Central pathways controlling micturition and urinary continence.

The central control of micturition and urinary continence in cats and humans is organized in a similar manner. In cats, 4 areas in the brainstem and diencephalon are implicated in the control of micturition: (1) the pontine micturition center or Barrington area directly excites bladder motoneurons in the sacral cord during micturition; at the same time, it inhibits indirectly, via inhibitory gamma-aminobutyric acidergic and glycinergic interneurons in the medial sacral cord, the external urethral sphincter motoneurons; (2) the pontine continence center activates the external urethral sphincter motoneurons during continence; (3) the midbrain periaqueductal gray receives bladder filling information; and (4) the hypothalamus, in the beginning of micturition. According to positron emission tomography studies, in humans, the same supraspinal regions are active during micturition. Furthermore, the human cingulate and prefrontal cortices are activated during both micturition and continence, indicating that these areas are important for the onset of micturition, but not for the reflex itself. The primary motor cortex of the pelvic floor is important for voluntary pelvic floor contraction, but it is not involved in normal urinary continence.