Normal and abnormal voiding

The left panel illustrates the mechanics of normal voiding. The detrusor musculature contracts to empty the bladder, while the external sphincter relaxes to open the bladder neck and release urine. The right panel illustrates the voiding dysfunction seen in patients with a high-pressure or hyperreflexic bladder. The detrusor muscle is over active, which interferes with bladder filling. Some patients also have poor relaxation of the external sphincter during voiding or poor coordination between the bladder and sphincter (detrusor-sphincter dyssynergia), causing high bladder pressures and inefficient emptying.