hi, after seeing “the 40 yr old virgin” (you probably recall the scene… 
) - I was asking myself whats the deal with morning errections?
is there a biological function to fulfill?
thx for sharing your thoughts
al
Having a full bladder can cause erections.
In the morning, men often have a full bladder.
Your morning erection is there to tell you that you can’t get it up with your wife because your marriage is fucked, there is no physical problem.
Well, they make it less likely you’ll wet the bed.
Actually, I’ve read that they happen because the bladder tends to be full by morning, and puts pressure on the prostate, enough to get you a bit aroused in your sleep. And stop you wetting the bed. On the other hand, men definitely normally experience erections on a regular basis during sleep as well; my WAG is that may be just to maintain good blood flow and keep the tissue in good working order.
This question should go into the SDBM FAQs: it’s asked every month or so. And every month people give the wrong answer.
It has nothing do to with urination.
It is caused because, as part of REM sleep, men get erections.
This is so well documented that it’s used as a way to determine if erectile dysfunction is due to a physical cause: if you don’t get erections while sleeping (determined using what’s called “the postage stamp test”*), then it’s a physical problem.
SDMB discussions:
Other References:
http://www.goaskalice.columbia.edu/1518.html
http://www.teenhealthfx.com/answers/Sexuality/879.html
http://www.everything2.com/index.pl?node_id=36446
*You wrap a roll of postage stamps (the old, glued kind) around the penis. If, in the morning, the perferations are intact, you have a physical problem that prevent erections.
so why do those erections persist after you woke up in the morning, then? …
cool!!! … and I aint even married …
so we might have an over-achiever down there …
I am fairly positive that it has something to do with urination. I’ve seen the “no urination connection” floating around in advice columns since the 60’s but never have I ever seen a scientific treatment. I don’t get morning wood without a full bladder. When I do get it, it disappears immediately and unceremoniously when I urinate. I think the origin of this misconception was the 1969 book “Everything You Wanted To Know About Sex *(but were afraid to ask)” which is basically an extended sex-advice column containing both correct and incorrect information.
How would a full bladder even cause an erection? Erections are caused by engorgement with blood. If it was caused by a full bladder, why would this only happen during sleep? We know REM sleep causes erections, and we know the longest periods of REM occur at the end of the sleep cycle. The REM connection just makes more sense.
REM can cause erection - but not every REM period **does **… would be too strange to have erotic content in every REM every day … also it doesnt explain the
“when I pee, the erection goes away” aspects
somebody mentioned a cause-effects path from bladder-prostate-penis
cheers
al
Just a reminder to all Dopers: The cost of first class stamps has gone up 2 cents since last year.
Fighting ignorance and all that…
It’s not a matter of erotic content in your dreams. It’s just a side effect of REM sleep (that crosses gender lines, btw). Your erection dissipates when you pee because most men aren’t physically capable of peeing while erect.
Not to confuse things further, but my “morning wood” happens between 1/2 hour and an hour AFTER I am awake and have gone to the bathroom. Whats the deal with that?
I’m sure there is validity to all the scientific and biological explanations.
Me? I just wake up horny. 
The reason this topic <ahem> keeps popping up, is that there may be more than one answer.
http://www.webmd.com/content/article/14/1685_50264.htm
http://drdrew.com/faq.asp?id=1775
Seems to me that Nocturnal Tumescence can be caused by:
[ol]
[li]Erotic dreams[/li][li]Some mechanism that keeps the blood flowing in the penis[/li][li]A full bladder[/li][li]Being horny[/li][/ol]
I don’t think that there is one answer.
OK, basic logic:
When you have to pee real bad during the day, do you get an erection?
I don’t. It’s more likely to be a hindrance to getting one. So if it was due to having to piss, why don’t you get an erection during the day when you have to go?
It has nothing to do with erotic dreams – it’s a part of regular REM sleep no matter what you are dreaming. You sleep through the other REM erections, so you don’t realize you have had them. It also has nothing to do with the content of your dreams: the very act of dreaming causes the reaction. Google “nocturnal penile tumescence” for the medical name for the condition .
Why it goes away when you pee? Because you can’t urinate and have an erection at the same time. Once you’ve urinated, the erection is gone.
And when sun comes up, the rooster crows, so the rooster is the cause. :rolleyes: Or, in latin, post hoc ergo propter hoc. That’s a logical fallacy.
When you wake up in the morning you usually have full bladder; you don’t always have mornging wood. So whether you get morning wood or not has to be some other factor.
As I said before, any erection disappears immediately when you urinate. In addition, post hoc ergo propter hoc.
No, the actual origin are in texts in both urology and dream research. For instance, the “misconception” is mentioned at WebMD (“Most men have 3 to 5 full erections during deep (rapid eye movement or REM) sleep.”), Journal Articles, College Medical Schools (“About four or five times a night, during the R.E.M. phase of sleep, men usually get some degree of erection.”), Columbia University Health Services (A particularly good link), plus all these links.
Your argument against it, OTOH, is based on a well-known logical fallacy. :rolleyes:
Um… generally, men are physically capable of peeing while erect. What they aren’t capable of is pointing the stream downward easily. But this can be accomplished either by clever sideways maneuvering or by proceeding immediately to the morning shower, where it isn’t a problem if you release the stream directly upward.
In any case, urine definitely is a factor in morning erections for me, and I suspect I’m not the only one. It may not be the sole factor, but it isn’t accurate when people go around saying “it has nothing to do with urination.”
One effect of REM sleep is loss of muscle tone. This is thought to be a mechanism that prevents you from acting out your dreams - you are essentially paralyzed when in REM sleep.
Erections are produced when certain muscles relax and allow blood to flow into the penis. Therefore the muscle relaxation produced by REM sleep is the cause of the erection, not any erotic content of dreams.
Incidentally, females also have clitoral tumesence as a result of REM sleep.
Well, that ain’t the same kind of “morning wood” that the rest of us are talking about, then. I refuse to speculate about the cause. 
How do you know this, exactly? How systematic have your observations of bladder fullness vs frequency of erections been?
You’ve posted links explaining that erections are normal during REM sleep and taken this as evidence that urination cannot be involved, what’s the fancy latin name of that particular fallacy? Are you saying that pressure on the prostate or spinal nerves can’t possibly be involved?