Understanding bowel function
The digestive system includes the mouth, stomach, esophagus, intestines, rectum, and anus. When food or beverages are consumed, they travel through this system until they are eliminated in the form of stool.
Normally, messages are sent from the brain through the spinal cord and sacral nerves. The message tells the body that it is time to empty the bowel.
How the bowel signals fullness
When the bowel is full of stool, it stretches and pushes on the area nerves, which send a sensory message or feeling from the bowel, through the sacral nerves, and then up through the spinal cord. (It is important to eat enough fiber so the stool has enough bulk to stretch the bowel.)
When this sensory message reaches the cord, part of it begins to loop around in the cord setting off a reflex which causes the bowel to squeeze. The other part of the message travels up to the brain. When it reaches the brain, the urge to have a bowel movement is felt.
The decision to empty the bowel
When the person decides it is the right time to have a bowel movement, the message is sent back down the cord, through the sacral nerves all the way to the sphincter muscle near the anus. The message tells the muscle to open up and let the stool out. If it is not a good time to have a bowel movement, the message would then tell the muscle to stay closed until there is a better time to empty.