emptymalei/为什么男人小便的时候，会打激灵呢？

## 为什么男人小便的时候，会打激灵呢？
尿颤用 @赵研™ 的那个解释我一直很怀疑。

1. 如果尿的温度比其它部分高，那么尿确实是热源。但是即便水的热容很大，可以作为很好的热源，那么我们认为人的膀胱充满尿液的时候体积为 400ml [^1]，那么对应的表面积为 180cm^2 （仅仅对球形的膀胱适用……）。再假定人的膀胱厚度 2mm（充满尿液），与膀胱外组织温差 1℃，导热系数 3000 J/(m s ℃)？？？？？？。这样算出来导热速率是 300 J/s。


……等补充。需计算。


关于这个问题，我一直有个猜测。


有篇文章提到了这个现象的几个事实和几种解释[^2]。


Heat loss due to several ounces of warm fluid leaving the body. Maybe, but then why don't we experience it during defecation, vomiting, etc.?
Heat loss due to exposure of the nether regions. Not likely; as one netter points out, babies snugly clothed in diapers may be observed to experience PMCS.
It's caused by the passage of spermatozoa into the urinary canal. Guess that explains why it happens to women.
It dates back to pre-civilization days when men hadn't learned to do their own shaking. Attributed to George Carlin. What a comedian.
It's all the fault of the parasympathetic nervous system. The parasympathetic nervous system is up there with the Babylonians as the default explanation for anything you can't think of a good reason for (e.g., photic sneeze reflex, closing your eyes when you sneeze), but I throw it in for the sake of completeness. Your mini-orgasm theory sounds like a baroque version of this.


[1]  英文维基 http://en.wikipedia.org/wiki/Urinary_bladder 讲的是300ml - 350ml， 中文维基写的是 300ml - 500ml 。
[2] 文章地址为 http://www.straightdope.com/columns/read/1044/what-causes-piss-shiver
	尿颤用 @赵研™ 的那个解释我一直很怀疑。

	1. 如果尿的温度比其它部分高，那么尿确实是热源。但是即便水的热容很大，可以作为很好的热源，那么我们认为人的膀胱充满尿液的时候体积为 400ml [^1]，那么对应的表面积为 180cm^2 （仅仅对球形的膀胱适用……）。再假定人的膀胱厚度 2mm（充满尿液），与膀胱外组织温差 1℃，导热系数 3000 J/(m s ℃)？？？？？？。这样算出来导热速率是 300 J/s。



	……等补充。需计算。


	关于这个问题，我一直有个猜测。




	有篇文章提到了这个现象的几个事实和几种解释[^2]。



	Heat loss due to several ounces of warm fluid leaving the body. Maybe, but then why don't we experience it during defecation, vomiting, etc.?
	Heat loss due to exposure of the nether regions. Not likely; as one netter points out, babies snugly clothed in diapers may be observed to experience PMCS.
	It's caused by the passage of spermatozoa into the urinary canal. Guess that explains why it happens to women.
	It dates back to pre-civilization days when men hadn't learned to do their own shaking. Attributed to George Carlin. What a comedian.
	It's all the fault of the parasympathetic nervous system. The parasympathetic nervous system is up there with the Babylonians as the default explanation for anything you can't think of a good reason for (e.g., photic sneeze reflex, closing your eyes when you sneeze), but I throw it in for the sake of completeness. Your mini-orgasm theory sounds like a baroque version of this.






	[1] 英文维基 http://en.wikipedia.org/wiki/Urinary_bladder 讲的是300ml - 350ml，中文维基写的是 300ml - 500ml 。
	[2] 文章地址为 http://www.straightdope.com/columns/read/1044/what-causes-piss-shiver