[Lower urinary tract function and its disorders]

The lower urinary tract provides two modes of operation--storage and elimination of urine. The normal function results in the coordination of contraction and relaxation of muscles of the urinary bladder and urethral sphincters. Disorders of these activities or their interaction lead to the development of lower urinary tract dysfunctions. The nervous system plays an essential role in the regulation of the functions. The control of micturition is coordinated by several regious of the central nervous system. Afferents and efferents of the peripheral nervous system carry signals from and to the lower urinary tract. The reflex circuitry controlling micturition consists of five components: spinal efferent neurons, peripheral efferent neurons, primary afferent neurons, spinal interneurons and neurons in the brain. Preganglionic neurons located in the sacral parasympathetic nucleus and lumbar sympathetic nucleus excite the peripheral efferent neurons innervating smooth muscles of the urinary bladder and urethra. Motoneurons of sacral Onuf's nucleus excite the striated muscle of the external urethral sphincter. Myelinated and unmyelinated afferent axons transmit information from the lower urinary tract to the lumbosacral spinal cord. Three receptor types of the lower urinary tract are present: tension receptors, volume receptors and "silent receptors", which become nociceptors following the sensitization. Afferent pathways terminate on spinal interneurons. Spinal interneurons relay information to the brain or to other regions of the spinal cord. Because micturition reflexes are mediated by disynaptic or polysynaptic pathways, interneuronal mechanisms are of crucial importance in the regulation of lower urinary tract. Central pathways involved in micturition reflexes are located in spinal and supraspinal areas. Micturition reflexes can be modulated at the level of the spinal cord by viscero--bladder and somato--bladder reflexes. Supraspinal areas have a more complicated organization: critical component of the micturition reflex is the pontine micturition center and the periaqueductal gray. Inhibitory and excitatory areas in the pontomedullary and hypothalamic systems and the brain play an important role in the regulation of micturition reflexes.