The Pontine micturition center (PMC, also known as Barrington's Nucleus) is a collection of cell bodies located in the rostralpons in the brainstem involved in the supraspinal regulation of micturition (urination). The PMC, when activated, relaxes the urethral sphincter, allowing for urination (micturition). The PMC coordinates with other brain centers, including the medial frontal cortex, insular cortex, hypothalamus and periaqueductal gray (PAG). The PAG in particular acts as a relay station for ascending bladder information from the spinal cord and incoming signals from higher brain areas.
In humans and mammals, neurons in the PMC send descending excitatory projections to spinal parasympatheticpreganglionic neurons innervating the bladder and inhibitory interneurons regulating Onuf's nucleus. Additionally, the PMC receives ascending input from the level of the lumbosacral spinal cord. During bladder filling, neurons within the PMC are turned off. However, at a critical level of bladder distention (when one feels the urge to urinate), the afferent activity arising from mechanoreceptors in the bladder wall switches the PMC on and enhances its activity. This activation results in relaxation of the external urethral sphincter and contraction of the bladder due to stimulation of parasympathetic and inhibition of sympathetic outflow to the bladder, and the removal of somatic activation of the male or female external urethral sphincter. This pattern of activity can also be elicited through the conscious desire to void.