Several muscles and nerves must work together for your bladder to hold urine until you are ready to empty it. Nerve messages go back and forth between the brain and the muscles that control bladder emptying. If these nerves are damaged by illness or injury, the muscles may not be able to tighten or relax at the right time.
In people with neurogenic bladder, the nerves and muscles don't work together very well. As a result, the bladder may not fill or empty correctly. Bladder muscles may be overactive and squeeze more often than normal and before the bladder is full with urine. Sometimes the muscles are too loose and let urine pass before you're ready to go to the bathroom (incontinence).
In other people the bladder muscle may be underactive. It will not squeeze when it is filled with urine and won't empty fully or at all. The sphincter muscles around the urethra also may not work the right way. They may remain tight when you are trying to empty your bladder. Some people experience both overactive and underactive bladder.