Computer simulation of the neural control of bladder and urethra

A large number of neural reflex loops may be involved in voiding and leak‐free storage of urine. The simplifying hypothesis that only very few reflexes are needed to account for most of the observed behavior has been tested by quantitative simulation of the lower urinary tract and its control system. The mechanical part of the simulation, involving detrusor contraction strength and a carefully defined urethral resistance, is based on previous work. The postulated neural control system involves two mutually inhibitory control regions, leading to a bistable (storage‐voiding) system, and reflexes driven by a single afferent signal with contributions from bladder wall tension and urethral distension. Because the control system is bistable, each of the two afferent contributions has two possible effects, so that four distinct reflexes appear to operate. Simulations, with and without these reflexes, show that this system accounts for many features of normal voiding, stop tests, and catheter voiding. The behavior is not sensitive to arithmetic details of the calculations involved. After triggering by a simulated suprapontine control signal, the voiding detrusor contraction is initially amplified by the afferent signal from the detrusor but it is sustained until the bladder is empty by the urethral afferent. Mechanical urethral obstruction causes slight residual urine. Breakdown of the mutual inhibition of the two control regions leads to detrusor instability, suggesting that this condition may sometimes have a central origin.