Nervous Control of Micturition

Abstract

The nervous control of micturition has been discussed with special reference to gray substances and fiber tracts in relation to the reflex micturition. The strong, sustained contraction of the bladder with simultaneous relaxation of the external urethral sphincter, characterizing reflex micturition, anticipates not only intactness of certain gray substances in the bulb, pons, and mesencephalon, but also intact-ness of fiber connections between each of these and between these and the spinal vesicomotor centers. Both facilitatory and inhibitory areas related to micturition can be localized in the mesencephalon, pons, and medulla oblongata. At each level, the antagonistic areas are closely adjacent to but distinctly separate from each other. Centripetal pathways subserving this purpose consist of the pelvic sensory vagus in the dorsal funiculus and the sacrobulbar tract in the lateral funiculus of the cord. Participation of the former in mediation of the sensation of passive distentlon as well as of the latter in the sensation of active contraction is experimentally demonstrated. Both spinal pathways terminate in the medulla oblongata. From the terminating nuclei arise the paraalaro-thalamic and juxtasolitario-thalamic tracts. The latter tract especially transmits centripetal impulses related to micturition to suprabulbar centers in the brain stem. There are 3 centrifugal pathways subserving reflex micturition. The lateral reticulo-spinal tract concerned with vesical contraction has 3 sources[long dash]the mesencephalic, pontine, and bulbar. The ventral retlculospinal tract originating from the dorsomedial reticular formation of the bulb subserves relaxation of the bladder. The medial reticulospinal tract contains those fibers originating in the rostral pons (pontine nucleus of the external urethral sphincter); these fibers carry tonic impulses to the external urethral sphincter. In addition to these vesicomotor areas in the brain stem, there are several regions related to micturition in the hypothalamus, the septum pellucldum, the amygdala, and the cerebral cortex. The fiber connections of these areas to the brain-stem centers or to the sacral vesicomotor centers have not been sufficiently elucidated as yet to permit description. There is a bulbar area that, when stimulated, evokes contraction of the diaphragm and the abdominal muscles and relaxation of the perinal muscles. There is a pontlne area that sends tonic impulses to the external urethral sphincter. The roles played by these areas in reflex micturition have been discussed in detail and their possible significance to initiation and interruption of voiding at Till considered.