welcome redditors!to snoo-finity ... and beyond!

NBME 24 Answers

nbme24/Block 4/Question#49

A 27-year-old man sustains a spinal cord ...

Penile stimulation

Login to comment/vote.

 +18  upvote downvote
submitted by sattanki(46),

Apparently there is a completely separate spinal cord reflex where direct penile stimulation leads to an erection. This reflex only needs an intact arc in S2-S4, so as long as this region is not injured, an erection can still occur. However, with transection at C8, then the psychogenic erection reflex cannot occur, as this requires descending fibers from the cortex.

lsmarshall  Just saw a good summary of nerves/vessels involved saying, "pelvic parasympathetic fibers from S2-S4 can cause cavernous arteriole vasodilation via the cavernous nerve without of central stimulation." +4  
seagull  S2-3-4 keeps the penis off the floor +15  
drdoom  Modifying @seagull into iambic pentameter: “S2, S3, and Number 4 / keeps the big ole penis / off the floor” +  
myoclonictonicbionic  I can assure you the validity of answer (speaking from experience) +  
raddad  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4896089/ Under the "autonomic control" header +  

 +7  upvote downvote
submitted by cinnapie(13),

Why does every NBME have one or two erection related questions??

youssefa  Cause we all know what bout to happen to us in this exam :D +14  
niboonsh  lmfaooooooo +  

Apparently theres role of sympathetic system in psychogenic erection and its comes from T11-L2. So if patient have transaction at L5 they lose reflex erection but still retain psychogenic one.

ABove T9 transaction cause loss of psychogenic erection

charcot_bouchard  Below L5* (Not at) +