In your bladder wall, there is a muscle called the detrusor muscle. Normally, the detrusor muscle relaxes to allow your bladder to fill. When your bladder is working as it should, you can control when you go to the toilet. So, when the bladder is full, special nerve sensors detect that your bladder is stretching and that it is time for the detrusor muscle to contract to empty it. Once your bladder is empty, the detrusor muscle stops contracting, and the cycle of filling begins again.