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NBME 23 Answers

nbme23/Block 1/Question#49

Electrical stimulation of the stellate ganglion is ...

Heart rate

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Notice that A) Bronchoconstriction, B) Glandular secretion, D) Peristalsis, E) Vasodilation of skin are all under parasympathetic control.

The only sympathetic control is heart rate, which would increase.

drzed  Vasodilation of the skin is under sympathetic control as well -- beta-2 receptors when stimulated cause vasodilation (via increase of cAMP in vascular smooth muscle). The key is recognizing that stimulation of a GANGLION of the pns will lead to release of NOREPINEPHRINE, which preferentially stimulates alpha-1 receptors. Those receptors will cause vasoconstriction. If the question asked what happens when you stimulate the adrenal medulla, the answer would be (potentially) vasodilation. This is because the adrenal medulla releases EPINEPHRINE which preferentially stimulates beta-1/2 receptors. +  
jesusisking  @drzed Awesome explanation except I think sympathetic response induces vasoconstriction in the skin though vasodilation in the muscles! +  

 +4  upvote downvote
submitted by seagull(716),

So, T1/2-T5/6 are the sympathetic level for the heart. The stellate ganglion are cervical sympathetic ganglion. This question seems more incorrect (or a huge leap) to me. But hey, I know people will disagree.

dentist  you're right! heart rate is the only option under sympathetic control. +  
drzed  The cervical ganglion is a fusion of the last few cervical levels and the first thoracic level, so it is plausible. +  

The way I excluded vasodilation was this: the sympathetic receptor that dilates is β2, which is not stimulated by norepinephrine. So to stimulate the receptor, the stellate ganglion would have had to first stimulate the adrenal medulla to release epinephrine (stellate too high to stimulate the medulla).

shriya goyal  nice explanation +1  
shriya goyal  nice explanation +  
shriya goyal  nice explanation +  
shriya goyal  nice explanation +  
krewfoo99  But isint beta 1 (heart rate) also stimulated by Epinephrine? +  

Stellate Ganglion is not involved in the regulation of heart rate: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2872892/ Gotta love those shit NBME questions.

drzed  Lol did you read the article: "the right stellate ganglion block (RSGB) decreased heart rate" +  

I incorrectly chose vasodilation. Found out that it’s actually vasoconstriction (vasodilation is parasympathetic):

Autonomic nerve fibers are also crucially involved in the regulation of vascular effects in the skin. Sympathetic nerve fibers release norepinephrine and/or NPY to innervate arterioles, arteriovenous anastomoses, and venous sinusoids which results in vasoconstriction, whereas parasympathetic nerves mediate vasodilatation through activation of venous sinusoides by the release of ACh and VIP/peptide histidine methionine.


I thought that the primary sympathetic innervation to the heart was through T1-T4. Why would stimulation of this ganglion not affect skin vessels in the upper limb?

methylased  Stellate ganglion --> sympathetics for sweat to skin in UE + head. Apparently also to increase HR (some cardiologists ablate stellate ganglion for tachy that cant be controlled by beta blockers). +  
tea-cats-biscuits  The stellate ganglion is a sympathetic ganglion, so it wouldn’t increase vasodilation in the skin of the upper extremity. Also in most people, the inferior cervical ganglion is fused with the first thoracic ganglion (T1), forming the stellate ganglion. +7  
sympathetikey  Got this wrong too. I think upper extremity skin vasodilation (which I picked) is probably more due to local metabolites. +  

 +0  upvote downvote
submitted by criovoly(10),

the stellate ganglion is part of the sympathetic nervous system flight or fight. Increase heart rate is the most obvious.