Micturition, urinary continence and incontinence

We put forward a novel concept to explain the physiology of micturition. Micturition consists of two stages, first stage in infancy and early childhood and the second stage starts after toilet training. In the first stage, micturition is a sacral spinal reflex. In the second stage, after toilet training, the person builds up, by learning and training, high alpha sympathetic tone at the internal urethral sphincter (IUS) keeping it contracted and the urethra closed and empty all the time. The IUS is a collagen-muscle tissue cylinder that extends from the bladder neck down to the perineal membrane. Its nerve supply is from the thoracic-lumbar alpha sympathetic nerves T10-L2. After toilet training, a gained high alpha sympathetic tone keeps the IUS contracted and the urethra closed and empty all the time.