Eli5: How/ Why does a full bladder wake you up or prevent you from falling asleep?
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Being we just go as infants- I think it is actually learned behavior based on stimulus response. We don’t like waking up covered in urine and needing to deal with the mess, so that feeling of urgency we get from needing to go becomes associated with not staying asleep.
You should never have a full bladder. A full bladder would mean that it could not contain any more liquid and might burst.
Your body has you empty your bladder before it gets full to prevent any problems with your bladder. So your body chooses “an appropriate” time for you to go to the bathroom. When it feels the time is appropriate, it makes you feel like you have to pee and so you pee.
An appropriate time to go to the bathroom is when you are bored or doing nothing in particular. Like when you are resting. That means there is no danger and you can safely go to the bathroom.
So when you wake up in the middle of the night your body decides it would be a good time to pee and makes you feel like you have to pee.
Socialized/learned behavior: peeing in the bed is inappropriate, and–when you’re old enough to have to fix it yourself–a pain in the ass to deal with. The threat, then, of wetting the bed produces an anxiety response
This is layered on top of the physical discomfort of a full bladder. The discomfort tells you that your bladder is full and gets more uncomfortable the more full it gets. You need to consciously relax in order to open your urinary sphincter (can’t remember formal name) or else you would simply just pee yourself constantly all the time. This discomfort serves to tell your conscious mind that the requirement to pee is increasing. It is only as an emergency response that your body will override this requirement of conscious relaxation and force you to pee. This occurs to prevent bladder rupture, but also happens as a fear response. This discomfort system produces enough consistent discomfort to wake you and it happens long before you are forced to pee yourself because the body is easily disrupted from sleep via consistent discomfort.
The reason the body is easily disrupted from sleep via discomfort is predominantly due to the fact that REM sleep is a “shallow” sleep phase much nearer to Level 1 sleep, versus the deep Level 4 sleep that precedes your transition into REM sleep.
Side note: sleep Level 3 and 4 are so deep that stimuli are not readily registered and are the levels of sleep where you are liable to wet the bed. In fact, one women had her scalp chewed on by a fox for approximately 20 bites before she awoke bleeding and in need of immediate medical care. She had a dream where something was pinching her head (dreams happen during the REM phase) before ultimately waking up from the pain.
Overall, the discomfort caused by needing to pee prevents you from sleep in the same way that being hungry prevents you from sleeping: it produces adrenal activation which inhibits fatigue symptoms caused by the build-up of melatonin in your brain throughout the day.
Wow! That’s a really thorough answer. It makes sense now!
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