IQl8 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



FIG. 17. Dorsal view of the lower brain stem of dog with 

 cerebellum removed. The location of points producing contrac- 

 tion shown by dots on the left. Points more laterally and deeply 

 located, which relaxed the bladder are shown by triangles on 

 right. Barbiturate anesthesia and Marey tambour recording. 

 [From Kuru & Hukaya (17).] 



is a micturition facilitatory area in its own right or a 

 way station from the cerebral cortex is not clear. Its 

 influence on the bladder is exerted through the 

 sacral nerve roots whereas unsustained contractions 

 may employ sympathetic efFerents and may be 

 trigonal in origin. 



Since ablation experiments indicate that the blad- 

 der, unlike many other viscera, is not represented at 

 the medullary level, interest attaches to the observa- 

 tions of Kuru & Hukaya (17), embodied in figure 17, 

 who found vesicle excitatory points in the medulla. 

 Kuru (16) also traced afferent pathways from the 

 sacral segment to this same region {vide infra), sug- 

 gesting an additional brain-stem level concerned 

 with bladder activity, although presumal)ly not 



exerting tonic control since subcollicular and spinal 

 transections are equivalent. However, whether fibers 

 of passage or a 'center' was stimulated is not deter- 

 mined. 



The two summary diagrams (fig. 18) convey the 

 complexity of descending influences on the mic- 

 turition reflex. It is a considerably more extensive 

 apparatus than that envisaged by clinical neurolo- 

 gists and urologists. Bladder control is clearly repre- 

 sented at successive levels of the neural axis, just as is 

 the control of somatic reflex activities. It seems un- 

 likely that in man this whole apparatus except its 

 cortical and spinal termini could have fallen into 

 desuetude. 



Pathological Physiology of Human Micturition 



Only those abnormalities which are neurogenic 

 need be discussed. There are substantial differences 

 in terminology (cf. 20, 23, 25), and terms have been 

 chosen which have unfortunate connotations in re- 

 spect to neural mechanisms.* 



U.MNHIBITED NEUROGENIC: BL.^DDER (McLeLL.^iN). 



Caused by damage to cerebral structures or subtotal 

 interruption of spinal pathways, according to 

 McLellan (20), this condition is characterized by 

 urgency, small-volume thresholds and frequent 

 micturitions that empty the bladder. Continence is 

 usually maintained, perhaps by the external 

 sphincter. Cystometricalh', the abortive micturition 

 contractions, accompanied by a desire to micturate, 

 may occur at an initial 25-ml increment and at each 

 subsequent increment; or contractions may not occur 

 until a normal bladder \olume is reached but are 

 then imperative. The tonus curve may be within the 

 normal range, or somewhat steep, a change we 

 ascribe to smaller than normal micturition volumes. 

 This situation is similar to that produced experi- 

 mentally in cats by intercollicular and transhypo- 

 thalamic transections. Howe\er, the laboratory and 

 clinical workers differ in their interpretation. Clinical 

 accounts emphasize a) release of a spinal reflex from 

 cortical inhibition, and b) by implication, the cortico- 

 spinal tract is the inhibitory agent. Neurophysiologi- 

 cal experiments suggest that the low threshold and 

 the strength of the detrusor contraction are due, not 

 to the spinal reflex arc's acting alone, but to its 



* Expressions like 'neurogenic bladder' and 'cord bladder' 

 are clinical jargon, and substitutes should be found. This is 

 apparent if one reflects for a moment on the literal meaning of 

 the phrases. 



