sympathetic nervous system and urination?

[faisal 2000]

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why in fear situation, person will need to go bathroom. is there relation between sympathetic nervous system and urination?
by the way sympathetic nervous system will close the valves and in the body so how can they lead to urination in these case ??

 

[Gdl88]

Sympathetic system increases renin released by the kidney by beta receptors, doing this RAS system increases the perfusion of the kidneys and gfr rate.

 

[mcloaf]

Sympathetic system increases renin released by the kidney by beta receptors, doing this RAS system increases the perfusion of the kidneys and gfr rate.

While true, I doubt the time scale of hormonal regulation of GFR is such that if you're about to get eaten by a mountain lion you suddenly increase GFR so much as to overload the bladder and leak through a contracted internal urethral sphincter (not to mention that my understanding of this phenomenon is that it's not just a bit of leakage but full-steam-ahead bladder voiding, which you wouldn't expect if you were merely increasing GFR in the face of a contracted urethral sphincter).

Anyway OP, the best I found on google was http://www.slate.com/articles/news_..._they_re_scared_.html?tid=sm_tw_button_chunky
It's not clear to me that mechanism is understood in much more depth than "your brain does crazy **** when it's reacting to a really strong fear stimulus."

Hopefully someone else here knows more than I do.

 

[Apoplexy__]

Not sure, but I wouldn't bother trying to understand it. It could just be one of those things like vasovagal syncope. Why does the body respond with an overwhelming surge of PARAsympathetic activation in response to fear/surprise in syncope, but sympathetic activation in every other?

Because f*ck you, that's why.

 

[BlueJay25]

@mcloaf is right. The sympathetic stimulus through B1 receptors increases renin release from the juxtaglomerular apparatus. This would activate the RAAS system leading to Ang II and Aldosterone which would increase GFR. But we have to remember that through alpha1 receptors all the sphincters (including the urinary sphincter) would be tightly shut. This would actually inhibit urination and defecation which is the case with most people. They do not urinate/defacate in a frightened situatuion. Very few people actually experience urination during fight/flight situation.

The answer to this "frightened urination" comes from neuro. Now I'm not sure if this is ENTIRELY accurate, but this is my understanding. The Pontine micturition center (PMC or Barrington's Nucleus) is located in the brainstem and has some control over urination. Now when you bladder distends a lot, the receptors fire and the PMC cause urination via contracture of the bladder and relaxation of the sphincter. Another innervation here is also the frontal cortex which would not allow the PMC to let you urinate in a situation where it is not socially acceptable by keeping the voluntary urinary sphincter contracted via inhibition of the PMC pathway. Now along with this, we also have the limbic system which has been hypothesized to be in charge of our "fight/flight system". Now here is where I'm not 100% sure if this is what happens but, this is best explanation I've gotten: The limbic system starts firing like crazy which actually messes with and inhibits the signals from the frontal cortex (which normally inhibits the PMC pathway in a non socially acceptable situation). So now your PMC is in charge and if there is bladder distention, the person will urinate.

I hope this helped.