With a normally functioning bladder, the brain coordinates the filling and emptying.
Messages flow between the spine and the bladder through the automatic nerves, getting the bladder ready to fill. The automatic nerves can work without being connected to the brain. The voluntary nerves only work when connected to the brain.
The bladder is filling and the nerves allow it to fill and stay relaxed. The tap is held tight so nothing leaks out. At this stage the pressure in the bladder is low.
The bladder starts to feel full and tries to empty, using the automatic nerves. The brain becomes aware that it’s time to empty the bladder. The brain can stop the process until a convenient time.
When the time is right, the brain opens the tap and the bladder squeezes the urine out.
Once the bladder is empty the brain closes the tap and the process can start again.
