cuneatus, Gracilis (CG) +1  



I had no clue where the damage was either, but with that said:

You feel the grass with your feet ––> gracilus

And the arrangement along the spinal cord is similar to the sensory/motor homunculus of the brain where the feet are on the inside/medial and the arms are on the outside/lateral.

drzed  Only in the dorsal columns; this is reversed if the decussation happens within the spinal cord (e.g. the spinothalamic tract has a somatotropic distribution where the proximal extremities are medial) +  



This is showing demylination/disruption (presumably from the spinal cord injury) of the fasciculus gracilis at the level of the lower thoracic cord. You can tell this is the thoracic cord because of the presence of the intermediate horn and the smaller ventral horns. It is the lower thoracic cord (below T5) because there is only one dorsal column.

We have only enough information to conclude lower leg involvement so loss of sensation to vibration over both feet is the best answer.






Check out FA2020 pg 508 Put simply--> myelin= black --> color of the normal white matter no myelin= pink --> color of the normal gray matter and the damaged area

Dorsal columns= vibration, proprioception, pressure fine touch F. graciLis= Lower body F. cUtaneous= Upper body