Biology Stack Exchange is a question and answer site for biology researchers, academics, and students. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Just what the title states. It stems from observation & personal experience that a person/dog/cat/monkey is more likely to relieve oneself immediately after it wakes up from the peak-sleep cycle of it's body-clock. Is this observation true? What causes this behaviour ?

share|improve this question
up vote 2 down vote accepted

I think we can actually go farther than mere behavioral argumentation. The separation of the autonomous nervous system into parasympathetic and sympathetic is, one the one hand, associated with the sleep/wake cycle, on the other with parasympathetic/sympathetic activity (low/high epinephrine secretion). This duality certainly applies to all vertebrata (i.e. big animals), as fight & flight is associated with all vertebrata, see e.g.

In other words: from the existence of fight or flight in all vertebrata I infer the existence of a dual autonomous nervous system (parasympathetic and sympathetic) in all vertebrata, although there may be other proof. Since in sleep the parasym. NS is active, the bowel moves. Conclusion: the bowel moves in the sleep of all vertebrata.

share|improve this answer
I'm sorry, I don't understand your answer. Could you elaborate please? – Everyone Sep 30 '12 at 17:37
I have added a reformulation. Better now? – rwst Oct 1 '12 at 6:11

I'm prefixing this one by saying that I don't actually agree with you (also, I think the old nut that the plural of "anecdote" is not "data").

That having been said: wouldn't the simplest explanation just be "because it was likely a long time since the animal's last 'relief'" since it's been sleeping for XXX hours? Or would you argue that this observation is also true after, say, a 20 minute nap?

Also, what does this have to do with a nervous system?

share|improve this answer
Accepted this may be anecdotal; I'll update the question on this & remove the note on the nervous system too. But I would argue the second paragraph with the clarification that an animal/being is more likely to defecate after the typical 'night/rest' cycle which is the 'deepest' such sleep cycle. – Everyone Sep 28 '12 at 19:38

Digestion is an energy consuming process. It is, therefore, often followed by a period of rest. Animals will, consequently, often digest during sleep. It follows that they will eliminate the waste products of digestion upon awakening.

Given the above, I doubt there is a causal link between sleep or rest and the need to commune with nature, water a tree, appease the porcelain god, or whatever your preferred euphemism happens to be, soon after awakening.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.