Dorsal root nerve fibre injury at sacral region of spinal cord can cause:

Atonic bladder: Caused by destruction of sensory nerve fibers, thereby preventing transmission of stretch signals from the bladder. Instead of emptying periodically, the bladder fills to capacity and overflows a few drops at a time through the urethra. This occurrence is called overflow incontinence. A common cause of atonic bladder is crush injury to the sacral region of the spinal cord. Automatic bladder: Caused by spinal cord damage above the sacral region, with intact sacral cord segment Micturition reflexes are no longer controlled by the brain Periodic (but unannounced) bladder emptying occurs Neurogenic bladder: paial damage in the spinal cord or the brain stem interrupts most of the inhibitory signals. Facilitative impulses passing continually down the cord keep the sacral centres so excitable that even a small quantity of urine elicits an uncontrollable micturition reflex, thereby promoting frequent urination.