The control of one’s bowels is a pretty basic function. One must be very, very ill to lose it. Are the muscles ‘down there’ especially adapted for control?
Obviously they are voluntary muscles, but are they more controlled than (say) my arm? Could you train a child to keep his arm on his head while he slept? Is bowel control somehow more basic than that?
I note all mammals (I think) exercise bowel control. That would imply something fairly basic is going on.
It’s just like training your kid not to use her pyrokinetic ability.
Actually, it’s a long and drawn-out process. At least ours was.
I’m not sure what the question is. Are you asking why we don’t poop all the time? There are two sphincters at the anus, an internal one and an external one. The internal one is controlled by the autonomous nervous system - you can’t open it intentionally. It’s job is to keep the anus closed, and it’s an involuntary thing. The second, external sphincter is controlled by a spinal nerve, and it’s the one you can “pinch” to sever a bowel movement. cite
If you’re “holding it”, you’re holding the outside sphincter closed while the inside one is relaxing. Sometimes, you can do this for quite a while, and sometimes, not so much.
As for potty training, it’s a matter of teaching the kid to recognize his body’s signals for “internal poop sphincter will be opening in T-minus 4 minutes!” so he can make it to the toilet in time. These sensations come from peristalsis in the gut, as well as a heavy sensation near the anus. Because defecation is more or less uncontrollable (at least until we gain good control of that external closure, but even that’s limited control), and the warning signs are harder to recognize than the urge for urination, it usually takes toddlers longer to control bowel movements than urination.
There’s also an aspect of teaching the kid where it is and isn’t acceptable to urinate or defecate, which certainly isn’t instinctive. It has varied between human cultures at different times. Supposedly in the royal palaces of some European countries in the 1700s, it was OK to pee in the corner of the room.
Forgive me if I was unclear. I was asking if the bowels are under more control by a person than (say) an arm.
Your reply was very informative. So you are saying I do not control my bowels, but rather I react to the signals to get to the bathroom in time? How can that be? If that is the case how do I ‘hold it in?’
You hold it in by clenching the external anal sphincter. Normally when defecation is imminent, feces will enter the rectum and the internal sphincter will relax. If the external one doesn’t relax as well, after a little while the internal one will constrict again and the feces will travel back up into the colon.
If, for some reason, such as an irritated colon or a large volume of feces, the rectum wants to empty really badly, the feces will stay in the rectum and the only thing holding it in will be the external sphincter. Normally this works pretty well, but, as we all know, certain conditions (diarrhea, sphincter fatigue) can cause it to fail, with the expected consequences.